By Eric Moshier – Certified Heater Mason, Third-Generation Mason, MHA Technical Committee Member, ASTM E1602 Masonry Heater Group Member
Masonry heater sizing starts with your home’s heat loss, not its square footage. At Solid Rock Masonry LLC in Duluth, Minnesota, Certified Heater Mason Eric Moshier, an ASTM E1602 committee member and MHA Technical Committee member with 800+ completed projects, sizes every heater the same way: run a free Manual J heat loss calculation at LoadCalc.net, convert that hourly number into a daily heat demand, and match it to the heat a firebox load of wood actually delivers. A full fire puts roughly 5,000 to 5,400 BTU into the house for every pound of dry hardwood, depending on the method used. On that basis the SR-13 (35 lb load) heats about 1,000 to 1,200 square feet, the SR-18 (60 lb) about 1,800, the SR-22 (65 lb) about 2,000, and the new SR-32 (80 lb) about 2,400, in well-insulated homes with 8-foot ceilings. SR Core DIY masonry heater kits run $5,000 to $13,600 and ship nationwide from Duluth, and site-built masonry heaters run $20,000 to $40,000. This guide shows the math, including the long-used bell heater rules of thumb and the European Kachelofen calculation method, so you can check any heater against your own house.
Why does masonry heater sizing start with a heat loss calculation?
Square footage tells you how big a house is. Heat loss tells you how fast that house leaks heat on a cold day, and that is the number a heater actually has to answer. Two houses with the same floor area can have very different heat loss depending on insulation, air sealing, windows, ceiling height, and climate.
The standard method is ACCA Manual J, the ANSI-recognized residential load calculation used to size heating and cooling equipment. LoadCalc.net is a free online calculator based on Manual J. It returns the whole-house heating load in BTU per hour at your local design temperature, which is one of the coldest conditions your house will see in a typical winter.
How do you run a heat loss calculation on LoadCalc.net?
Select your state or province, then pick the nearest city or airport so the program loads your local design temperatures. Enter the house dimensions, ceiling heights, wall, ceiling, and floor insulation, window and door areas, and how tight the house is. Use real numbers from your plans, not guesses, because every input moves the result.
Write down the heating load in BTU per hour. That single number is what we ask for when you call about a heater. If you are still at the design stage, the Solid Rock Masonry Heater Planning Guide walks through how the heat loss feeds into model selection, foundation, and chimney decisions.
What does a LoadCalc.net result look like for an 1,800 square foot house in Duluth?
We ran a typical 1,800 square foot house through LoadCalc.net to show how masonry heater sizing works with real numbers. The house is hypothetical, but every input is the kind of thing you will find on a set of plans:
- Location: Duluth Airport, Minnesota. LoadCalc loads a heating design temperature of -16 degrees F outdoors against 70 degrees F indoors.
- Single story, 30 x 60 feet, 8-foot ceilings, 14,400 cubic feet
- 2×6 walls with R-19 insulation and siding, R-50 attic, slab on grade with R-10 edge insulation
- 230 square feet of Low-E windows, a 40 square foot double-pane glass door facing south, and two solid wood entry doors
- Construction tightness rated good, four people, three bedrooms
LoadCalc returned a heating load of 33,034 BTU per hour. That is the peak rate on the coldest design hour, about 18 BTU per hour per square foot. Windows, the slab edge, and air leakage account for well over half of it.
Now turn that into daily heat. On the -16 degree design day, the house needs about 33,034 x 24 = 793,000 BTU. That day is rare. The National Weather Service lists the Duluth January normal at 1,669 heating degree days, an average temperature of 11.2 degrees F (NWS Duluth January climate summary). Scaling the LoadCalc result to heating degree days, this house needs about 9,200 BTU per degree day, or roughly 496,000 BTU on an average January day.
An SR-18 fired twice a day delivers about 655,200 BTU. That covers an average Duluth January day with about 30 percent to spare. On the handful of design-cold days, two fires come up a little short of the 793,000 BTU design-day demand. A backup heat source covers the gap, and a third fire is possible within the one-load-every-8-hours limit, though few owners ever need it. That is why the SR-18 is rated for about 1,800 square feet, and why it holds up in Duluth.
Can you estimate heat loss before you run the full calculation?
