#hydronicheating

Waking up to a cold house because your boiler shut down overnight or worse, finding your system overheated and damaged from runaway temperatures is every homeowner's nightmare. Understanding what an aquastat is and how it controls water temperature in your heating system means you'll avoid these problems while keeping your home comfortable and your equipment running safely for decades.

The Simple Truth About What Aquastats Actually Do

An aquastat is basically a thermostat for water instead of air. While your wall thermostat watches the room temperature, an aquastat monitors the water temperature inside the boiler and adds water when needed. It informs the burner when to fire, and when to shut off, as a function of how hot the water is. (Otherwise you wouldn’t have any automatic control over the boiler temperature.)

You can think of it as the brains behind your hydronic heating system ensuring that the temperature remains within a safe, efficient range at all times. Too hot and you could end up boiling the water, creating dangerous pressure or breaking devices. Too cold and you’re wasting fuel heating water that’s too cool, or not enough heat when it is needed. The aquastat maintains this balance for you.

How the Temperature Sensing Mechanism Works

Inside the aquastat, there's a sensing bulb filled with liquid or gas that expands when heated and contracts when cooled. This produces a mechanical force that in turn closes or opens an electrical circuit. Modern electronic versions have replaced the mechanical expansion with thermistors that send electrical signals instead, but the idea is the same.

The bulb is normally places in protective metal sleeve which takes the name of a well or thermowell and directly into boiler water. As the water heats up, the stuff inside of the bulb expands and grows until it flicks the switch off and kills power to that burner. When water cools, contraction resets the switch so that the burner can fire anew.

Understanding Differential Settings That Prevent Short Cycling

Differential is the temperature range below your high limit setpoint where the aquastat allows the burner to restart. If your high limit is 180°F and your differential is 15 degrees, the burner won't fire again until water drops to 165°F. This prevents short cycling where the boiler turns on and off constantly, which wastes fuel and hammers components with excessive starts.

Too tight a differential causes rapid cycling that kills efficiency and shortens equipment life. Too wide and you get big temperature swings that affect comfort and system performance. Most residential systems work well with 10 to 20 degree differentials depending on boiler size and heat loss. We usually start around 15 degrees and adjust based on how the system actually operates.

High Limit Protection Keeps Your System Safe

The high limit function is your primary safety control.It turns the burner off when water reaches its maximum temperature, which is usually around 180-200°F depending on how your system was designed. This also prevents components from getting boiled, preventing things that can crunch in extreme temps.. Every hydronic system needs reliable high limit protection.

When a high limit trips, figure out why before just resetting it. Overheating can be the result of anything from low water, circulator pumps failure, closed valves or excessive scale. The aquastat is supposed to shut off. Instead of bypassing or ignoring the safety control that just saved you from costly damage or worse, fix the real problem.

Low Limit Maintains Minimum Temperature for Efficiency

Low limit settings keep a minimum water temperature in the boiler even when no heat is being called for. This is common in systems providing domestic hot water where you want the boiler ready to deliver hot water instantly. Settings around 140 to 160°F keep enough heat available without constantly firing the burner from cold.

The tradeoff is standby heat loss from maintaining this minimum temperature versus savings from not reheating the entire boiler mass every time you need hot water. For systems with frequent domestic hot water use, low limit makes sense. For heating only systems in mild climates, you might not bother maintaining minimum temperature during shoulder seasons.

Circulator Control Timing Matters for Efficiency

Circulator control aquastats manage when pumps move water through the system. You don't want pumps running when water isn't hot enough to provide useful heat. The aquastat holds the circulator off until water reaches adequate temperature, then allows it to run. This prevents cold water circulation that would cool down radiators or radiant floors instead of heating them.

Pairing aquastat control with quality circulators like the Grundfos Circulation Pump Kit gives you precise control over heat delivery. The pump only runs when conditions are right, saving electricity and preventing the comfort issues that come from circulating water that's not hot enough to heat properly.

Triple Aquastats Simplify Complex Control Needs

Triple aquastats combine high limit, low limit, and circulator control in one device. This cleans up wiring, simplifies troubleshooting, and often costs less than buying three separate controls. For systems needing all three functions, the integrated approach makes installation and service much easier. One device to mount, one set of wires to connect, one unit to replace if problems develop.

The downside is if one function fails, you're replacing the entire unit instead of just the failed component. For most residential applications this isn't a big deal since the units are reasonably priced and failures are rare when properly installed. Commercial or critical applications might prefer separate controls for redundancy.

Mounting Methods and Accuracy Considerations

Immersion Installation Sensing bulb goes directly into water through a protective well, provides most accurate temperature reading and fastest response.

Strap-On Installation Device clamps to exterior of supply pipe, easier to install but slightly less accurate than immersion, works fine for less critical applications.

Remote Sensing Bulb connects to controller via long capillary tube, allows mounting controller away from heat source, useful when space is tight near boiler.

Electronic Sensors Use thermistors instead of mechanical expansion, faster response and better accuracy, easier integration with modern control systems.