Yes, for a first look. Bell heater builders have long used a rule of thumb for heat loss on the coldest day with standard glazing. Eric first learned these numbers in a bell heater class taught by Alex Chernov, founder of Stovemaster and the mason who brought the Russian bell heater to North America. We still use them as a quick heat loss check:
| Construction | Heat loss on the coldest day |
|---|---|
| Super-insulated (R-30+ walls) | about 10 BTU/hr per sq. ft. |
| 2×6 walls, mineral wool or fiberglass (R-20) | about 20 BTU/hr per sq. ft. |
| 2×4 walls, fiberglass (R-10 to R-13) | about 25 to 30 BTU/hr per sq. ft. |
| Uninsulated older houses | 50 BTU/hr per sq. ft. and higher |
These are coldest-hour figures, and they run conservative. Our Duluth example house with 2×6 walls came in at about 18 BTU per hour per square foot on LoadCalc. Use the rule of thumb to start a conversation, then run the real numbers. Ceiling height, glass area, and air leakage can move the answer a long way in either direction.
Why can’t you compare Manual J BTU/hr directly to a masonry heater?
This is the mistake most masonry heater sizing advice gets wrong. A Manual J result is a peak rate: how many BTU per hour the house loses at design temperature. A furnace is sized to that peak because it makes heat on demand, hour by hour.
A masonry heater does not work that way. It is a radiant heat storage appliance. You burn a full load of wood hot and fast for 2 to 3 hours, the masonry absorbs that energy, and the heater releases it slowly over the next 12 to 24 hours. Our guide to how a masonry heater works explains the burn, the heat exchange channels, and the slow release in detail. For sizing, the point is simple: a heater’s output is a daily quantity of stored heat, not an hourly firing rate.
How do you convert heat loss into a daily heat demand?
Multiply your design heat loss by 24. A house that loses 24,000 BTU per hour at design temperature needs about 576,000 BTU over a full design day. Then compare that daily demand to the daily output of the heater with two fires a day, which is normal on the coldest days.
You can also run it the other way. Divide a heater’s daily output by 24 to get its average hourly delivery, and compare that to your Manual J number. Either way, you are comparing a day to a day, which is the only fair comparison for a heat storage appliance.
How much heat does a pound of firewood put into the house?
Everything in masonry heater sizing comes back to BTU, and the BTU come from the wood. A masonry heater’s output is set by how many pounds of wood the firebox burns per fire and how much of each pound’s energy ends up in the house.
Dry wood holds about 8,500 to 8,600 BTU per pound, and the species matters less than most people think. The USDA Forest Products Laboratory, in How to Estimate Recoverable Heat Energy in Wood or Bark Fuels (Ince, 1979), puts the average at about 8,500 BTU per oven-dry pound regardless of species. Its survey table lists hardwoods such as oak, maple, ash, and hickory at roughly 8,100 to 9,400 BTU per pound, with softwoods like lodgepole pine and Douglas-fir in the same range.
So a pound of oak, maple, or birch and a pound of pine or spruce carry about the same heat. The difference is density. Hardwood packs more pounds into the same firebox, which is why masonry heater sizing is figured in pounds of wood per fire, not cords or armloads. Firewood is never oven-dry, and no heater captures every BTU, so the gross number has to be discounted.
The rule-of-thumb output calculation
The bell heater rule of thumb starts with the 8,600 BTU per pound for dry wood, multiplies by 0.8 to account for the moisture still in seasoned firewood, and then multiplies by the heater’s efficiency. The rule as it was taught uses 85 percent, the efficiency of a well-built bell heater. Across all heater styles, we use 78 percent as an average:
8,600 x 0.8 x 0.78 = about 5,370 BTU delivered per pound of wood
Multiply that by the pounds burned per day and divide by 24 for the average hourly output. The worked example that comes with the rule is a heater with a firebox that holds 60 lb of hardwood, fired twice a day, the same load as our SR-18. Two 60 lb fires burn 120 lb a day. At the 85 percent bell efficiency, that is 120 x 5,848 = about 701,800 BTU per day, or about 29,200 BTU per hour averaged over 24 hours. At our 78 percent average, the same 120 lb delivers about 644,000 BTU per day, or about 26,800 BTU per hour, right in line with the published SR-18 rating.
The European Kachelofen calculation
The European calculation method for one-off tiled and mortared stoves, drafted by CEN Technical Committee 295 in 2005 and developed into the standard published as EN 15544, sets the maximum fuel load from the heat output the house needs. In the 2005 working draft we use, the maximum load in kilograms equals the nominal heat output in kilowatts times the nominal heating time in hours, divided by 3.25. Put another way, the method credits each kilogram of wood with about 3.25 kWh of delivered heat, which is about 5,030 BTU per pound.
The same draft covers wood-fired tiled stoves with maximum loads from 10 to 40 kg (about 22 to 88 lb) and nominal heating times from 8 to 24 hours, so every SR Core firebox from the SR-13 to the SR-32 falls inside its range. It also recognizes partial heating, where the stove is designed to carry only part of the calculated heat load, and it sets the minimum load at 50 percent of the maximum.
Which number should you use?
All three land within about 7 percent of each other. The CEN method credits about 5,030 BTU per pound, our published SR Core ratings use about 5,250, and the rule-of-thumb formula at a 78 percent average efficiency gives about 5,370. For sizing, we work from the published ratings.
Which SR Core heater fits my house: SR-13, SR-18, SR-22, or SR-32?
These are the SR Core ratings and the starting point for masonry heater sizing. The heating areas assume well-insulated Energy Star construction, 8-foot ceilings, and a cold northern climate like ours in Duluth. Treat them as a starting point, then confirm with your heat loss number. The SR-13, SR-18, and SR-22 figures are the published ratings on our SR Core kits page. The SR-32 figures come from its Grundofen calculation.
| Model | Firebox width | Fuel per fire | Output, 1 fire | Output, 2 fires | Avg. BTU/hr, 2 fires | Typical heated area |
|---|---|---|---|---|---|---|
| SR-13 | 13 in. | 35 lb | ~183,750 BTU | ~367,500 BTU | ~15,300 | ~1,000 to 1,200 sq. ft. |
| SR-18 | 17 in. | 60 lb | ~327,000 BTU | ~655,200 BTU | ~27,300 | ~1,800 sq. ft. |
| SR-22 | 22 in. | 65 lb | ~341,000 BTU | ~682,000 BTU | ~28,400 | ~2,000 sq. ft. |
| SR-32 | 32 in. | 80 lb | ~398,000 BTU | ~796,000 BTU | ~33,200 | ~2,400 sq. ft. |
Fuel loads are rated at a maximum of one full load every 8 hours. Most homes run on one fire a day in mild weather and two on the coldest days, one in the morning and one in the evening. A third fire is possible within the 8-hour limit, but few owners ever need it.
The SR-13 suits smaller, tight homes, cabins, and additions of about 1,000 to 1,200 square feet, depending on insulation and location. The SR-18 is one of our most frequently ordered systems for homes in the 1,500 to 1,800 square foot range. The SR-22 fits homes up to about 2,000 square feet and larger open floor plans where the heater sits centrally. Each is available as a Hybrid or Cast core, with a black oven (BO) or white oven (WO) option. Full specifications and pricing are on the SR Core kits page.
Why do SR Core masonry heater kits come in four sizes?
Most masonry heater kits on the market are built around a single, one-size-fits-all core. The same firebox goes into a 1,000 square foot cabin and a 2,400 square foot home, and the house has to adapt to the heater. That works against everything in this guide. Our SR Core kits come in four primary sizes to cover the heat load of the house. A firebox that is too big for the house overheats the rooms on a full load, and one that is too small leaves you short on the coldest days.
Masonry heater sizing should run the other way. SR Core kits come in four firebox widths, 13, 18, 22, and 32 inches, so the fuel load matches your heat loss instead of the other way around. Each size is available as a Hybrid or Cast core, with black oven, white oven, cook top, and heated bench options, so you choose the size for the house and the features for the way you live.
Germany and Austria have sized heaters this way for a long time. Heinz Maresch’s 1972 Kachelgrundofen practitioner’s guide, published by the Informationsstelle Kachelofen in Stuttgart and translated into English by Norbert Senf, draws on German rules from 1942 and the DIN 18 899 standard of 1955. Its first step is the heat loss of the room, and its first rule is that the stove must meet that heating requirement with the most efficient use of fuel, without being over-fired. The heat loss sets the warm surface area the stove needs, and that sets the firebox and the length of the flue channels.
Many German and Austrian heaters today are built around certified fireboxes in a range of sizes, with flue channels added to balance each heater to the house it serves. That is the approach we follow. Our design target for every SR Core heater is 80 percent efficiency or better, reached through the core design itself or by adding a heated bench to extend the heat exchange.