Common Problems and What They Mean

Aquastats that trip constantly usually indicate boiler overheating from low water, failed pumps, or restricted flow. Aquastats that never satisfy might have failed sensing bulbs or incorrect settings for the system. Erratic behavior often points to failing bulbs giving inaccurate readings or loose electrical connections causing intermittent operation.

If your differential setting seems wrong for the cycling pattern you're seeing, the aquastat might be reading temperatures incorrectly due to scale on the well or a partially failed sensor. Clean the well, verify settings, and test operation before assuming the control is fine. Many aquastat replacements happen when the real problem is elsewhere in the system.

Maintenance and Testing Procedures

Check aquastat settings at the start of each heating season to verify they haven't drifted. Mechanical units can shift over time and use. Test high limit operation annually by monitoring boiler temperature rise and confirming shutoff happens at the set point. This is critical safety verification that takes five minutes.

Clean sensor wells when you do annual boiler service. Scale and sediment insulate the bulb from actual water temperature, causing inaccurate readings and poor control. Pull the well, clean deposits, reinstall properly, and verify the sensor is making good contact. While you're in there, check electrical connections for corrosion or looseness.

Choosing the Right Aquastat for Your System

Match the control to your application. Heating only systems might need just high limit and circulator control. Combination systems providing domestic hot water benefit from triple aquastats with low limit capability. Large commercial installations might need separate controls for redundancy and zoning flexibility.

Consider electronic versus mechanical controls based on your situation. Electronic units offer better accuracy and integration with modern heating controls. Mechanical units are simpler, often cheaper, and don't require external power beyond the control circuit. Both work fine when properly selected and installed for the application.

Frequently Asked Questions

What temperature should my aquastat be set at? High limit around 180°F and differential of 15 degrees works for most residential hydronic systems.

Can I adjust my aquastat settings myself? Yes, but understand your system's requirements and never disable or bypass high limit safety controls.

How long do aquastats typically last? Ten to fifteen years with proper maintenance, though mechanical parts can fail sooner under harsh conditions.

What causes an aquastat to fail? Age, corrosion, scale buildup on sensors, or electrical problems from moisture or poor connections.

Do all boilers need aquastats? Every hydronic heating system needs temperature control, though specific configurations vary by application.

Getting Temperature Control Right

Aquastats are the essential controls that keep hydronic heating systems operating safely and efficiently. They protect against overheating damage, regulate the on/off cycling of burners, direct circulation operation and offer low water temperatures for both comfort and super longevity. Knowing how they work can help you maintain them properly and identify problems before they’re costly failures.

Watching heat pour out your chimney while your water heater and furnace run on expensive electricity feels like burning money along with your firewood. This guide walks you through installing heat exchangers for wood burning stoves that capture otherwise wasted heat for forced‑air distribution, domestic water heating, and supplemental room warming.

Understanding your heat exchanger installation options

Three main installation types serve different heating needs:

Water‑to‑air exchangers integrate with your existing forced‑air furnace to distribute wood heat through the ductwork.

Flue or chimney‑mounted exchangers capture heat from exhaust gases before they escape up the stack.

Water‑to‑water exchangers preheat domestic hot water before it enters your conventional water heater, reducing its energy consumption.

The best type for you depends on your existing home heating system and your goals. Forced‑air applications, in homes that have forced‑air systems, will often find a plenum‑mounted water‑to‑air unit a beneficial choice — using existing ducts to circulate warmed air. Freestanding wood stoves are often matched with flue‑mounted exchangers that heat the air in the room without a pump, or long lengths of pipe. Preheating of domestic water is justifiable when hot‑water consumption and wood‑burning hours warrant the extra sophistication.

Installing water‑to‑air exchangers in furnace plenums

Mount the water‑to‑air heat exchanger in the hot‑air supply plenum so it can warm all the air your furnace distributes. If you already have an air‑conditioning coil: Many installers and manufacturers suggest situating the hot‑water coil upstream of the AC coil, with a few inches between them (e.g. about 4”) for serviceability and so as to not freeze / not condense return air too much. Consider that spacing standard procedure, not code for a one‑size‑fits everything; always adhere to your equipment manuals and local codes.

You can also cut the plenum to size and support it with angle iron, or use an “H‑cut” technique on the front and back panels and pass the exchanger through. All edges and openings in the opening must be sealed with HVRAC‑rated foil tape or high temperature sealant to prevent air bypass around fins (Air bypass will reduce heat transfer). Connecting supply to the bottom of the coil and return to the top is a technique often used to help vent air and ensure good flow.

Learn How to Size Unit Heaters for Garages

Flue‑mounted exchangers for direct heat recovery

Chimney or flue heat exchangers replace a section of stovepipe above the stove collar and capture heat from flue gases. They can work by passive radiation or with a blower that moves room air across hot tubes or plates.

However, cooling flue gases too much has trade‑offs. Cooler flue‑gas temperatures lead to increased creosote buildup and draft weakness. When an oversize or improperly-installed flue reclaimer is operated on seriously-cooled exhaust, it can hurt combustion efficiency and even create smoke spill-back, carbon monoxide problems. Expect to have your chimney more frequently inspected and cleaned than if you had an unmodified flue, and never install something that becomes a major obstruction of the flue or that reduces draft below what your stove and chimney were designed for.

Domestic water‑heating installations

Water‑to‑water heat exchangers for domestic hot water should be piped with a proper bypass arrangement so you can isolate or bypass the exchanger for summer or service. You have options with the three‑valve bypass (inlet, outlet and straight‑through bypass). Running the exchanger in counterflow (boiler water & domestic cold entering from opposite ends) maximizes heat transfer.

Thermosiphon systems don't require pumps as water will naturally rise into a storage tank if the tank is placed above the heat source with supply/return connections. To create dependable thermosiphon, you need to use larger‑diameter lines (typically 3/4-inch and 1 inch instead of 1/2 inch) so as to minimize flow resistance, and keep the runs as short and smooth as is practical. Any domestic‑water heating off a wood system must also follow local plumbing code, including:

Approved materials and backflow protection

Scald protection using mixing/tempering valves on outlets, since wood systems can produce very high water temperatures

Proper pressure‑relief and expansion‑control devices

Powered systems using a wood boiler pump offer more freedom in tank location and more consistent circulation but still must meet the same safety and code requirements.

Critical safety considerations

Never sacrifice chimney draft for extra heat recovery. Following installation of any flue related equipment verify per their test procedure draft on external devices and smoke spillage into the room is absent. Fit carbon monoxide detectors and check them frequently.

Any water tightly closed or of the closed pressure system, which is connected to a wood appliance needs proper-sized temperature‑and‑pressure relief valves and expansion control. Relief discharge must be routed where it cannot scald people or damage property. Test or replace relief valves according to manufacturer recommendations.

Review EPA Standards for Wood Burning Safety

Remember that EPA residential wood‑heater standards are emissions rules for new stoves, furnaces, and boilers—governing how the appliances are tested and certified. They do not directly regulate your underground piping, ductwork, or add‑on heat exchangers, though good distribution design still matters a lot for your efficiency and fuel use.

Plumbing connections that last

Use copper or steel on the hottest boiler‑side piping near the stove or boiler, and only use PEX where temperatures are within its rating and it is protected from hot surfaces. Support all piping to avoid sagging and stress at connections. IProvide serviceable shut off valves on supply and return of each Exchanger. Install dielectric unions at the juncture of dissimilar metals to inhibit galvanic corrosion, especially with aggressive water.

Sealing, insulation, and commissioning

Seal around water‑to‑air coils so all air is forced through the fins. Use HVAC foil tape and high‑temp sealants in place of standard duct tape. Insulate the hot‑water lines from stove/boiler to exchanger to reduce standby losses; even on short runs without insulation, significant heat can be lost.

On system start up, fill and vent water circuits slowly, expel air from high points and pressurize to normal operating pressure. Check every joint for leaks before running at full temperature. Begin with small fires while you verify that temperatures, flows, and air distribution behave as expected, then fine‑tune pump speeds and valve positions.

Maintenance and performance

Clean dust and lint from water‑to‑air exchanger fins at least annually.

Inspect water‑side connections for scale, corrosion, and leaks.

Clean flue‑mounted exchangers and chimneys more often than you would with a bare flue, since cooler gases accelerate creosote buildup.

Watch for any signs of poor draft, smoke rollout, or CO alarm activity and address immediately.

Your heat‑exchanger installation questions answered

Can you install heat exchangers on any wood stove? Most stoves can work with external exchangers, but mounting options and safe configurations depend on the stove and chimney design.

Do heat exchangers always improve efficiency? They can significantly improve how you use the heat you produce, but overly aggressive flue cooling can hurt combustion if not designed correctly.

How much can they save? Savings vary widely by climate, system design, and wood usage; some setups see large reductions in backup fuel use, others more modest gains.

Do they need electricity? Thermosiphon water systems can be passive, but most water‑to‑air units rely on blowers and/or pumps for effective distribution.

Your outdoor wood boiler can heat your entire house for pennies on the dollar, but only if the water keeps moving. A pump that's too small starves your system, while one that's oversized just burns electricity without giving you better heat. We'll show you exactly how to choose and install an outdoor wood boiler pump that matches your loop length, handles the head pressure, and keeps circulating for years without breaking down.

Calculate Your Pump Size Based on Distance and Resistance

The biggest mistake people make is guessing pump size without measuring their actual loop. Measure the total distance from your outdoor boiler to the house and back, then add up every bottleneck in the system. Heat exchangers, filters, and zone valves all create resistance that your pump has to overcome.

For loops under 50 feet with just one heat exchanger, a Taco 007 handles the job fine.For the typical average house, 75 to 125 feet in length, that means a Taco 009 or Grundfos 15-58 would be required. If you’re pushing over 150′, or have multiple exchangers (forced air PLUS dhw), move up to a Taco 0011, or wood boiler rated 2400-20 pump. These bigger units move 8 to 10 gallons per minute even when fighting serious head pressure.