For smaller spaces we go smaller still. Our masonry cook stoves use a compact SR-9 firebox with heat exchange channels built into the masonry, so they store heat like a heater and add meaningful radiant heat to rooms and cabins under about 600 square feet. If your heat loss falls between sizes or outside them, we will design around it rather than sell you a core that does not fit.
What is the SR-32?
The SR-32 is our largest SR Core unit, built to replace the big open fireplace that architects often design into a home. Its 32-inch-wide firebox and wide glass door give the same large fire view, but it burns hot, clean, and efficient, and it actually heats the house, unlike most fireplaces that are there only for looks. The SR-32 is a calculated, German-style Grundofen design: the gases leave the firebox and wind through a long run of channels before they vent out the top. The firebox takes an 80 lb load. The core is 60 inches wide and 23 inches deep, and with a 5-inch masonry veneer it finishes about 70 inches wide, 33 inches deep, and 95 inches tall. With the 8-inch clearance to combustibles above it, the SR-32 needs a ceiling of at least 103 inches, so it is designed for rooms taller than 8 feet. The SR-32H kit, top-vented with no oven, is $11,430 on our kits page.
How do the three sizing methods compare for each SR Core model?
Here is every SR Core size run through all three methods. The table shows the average heat delivered per hour over 24 hours with two full fires a day.
| Model | Fuel per fire | CEN method (~5,030 BTU/lb) | SR Core rating (~5,250 BTU/lb) | Rule-of-thumb formula at 78% (~5,370 BTU/lb) |
|---|---|---|---|---|
| SR-13 | 35 lb | ~14,700 BTU/hr | ~15,300 BTU/hr | ~15,700 BTU/hr |
| SR-18 | 60 lb | ~25,200 BTU/hr | ~27,300 BTU/hr | ~26,800 BTU/hr |
| SR-22 | 65 lb | ~27,200 BTU/hr | ~28,400 BTU/hr | ~29,100 BTU/hr |
| SR-32 | 80 lb | ~33,500 BTU/hr | ~33,200 BTU/hr (calculated) | ~35,800 BTU/hr |
With one fire a day, cut each figure in half. In the metric terms of the CEN method, the SR-18 fired twice a day is about a 7.4 kW heater and the SR-32 about a 9.7 kW heater.
How much mass and surface should a masonry heater have for its firebox?
Sizing does not stop at the firebox. The mass has to store the fire’s heat and still warm up enough to give it back.
How much mass should a masonry heater have?
An older bell heater rule of thumb caps the mass at about 300 lb of masonry per pound of wood for heaters fired twice a day, and 150 lb for heaters fired once a day. Our experience does not support that limit. A typical SR-18 with a 5-inch stone finish weighs about 13,000 lb, well above the 9,000 lb that rule allows for a 60 lb firebox fired once a day, and it heats the house well on one fire a day in mild weather and two on the coldest days. What matters is that the heat can get through the shell to the room, which comes down to wall thickness, covered in our how a masonry heater works guide.
ASTM E1602 and the Masonry Heater Association set the minimum at 800 kg (about 1,760 lb), not counting the chimney and foundation. Every SR Core heater is well above it. A stone veneer and a heated bench add mass, which is one reason we can finish an SR Core heater in heavy fieldstone without hurting its performance.
Surface area and heat output
Heat leaves a masonry heater through its outside surface, mostly as radiant heat. More warm surface spreads the same heat across more of the room at a gentler temperature. A heated bench is the simplest way to add warm surface without adding height.
How do ceiling height and climate zone change the size?
The ratings above assume 8-foot ceilings. Taller walls and vaulted ceilings add exterior wall and glass area, which raises heat loss, so enter your real ceiling heights in LoadCalc rather than adjusting the square footage by eye.
Climate works the same way. Duluth sits in St. Louis County, which Minnesota’s energy code places in climate zone 7. The same house in a milder climate has a lower design heat loss, so a given heater covers more floor area there and less in a colder one. Because LoadCalc pulls your local design temperature, the heat loss number already accounts for climate. That is why masonry heater sizing starts from heat loss and not from a square footage chart.
What happens if a masonry heater is too big for the house?