Pick a Bronze Cartridge Pump Built for Wood Boiler Conditions

Standard cast iron pumps work fine for closed heating loops, but outdoor wood boilers run open systems that eat through basic components fast. Bronze cartridge models like the Taco BF5-J series last longer because they resist corrosion from well water and outdoor conditions. We've seen bronze pumps run 5 years or more in setups where cast iron barely made it through two seasons.

Here's what works for different situations:

Taco 007-BF5-J: Short loops under 50 feet, simple single-exchanger setups, carries a 3-year warranty (1-year for wood use).

Taco 009-BF5-J: The workhorse for most homes, handles 30 to 125 feet with solid efficiency and flow.

Taco 0011-BF4-J: Larger properties running 100 to 200 feet, moves enough water for multiple zones.

2400-20 Wood Boiler Pump: Purpose-built for long runs up to 400 feet, carries a full 3-year wood-specific warranty.

Armstrong E-series pumps are also a good choice, if you want high-efficiency motors that consume less electricity, but still provide the same flow.

Install the Pump on the Supply Line Near the Boiler

Mount your pump on the hot supply line right where it exits the outdoor boiler, before it hits any heat exchangers or splits into zones. This maintains the pump primed all the time and no air is collected in impeller. Always mount the motor shaft horizontally so that air will not pool in the bearings and result in premature failure.

1 to 1.25 inch PEX(This had the oxygen barrier) all the way around. Putting isolation ball valves on each side of the pump will allow you to swap out that pump later on, without having to drain 200 gallons from the system. Wire it to its own 120V circuit with a GFCI outlet, and orient the flow arrow on your pump body away from the boiler (towards the house). Accessory to your pump is a boiler aquastat that provides only circulation at water temperatures above 140-160F for instance.

Check EPA wood heater standards for safe installation: EPA Residential Wood Heaters

Test Flow Rates and Troubleshoot Common Pump Problems

Before you backfill any trenches or close up walls, prime the pump and check your flow rate. You want 8 to 10 GPM moving through the system, which equates to a water velocity of around 4-10 feet per second in 1-inch PEX. Listen for cavitation noise (gravelly sound in the pump), which means you’ve either got air your lines or your pump is running dry.

The majority of pump failures result from dead bearings nobody had greased, clogged strainers that choke the flow and air locks never purged. * Rinse and flush your inline strainer every three months while heating, and check the pump once a year for leaks around the seals. If you hear grinding or the motor starts running hot, shut it off and inspect for obstructions. Watch the difference in temperature across your heat exchanger – there should be ~20°F drop when all is well.

FAQ Section

What size pump do I need for a 100-foot outdoor wood boiler loop? A Taco 009 or Grundfos 15-58 handles most 100-foot loops with one or two heat exchangers.

Should I install the pump on the supply or return line? Always install on the hot supply line near the boiler to keep the pump primed and prevent air pockets.

How often should I maintain my outdoor wood boiler pump? Flush the inline strainer quarterly and inspect the pump annually for leaks and bearing wear.

Can I use a standard circulator pump for an outdoor wood boiler? Standard pumps work but bronze cartridge models last longer in open wood boiler systems with well water.

What GPM flow rate should my outdoor wood boiler pump deliver? Target 8 to 10 GPM for most residential systems to ensure efficient heat transfer and prevent overheating.

Keep Your Heat Moving All Season Long

Selecting and setting up the right pump makes the difference between a wood boiler that heats efficiently and one that wastes fuel while you freeze. Right pump size for your total loop length and head pressure (and go bronze). And get the pump on the supply line and pipe in isolation valves. Test your flow rates, bleed the air, and keep up with strainer maintenance for years of smooth operation.

There's nothing quite like jumping into a warm pool on a cool evening or walking into a perfectly heated home in January, knowing you're burning wood you cut yourself instead of paying through the nose for propane. Getting there starts with sizing your wood boiler heat exchanger correctly, because an undersized unit leaves you shivering while an oversized one wastes fuel and money. Here's how to match your exchanger to your actual needs, whether you're heating thousands of gallons of pool water or keeping your family comfortable all winter.

Sizing Your Wood Boiler Heat Exchanger for Swimming Pools

The standard target for pool heating is raising water temperature by 1 to 2 degrees per hour. That’s fast enough to let you have a pool without having your wood boiler going 24 hours a day. A 100,000 BTU heater will raise a 15,000 gallon pool about one degree/hour under average conditions. Scale up or down from that number, depending on your pool size.

Simple math for planning purposes, say 4 BTUs per gallon to hold a temp in summer or 6 BTUs when working against the cooler ambient outside temps of fall and spring. A 6,000 gallon pool will require a capacity of approximately 85,000 BTUs. A larger pool of 15,000 to 25,000 gallons? You’re in the vicinity of 370,000 BTU. In a 27,000-gallon setup you’re going to be in the neighborhood of 360,000 BTU. Material matters too. Get 316L stainless steel if you have a chlorine pool and get titanium if you have a salt water pool in order to prevent the corrosion that will eat your exchanger up from the inside. OutdoorBoiler.com stocks both types built specifically for outdoor wood boiler applications where durability actually counts.

Ready to heat your pool the smart way? Check EPA-certified wood boiler standards at the EPA Standards page for efficient, compliant heating.

Sizing Your Wood Boiler Heat Exchanger for Home Heating

Home heating is a different animal because you're sizing brazed plate heat exchangers based on square footage, climate, and how much BTU load your space actually needs. Start with your climate zone. Cold climates require 30 to 50 BTUs per square foot for a standard room with 8 foot ceilings. The moderate zones can scrape by on 20 to 35 BTUs per square foot.” Mild ones where you need to warm things for only part of the year? So you can get down to 10 to 20 BTUs per square foot.

Plate count closely follows square footage. A home that is less than 2,500 sq ft runs great with a 30 plate exchanger. Step up to 40 plates, anywhere from 2,500 to 4,000 square feet. Anything up to 4,000 or even 6,000 square feet needs a 50 plate unit. When you get to 50 plates or more, ensure the connections are a minimum of one and a quarter inch MPT. Smaller connections create pressure drops that kill efficiency. These calculations work hand in glove with proper system design, similar to sizing a unit heater for a garage where matching capacity to space is everything.

The BTU Formula for Precision Sizing

When rules of thumb aren't cutting it or you've got a custom setup, run the actual numbers. The formula is BTU equals GPM times 500 times delta T. GPM is your flow rate in gallons per minute. Delta T, is the difference in temperature of the water going into and coming out of the exchanger. Easy example: 20 GPM flowing at a 20 degree temperature drop equals 200,000 BTU capacity.

This equation allows you to cross-check against manufacturer specs or fine-tune the specific load if you're working with an odd configuration or multiple zones. Online calculators can hasten it all along, but if you know the math, you can also troubleshoot on the fly. That piece of the puzzle is the same whether we are talking about heating a pool, a house or a shop building. Flow rate and temperature differential determine capacity, period.

Material Choices and Mistakes to Dodge

Stainless steel and titanium are your friends for pool applications where corrosion from chemicals or salt is a constant threat. For home heating with brazed plate exchangers, copper brazed stainless handles standard hydronic systems beautifully. The most common sizing mistakes? Ignoring your actual climate zone and just guessing, or using connection sizes too small for your plate count. Both kill performance.

Pairing the right exchanger with properly insulated PEX distribution lines completes the efficiency picture. You can have the perfect exchanger, but if heat is bleeding off through bare pipes on the way to where you need it, you're still wasting wood. OutdoorBoiler.com carries the full range of exchangers, from compact 30 plate units for smaller homes to heavy duty pool heaters that'll run for decades. They stock the stuff that holds up because they know what fails in the field.

Get Your Wood Boiler Heat Exchanger Sized Right the First Time

Sizing comes down to knowing your pool volume or home square footage, matching that to BTU requirements for your climate, and picking materials that won't corrode out in three years. Use 4 to 6 BTUs per gallon for pools and 10 to 50 BTUs per square foot for homes depending on where you live. When precision matters, run the GPM times 500 times delta T formula. Get it right and you'll have faster heating, better fuel economy, and a system that lasts.

Stop guessing and start heating efficiently. Head to OutdoorBoiler.com for wood boiler heat exchangers sized for real installations, plus all the outdoor wood boilers, furnaces, and accessories you need to build a system that actually works. Their technical support knows the difference between catalog specs and what performs in January.

FAQs

How many BTUs do I need per gallon for pool heating? Use 4 BTUs per gallon in summer and 6 BTUs per gallon in spring or fall.

What size heat exchanger do I need for a 3,000 square foot home? A 40 plate brazed exchanger works for most moderate climates at that size.

Can I use stainless steel for a saltwater pool? No, saltwater pools require titanium heat exchangers to prevent rapid corrosion.

How do I calculate exact BTU capacity? Use the formula BTU equals GPM times 500 times the temperature differential.

There is nothing worse than watching your heating dollars disappear into frozen ground because someone cut corners on the heat main. Homeowners who “wing” underground boiler piping often end up with high fuel bills and mid‑winter repairs. Here is what you need to know about laying underground boiler pipe correctly, from planning your route to final backfill.

Planning your underground boiler pipe route

The shortest practical route usually saves money by reducing pipe length and heat loss. Walk your property and find the most direct route from your outdoor boiler to where pipes will enter your home, avoiding areas you might pave or build later, major tree roots, septic systems and wells.

Before you dig, be sure to call 811 or your local utility-marking service. The material charge is miniscule, in many jurisdictions it's free, and much safer than taking a chance on hitting a gas or power line. Measure the intended route and add additional length for depth changes, slight bends, and some clean connection work at each end. Make a drawing of the path and depths so you have a record for future troubleshooting or expansions.