Oversizing is mainly a comfort and fuel problem. A masonry heater is designed to burn a full charge of wood hot and fast, which is why the EPA describes masonry heaters as storing heat from rapidly burning fires. When the heater is bigger than the house needs, a full load stores more heat than the rooms can use, the house runs too warm, and owners start burning smaller loads than the heater was designed for. A smaller load still burns clean as long as it burns hot. The catch is heat: the standard rule is not to burn less than half the maximum load, because below that the heater gives very little heat back to the house. The European CEN method sets the same floor, a minimum load of 50 percent of the maximum.
A properly operated masonry heater does not produce creosote, even when it is oversized. In more than 40 years as a mason and 25 years building masonry heaters, this is what we have seen. A masonry heater is never dampered down. It burns with the air wide open until the main flames are done. Once the fire is down to coals, the air can be cut to about half, and it is closed when the fire is out. Creosote comes from incomplete combustion, and that happens when the air is choked down while there is still a lot of wood left to burn and the firebox temperature drops.
What controls how cleanly a heater burns is the design of the firebox: its size and proportions, how much combustion air comes in, and where that air is delivered. Solid Rock firebox doors have an air frame that delivers about 20 percent of the air at the base of the fire and about 80 percent at the top. Another proven method, credited to Norbert Senf, brings about half the air in through a small grate at the front of the firebox and half in at the back. In our experience, both approaches burn clean.
We keep SR Core fireboxes 18 inches deep, because typical firewood is cut 16 to 18 inches long. The only exception is a see-through firebox, which runs about 23 inches deep. In our experience, see-through fireboxes do not burn quite as cleanly or as efficiently as an 18-inch firebox with a firebrick back wall.
Is it better to undersize a masonry heater?
Undersizing slightly is still the better choice, as long as the house has a backup heat source such as hydronic floor heat, electric baseboard, or forced air. A slightly undersized heater will probably not carry the whole load on the coldest days, and the backup covers the rest. We size every heater to the house and its heat requirement, but many houses today are simply too big for one heater. Once a house gets above about 2,000 square feet, it is hard to heat with a single heater, and we typically recommend two. Sometimes two heaters fit the budget and sometimes they do not. Two heaters also means two fires a day in two different heaters on the coldest days, which is real work. We do it at our own house every once in a while, so we know. Our masonry heater use and care guide covers how to fire a full load correctly.
How does an open or compartmentalized floor plan change placement?
Placement is the other half of masonry heater sizing. Radiant heat travels in straight lines from the warm masonry surface to the surfaces and people that can see it. If you cannot see the heater, you do not feel the heater. In an open floor plan, a centrally placed heater warms the whole main floor directly, and the SR-22 and SR-32 in particular work well as the centerpiece of a large open room.
A compartmentalized plan with closed rooms and hallways is harder. Place the heater on an interior core wall where several rooms can see it, keep doors open during the heating season, and expect back bedrooms and upstairs rooms behind closed doors to run cooler. Our planning process starts with your floor plan for exactly this reason.
When do two smaller heaters beat one large one?
Two smaller heaters make sense when one heater cannot see the rooms that need heat. Common cases are two-story homes with closed stairwells, long single-story homes with wings at each end, and plans where the living spaces are split by a central core of bathrooms and closets.
Two heaters also let you fire only the side of the house you are using. We have built stacked masonry heaters pairing a 13-inch and a 22-inch firebox for this kind of layout. When the heat loss is high and the plan is open, one SR-32 can replace two smaller heaters. For anything beyond that, our site-built custom masonry heaters cover Finnish Contraflow, Russian Bell, and Swedish 5 Run designs.
Do the same sizing rules apply to a Tulikivi soapstone heater?
Yes. Solid Rock Masonry also installs Tulikivi soapstone heaters, built in Finland. A Tulikivi is a radiant heat storage appliance just like a site-built masonry heater, so masonry heater sizing works the same way: start from your LoadCalc.net heat loss, convert it to a daily heat demand, and choose the Tulikivi model whose rated output fits. Our Tulikivi soapstone heaters page covers the models we install.
Does envelope quality matter more than square footage?
Yes. A tight, well-insulated 2,500 square foot house can need less heat than a drafty 1,500 square foot farmhouse with single-pane windows. The rule-of-thumb heat loss table above shows the spread: an uninsulated house loses five times as much heat per square foot as a super-insulated one.