Digging the trench

For many residential outdoor‑boiler installations, trenches are often dug roughly 18–24 inches deep when not under traffic, but this is only a starting point. The correct minimum depth is what your local code and frost depth is; in colder climates that can be much deeper than 2 feet. Deeper burial (frequently around four feet) and extra protection under driveways or vehicle paths, is typical.

A trench width of about 6 inches is usually sufficient for a two‑pipe insulated bundle. And if you’re going to add electrical in the same trench, remember that the depth of burial and type of cable (among other things) need to meet electrical code requirements and local codes — not some random 6-inch separation.

Bedding and laying the pipe

Place a few inches of clean sand or fine, rock‑free fill in the bottom of the trench before setting the pipe. This prevents damage to the insulation jacket and ground settling. Once the pipe is in position, add an additional layer of sand or clean fill over it before re-covering with native soil.

Unroll pre‑insulated PEX carefully to avoid kinks. Leave the end caps on or wrap in tape until you can connect to avoid dirt and water getting into your lines. Where the pipe enters a building, drill or core into it at a slight upward angle, sleeve as necessary and seal around with waterproofing materials to help keep groundwater out of the structure.

PEX‑a and PEX‑b are popular for use in underground applications, as they can bend around obstructions without the need for a fitting at each turn. For hydronic applications, PEX with an oxygen‑diffusion barrier is critical in closed, pressurized systems that may cause oxygen to enter and corrode the boilers, radiators and cast‑iron pumps. For open, non‑pressurized outdoor wood‑boiler systems, barrier pipe is generally not necessary to control corrosion in the boiler water and supply piping (I refuse to even use oxygen-barrier PEX for these systems) but many installers also like the idea of using oxygen‑barrier PEX for the closed parts of a system and any outlets which may be needed in locations that cause accessibility or service issues.

Making reliable connections

Use manufacturer‑approved crimp, clamp, or expansion fittings and the proper tools. There are also fittings and pipe that must be rated for the boiler pressure and temperature (which is sometimes much higher than standard plumbing). Every underground connection is a possible leak, so keep the number of fittings in buried pipe to an absolute minimum.

Pressure‑test the piping before any backfill. Pressurize to at least normal operating pressure (often somewhat higher per manufacturer guidance) and watch the gauge for a set period. Any pressure drop indicates a leak that must be fixed while everything is still exposed.

Backfill in layers, starting with sand fill of fine material above the pipe followed by compacted native material in small loose lifts. To avoid crushing the jacket, do not tamp over the insulated line (especially where rocks or other hard objects are present).

Why pre‑insulated PEX with barrier is preferred

Pre‑insulated PEX (with or without oxygen barrier, depending on system type) is the standard for outdoor boiler supply and return lines. Proper insulation keeps heat in the water rather than warming the soil, and quality outer jackets protect the system from moisture and physical damage. PEX is also more tolerant of freeze events and soil movement than rigid materials.

By contrast, bare copper lines underground lose far more heat and are susceptible to corrosion if not perfectly protected, and standard PVC is not rated for the high temperatures typical of outdoor boiler systems. While the EPA’s residential wood‑heater rules focus on emissions performance of the boiler itself, not distribution piping, good underground piping still plays a major role in your real‑world efficiency and fuel use: the less heat you lose between boiler and building, the less wood you burn for the same comfort.

Your next steps

Getting underground boiler pipe installation right comes down to careful planning, appropriate materials, following local codes and frost‑depth requirements, and taking time to test before backfilling. Plan your route, dig to a code‑compliant depth, protect the pipe with proper bedding, pressure‑test all connections, and use insulated PEX that is correctly rated for your system and type (closed or open).

Hey everyone,

Been doin' some research on heat exchangers lately, and figured I'd share what I've learned about the water-to-water plate heat exchangers from Outdoor Boiler. Might be helpful if you're thinkin' about gettin' one.

What it Does:

Basically, a plate heat exchanger lets you transfer heat from one water source to another without them mixing. This is super useful in a few situations with outdoor boilers:

Hot Water: You can use it to pre-heat the water goin' into your regular hot water heater. Keeps your domestic water clean and separate from the boiler water (which has anti-corrosion stuff in it).

Indoor Heating (Baseboard/Radiant): If you're heatin' your house with an indoor boiler and baseboard heat, this can help boost the temp of the water comin' back from the house loops. It also keeps the outdoor boiler water separate from the indoor boiler system, which is important 'cause indoor systems are pressurized and outdoor ones aren't. Plus, outdoor boilers can have sediment that you don't want cloggin' up your indoor system.

In-Floor Heating: Similar to the above, but extra important for in-floor heat. In-floor systems often have antifreeze, and they need to run at much lower temps than your outdoor boiler. The plate heat exchanger keeps everything separate and lets you run each system at the right temperature.

Key Things to Know (Based on Outdoor Boiler's Site):

Sizes: They got different sizes (20 plate, 30 plate, 40 plate, 50 plate, 60 plate, 80 plate, 100 plate) depending on how much heat you need to transfer (BTU transfer).

Connections: Most have 1" connections, but the bigger ones (60 plate and up) have 1-1/4" connections.

Stainless Steel: Made with 316 stainless steel plates, which is good for long life.

Import Alert: They mention that some imports are smaller and use lower-grade stainless steel, so make sure you compare carefully.

Why You Might Want One:

If you're lookin' to use your outdoor boiler for more than just one thing (like heatin' your house and your hot water), or if you need to keep different water systems separate for safety or efficiency reasons, a plate heat exchanger is the way to go.

Check it out here:https://outdoorboiler.com/collections/heat-exchangers/products/outdoor-boiler-water-to-water-plate-heat-exchanger

Nothing ruins a cold winter evening faster than discovering half your house is warm while the other half stays freezing because your pump can't push water through your heating zones properly. This guide shows you how to select circulating pumps that actually match your system's needs, delivering consistent heat throughout your home without wasting electricity or creating noise issues.

Why Pump Selection Actually Matters

An undersized circulating pump struggles to move enough water through your heating system, leaving distant rooms cold while zones near the boiler stay toasty. Oversized pumps waste electricity running at higher speeds than necessary and create water hammer noise that echoes through your pipes every time they cycle on. Getting the match right means balanced heat distribution, lower operating costs, and quiet reliable operation that you never have to think about.

Modern variable speed pumps with ECM technology can reduce energy consumption by up to 80 percent compared to old fixed speed models that run full blast regardless of actual demand. That efficiency converts to annual electricity savings of $100 to $200 for typical residential systems, and that in turn pays back the modest price premium on quality pumps in only a couple of years. The correct pump also helps to protect other parts of the system and ensure that flow rates are correct, giving added protection to valves, heat exchangers and additional boiler components.

Calculating Your Required Flow Rate

Flow rate measured in gallons per minute determines how much water your pump must circulate to deliver adequate heat throughout your system. The basic formula divides your total heat load in BTUs/hour by the number of temperature drop that you design for multiplied by 500. For most installations using a 20 degree temperature drop (most residential systems are designed for this) this basically means that every 10,000 BTU's would require approximately 1 GPM of water.

An 80,000 BTU (British Thermal Unit) heater in a 2,000 square foot home would need approximately 8 GPM of flow rate. Radiant floors typically require higher flow rates but lower temperature drop and baseboards may work with somewhat lower flow and greater temperature. Don't just guess at these numbers because undersizing by even 2 GPM can leave rooms uncomfortably cool during peak heating demand.

Understanding Head Pressure Requirements

Head pressure represents the force your pump needs to overcome friction in pipes, fittings, valves, and heat exchangers as water circulates through your system. Calculate this by multiplying the length of your longest circuit including both supply and return runs by a friction factor around 0.06 for typical residential installations with standard piping. A 200 foot circuit would need roughly 12 feet of head pressure to maintain adequate flow.

Two story homes or systems with lots of fittings and valves need more head than simple single level layouts with straight pipe runs. Most residential systems fall between 6 and 15 feet of head, though complex multi zone setups can push higher. OutdoorBoiler.com's technical team helps you calculate exact head requirements based on your specific piping configuration, taking the guesswork out of pump selection.

Learn About Piping Types for Heating Systems

Variable Speed vs Fixed Speed Technology

Variable speed ECM pumps represent the current standard for 2026 installations because they automatically adjust motor speed to match actual system demand moment by moment. When thermostats close in some zones reducing flow requirements, the pump slows down instead of fighting against closed valves. This intelligence prevents energy waste and reduces wear on mechanical components throughout your heating system.

Fixed speed and multi speed pumps still have a place in very simple systems where constant flow makes sense or in replacement situations where the existing controls aren't compatible with variable speed operation. These cost less upfront but operate at full power whenever they're running regardless of whether the system needs maximum flow or not. For new installations or major renovations, the energy savings of variable speed technology justify the modest additional cost within two heating seasons.

Material Selection for System Compatibility

Cast iron pump housings work perfectly for closed loop hydronic heating systems where water stays contained and doesn't need to be potable. The material handles heating system temperatures and pressures reliably while costing less than stainless or bronze alternatives. Closed loop systems with outdoor boilers connected to radiant floors or baseboard radiators use cast iron pumps almost exclusively.

Stainless steel or bronze construction becomes necessary for open loop applications where the pump contacts potable drinking water or in systems with particularly aggressive water chemistry. These materials resist corrosion better than cast iron but cost significantly more and aren't needed for standard outdoor wood boiler hydronic heating. Match your pump material to your specific system type instead of spending extra for corrosion resistance you don't actually need.