This is why we push clients to fix the envelope before masonry heater sizing is final. Air sealing and insulation often let you drop a size, which lowers the kit cost, the foundation, and the wood you burn every winter. Our cost analysis of whether masonry heaters are worth it shows how the operating savings add up over ten years.
How much does a masonry heater weigh, and what does that mean for the structure?
A masonry heater is heavy by definition. ASTM E1602 sets a minimum mass of 800 kg, about 1,760 lb, not counting the chimney and foundation. The firebox core is only part of the weight. The brick or stone shell around it stores and radiates much of the heat into the room, so it belongs in the total. A typical SR-18 stands 7.5 feet tall, 50 inches wide, and 33 inches deep, with about 104 square feet of outside surface:
- SR-18 with a brick finish: about 8,000 lb (3,600 kg)
- SR-18 with a 5-inch stone finish: about 13,000 lb (5,900 kg)
- SR-22 with a brick finish: about 8,600 lb (3,900 kg)
- SR-22 with a 5-inch stone finish: about 13,800 lb (6,300 kg)
A heated bench or a masonry chimney adds to those numbers. Every heater needs its own foundation. Solid Rock Masonry specifies 4,500 psi concrete or better, 8 inches deep, with 1/2-inch rebar at 12 inches on center. Clearances, hearths, and inspection requirements are covered on our masonry heater building codes page.
Masonry heater sizing FAQ: what do people ask most?
Can one masonry heater heat a whole house?
Often, yes, if the heater is sized to the heat loss and placed where the living spaces can see it. Open, well-insulated single-story and story-and-a-half homes are the best fit. Closed floor plans and upper floors behind closed doors usually need a second heater or a small backup source.
How many BTU does a masonry heater get from a pound of wood?
Roughly 5,000 to 5,400 BTU delivered per pound of seasoned wood. The European CEN calculation credits about 5,030, the SR Core ratings use about 5,250, and the rule-of-thumb formula at a 78 percent average efficiency gives about 5,370.
How do I calculate masonry heater output?
Multiply the pounds of wood per fire by the BTU delivered per pound, then by the number of fires per day, and divide by 24 for the average hourly output. Two 60 lb fires at about 5,250 BTU per pound deliver roughly 630,000 to 655,000 BTU a day, or about 27,000 BTU per hour.
How many fires a day does a masonry heater need?
One fire a day is enough in mild weather. On the coldest days, two fires a day is normal, one in the morning and one in the evening, and a third fire is rarely needed. Each fire burns for 2 to 3 hours. SR Core fuel loads are rated at a maximum of one full load every 8 hours.
Is it better to oversize or undersize a masonry heater?
Undersize slightly, as long as the house has backup heat such as hydronic floor heat, electric baseboard, or forced air. A slightly small heater may not carry the whole load on the coldest days, and the backup covers the rest. An oversized heater overheats the house on a full load, so owners end up burning smaller loads than it was designed for.
Can I size a masonry heater from my furnace BTU rating?
No. A furnace rating is an hourly firing rate, and it may not match your house’s actual heat loss. Start from a Manual J heat loss calculation at LoadCalc.net and convert it to a daily demand.
What size is the SR-32 masonry heater?
The SR-32 has a 32-inch-wide firebox that takes an 80 lb load, about 796,000 BTU a day with two fires, or about 33,200 BTU per hour averaged over 24 hours. It suits homes of about 2,400 square feet in well-insulated construction. It finishes about 70 inches wide, 33 inches deep, and 95 inches tall, and needs a ceiling of at least 103 inches.
What if my house is larger than 2,000 square feet?
Above about 2,000 square feet, one heater has a hard time heating the whole house, and we typically recommend two. Check the heat loss first, because a tight, open house may still work with an SR-22 or an SR-32. Two heaters are not always in the budget, and two fires a day in two heaters is real work, so backup heat often carries part of the load instead.
Will Solid Rock Masonry check my masonry heater sizing?
Yes. Send your floor plan and your LoadCalc.net heat loss number, and we will recommend a specific model and placement before you order anything.
Get a sizing review from a Certified Heater Mason
The fastest route to correct masonry heater sizing is to send us two things: your floor plan and your heat loss number. We will tell you which SR Core model fits, where it should sit, and whether one heater or two makes more sense. Call 218-343-2978, email eric@solidrockmasonry.com, or use our contact page.
Solid Rock Masonry LLC, 5347 Howard Gnesen Road, Duluth, MN 55803.