Getting Connection Sizes Right

Pump inlet and outlet connections must match your existing pipe diameter to prevent flow restrictions that kill system performance. The most common connections in residential shops are 3/4 inch or 1 inch, although you may see larger fittings of 1.25 or even 1.5 inches for larger systems in commercial settings. Even in the case of a 3/4 inch pump on a 1 inch piping system, that forms a restriction which negates any benefit from correctly sized pipe elsewhere.

There are different dimensional standards for PEX tubing, copper pipe and steel pipe so ensure you specify the actual outside diameter when comparing pump connections. Reducers and adapters will allow you to connect differing sizes if necessary, but every reduction will add resistance that your pump must overcome. Design your system with the same pipe size all around to gain maximum efficiency and make pump selection simple.

Review EPA Standards for Residential Wood Heating

Accounting for Glycol and Additives

Systems using propylene glycol antifreeze for freeze protection need pumps sized slightly larger than pure water systems because glycol increases fluid viscosity. A 30% (glycol) typical of outdoor boiler freeze protection might require 10-15 percent more pumping capacity than water. If you do not take this into consideration, your home will be underperforming in cold weather when you want to use it most.

Snow melt systems and other applications with high glycol concentrations face even bigger viscosity challenges. (Note: It is important to specify glycol content when choosing pumps; manufacturers can then recommend adequately powered models.) The viscosity effect is temperature dependent, and cold glycol mixtures are much thicker than warm ones (which might be important for systems that run in wide temp ranges).

Using Pump Curves to Verify Selection

Manufacturers publish pump performance curves showing the relationship between flow rate and head pressure for each model. Your GPM should be plotted on the horizontal axis and you head calculated to the vertical axis. Your pump of choice has a curve that is going through or close to this duty point, it will deliver the flow you want at the pressure your system wants.

Avoid pumps where your duty point falls way below their curve because they're significantly oversized and will waste energy. Pumps where your point sits above the curve can't deliver adequate performance and will struggle constantly. OutdoorBoiler.com provides pump curve data and selection assistance to ensure the model you choose actually matches your calculated system requirements instead of just guessing based on price or availability.

Special Considerations for Multiple Zones

Multi zone heating systems need careful pump sizing because total flow varies as zones open and close throughout the day. Some installations use a single large pump with zone valves that redirect flow, while others employ multiple smaller pumps dedicated to individual zones. Variable speed pumps excel in zone valve systems because they adapt automatically to changing demand.

Zone circulator approaches with dedicated pumps for each area provide more precise control and let you size each pump specifically for its zone's requirements. This costs more in pumps but can improve comfort and efficiency in complex layouts with very different zone sizes. Consider your system's complexity and budget when deciding between these approaches, knowing that either works well when sized correctly.

Signs Your Current Pump Is Wrong

Cold spots in your home despite the boiler running hot indicate insufficient flow reaching distant zones. Inordinate noise (rattling, buzzing, gurgling) indicates cavitation from oversize pump or air in the system. There is a high electric bill comparing with other homes of similar size which can indicate an old pump working nonstop at maximum rate.

Recurring pump maintenance failures or short service life is often a result of improper sizing that requires the pump to work harder than necessary all the time. If you’re changing out pumps every couple of years, rather than seeing them last 10 to 15 years, sizing or water quality is probably the problem. OutdoorBoiler.com's staff can review your current configuration and determine whether pump issues result from improper sizing, bad water treatment or installation.

Your Pump Selection Questions Answered

What size circulating pump does a typical home need? Most residential systems use pumps rated for 8 to 15 GPM with 6 to 12 feet of head pressure.

Are variable speed pumps worth the extra cost? Yes, energy savings typically recover the price premium within two to three heating seasons through reduced electricity use.

Can you use a larger pump than calculated? Not recommended, as oversized pumps waste energy and can create noise and flow balance problems.

How long should a circulating pump last? Quality pumps properly sized and maintained typically provide 12 to 18 years of reliable service.

Do outdoor boiler systems need special pumps? Not necessarily, but they must handle the higher temperatures and potential glycol mixtures in outdoor boiler applications.

Can you replace just the pump motor instead of the whole unit? Some models allow motor replacement, but complete unit replacement often makes more sense for older pumps.

Getting Professional Guidance on Pump Selection

Choosing the right circulating pump requires accurate calculations based on your specific system design, heating load, and piping configuration. Small errors in flow rate or head pressure calculations lead to pumps that don't perform well, wasting money on equipment that doesn't solve your problems. Professional sizing eliminates guesswork and ensures the pump you buy actually matches what your system needs.

OutdoorBoiler.com specializes in outdoor wood boiler systems and understands the unique requirements these installations demand. Their technical team has sized pumps for thousands of systems and can help you avoid the common mistakes that lead to poor performance or premature failures. Whether you're building new or upgrading existing equipment, accurate pump selection is crucial for system efficiency and reliability.

Ready to select the perfect circulating pump for your heating system? Visit OutdoorBoiler.com to explore quality pump options from manufacturers like Grundfos, get expert sizing assistance based on your specific requirements, and access the technical support that ensures your selection performs as expected. Don't guess on something this important when professional guidance is readily available.