Heating a Renovated Farmhouse
I recently purchased an old double-brick farmhouse in a rural area in Ontario, Canada (climate zone 6 I believe). I am planning an extensive renovation of the house with the goal to get it fairly airtight and well insulated, within reason. The house is 2 stories, roughly 1200 sqft. I am also planning a fairly big addition within the next 5 years or so, probably adding an additional 1500 sq ft, again built to a good standard when it comes to insulation and air-sealing. I am fairly experienced with renovating houses, so at the very least I will be GC-ing the project, and likely doing a lot of the work myself (except drywall and electrical lol).
I am trying to decide on a heat source for the house. For a number of reasons I am leaning heavily towards hydronic radiant-floor heating. I rarely use A/C in the summer so not worried about losing the ducts, I have allergies, and I find in-floor heating to be very comfortable in other houses I have stayed in. Since we are gutting the house to the joists (and then building a new addition), the install should be about as straightforward as it can be.
The property is rural with about 20 acres of forest, and with no natural gas service, so that leaves me with electric, propane, or outdoor wood for the boiler. Not really considering a heat pump (upfront cost, skeptical about them in very cold climates although I understand that they have come a long way in the past few years), but could be talked into it.
I have done some preliminary research and have a vague idea of the kind of system I want to install, but am hoping to get some feedback on any trouble I may run into, as well as some specific questions about my proposed system.
My end-goal is to heat the existing house, the addition, and potentially a large garage with an outdoor wood boiler powering hydronic heating in all structures. There would also be a backup boiler in the house in case we have to go on vacation or get injured and can't process firewood. The wood burner is not really about saving money/efficiency, but more of a personal/lifestyle choice since I like processing wood and like the idea of being more self-sufficient.
That being said, the upfront costs of the OWB are fairly high, and I won't have time to mess around with firewood while also trying to manage the renovation, the addition, and garage build. So I am considering installing the heating system in stages, something like this:
Stage 1: install "backup" heating source in existing renovated structure.
Stage 2: install "backup heating source in the addition
Stage 3: install OWB to be used by the main house and the garage
Apologies for all the background info, but here are my questions.
- General feedback on the idea of having OWB as the primary and then having a secondary for times when we are away or not using wood for whatever reason.
- Electric vs Propane for the backup/initial boiler. Electricity is roughly $0.10/kWh (time of use pricing so it varies throughout the day), propane was roughly $0.97/L in the area in 2023. I am leaning towards electric since I don't like the idea of having a large propane tank and deliveries and all that, but have not done the math to see which would be more cost-effective.
- Oversizing the backup/initial boiler to allow for the future addition. I understand that there are problems with oversizing your boiler, but would it be fine for a few years before doing the addition? Or would it be better to have the boiler be sized appropriately for the existing house, and either add a second boiler for the addition, or go straight to OWB and have an undersized backup.
Thanks in advance, and will try to answer any questions if it helps.
Comments
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I presume oil is not an option? At your prices, your propane and electric are surprisingly close in cost per kW. As I see it in a rural area, the advantage of propane is that you can probably run it with a generator when the lights go out. Can't do that with electric.
All that said your approach seems reasonable to me, except for one thing: I'm not at all sure you will be able to get enough heat out of the radiant floors alone, and so I'd be very much inclined to do the radiant floors, yes, but also inclued some panel radiators to add additional heat when needed, and to give the ability to more rapidly raise the heat in specific spaces, if you wanted to. You need to do some real numbers on heat loss.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
Thanks @Jamie Hall , appreciate the feedback.
Oil is theoretically an option, but for seemingly political reasons it is being phased out in Canada. You won't find many new builds with oil, and I suspect it will be harder to get it serviced and fueled as the years go by.
Agree, propane is a bit better in case of power-outage, but with the eventual OWB would not be a problem.
Are the online heat loss calculators sufficiently accurate? Or is it worth consulting some kind of engineer to get a more accurate figure. If so, who should I be looking for. I have a background in engineering, so I'm not afraid of math, but not specifically trained in anything like this.
As well, any thoughts on the question of oversizing the boiler initially vs. installing a second boiler when the addition gets built?0 -
Everything you mentioned is possible.
The first step is a room by room heat load calculation. Both for existing rooms and future additions.
This is the only way to size everything. Boiler, piping, pumps, heat emitters.
If you find some areas with heat loads over 25- 27 btu/ sq ft, you will need supplemental heat in those areas.
Personally I would use panel radiators sized for radiant temperatures in all bedrooms. Really not a lot of benefit to radiant floors under beds and bedroom furniture. Radiant ceilings and walls are also options.
OWF need to be separated from you entire system with a heat exchanger in my opinion.
Backup boiler should be a modulation mod con type.
Piping and wiring ideas here.
https://www.caleffi.com/sites/default/files/media/external-file/Idronics_10_NA_Hydronics%20for%20wood-fired%20heat%20sources.pdf
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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+1 on getting a handle on the heating load first before any equipment selection. Well sealed and well insulated places tend to be under 10BTU/sqft heat load so you have to watch how you do any floor heat as it will never feel warm.
I went a similar route many moons ago with floor heat and mini split. One thing I didn't realize is that without a proper central air filter, even with an air tight place, there is actually much more dust. This makes sense in retrospect, I will definitely be replacing my wall mount mini splits with a ducted unit when they die to get better filtering.
This is a decent on-line heat loss calculator you can use to get a handle on base load:
They also host an extensive library of cold climate heat pumps, in Ontario energy prices, a heat pump is about 1/2 the operating cost of propane:
https://ashp.neep.org/#!/product_list/
No matter you main heat source, in rural area with long power outages, you will still need a backup that does not require power, something like a pilot operated fireplace or a through the wall vented propane heater. These should be sized to keep your place from freezing.
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In what blissful climate can you heat even a well insulated house for 10 BTUh per square foot? Rural Ontario near Havelock, where some of my relatives live? Where a warm January day is one where it gets above zero Fahrenheit with no wind? Um… I don't think so.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
Over the years on the Coffee with Caleffi series we have covered a number of actual projects in upstate NY, Vermont, and Maine, both new and remodels that fall in the 10- 15 btu/ sq ft range. It is certainly possible in Ontario.
Green Builder magazine has covered net zero homes with double digit low loads also.
Possibly even grant money to help you attain those numbers?
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
@hot_rod thanks for the advice, and for that document, been looking for something with this level of detail but did not know where to look.
As for whether I can get it to 10-15 btu range will remain to be seen, although it may be a challenge with this particular building.
There are usually grants available for these kinds of remodels in Ontario, especially when it comes to things like replacing the windows. Given the poor condition of the house currently I should be able to get the max of whatever grants are offered at this particular time, since many of them seem to be based on how much you improve the existing building.
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May I humbly point out that we don't know just where in Ontario we are working here? Conditions near Toronto, say, or Waterloo or Windsor are kind of like parts of upstate New York or Vermont, true. Conditions near, say, Peterborough are a bit chillier — like about 10 degrees Celsius chillier — and that's still the southern part of the Province. But get a little more rural… perhaps Long Lac or Thunder Bay or Kenora… Sudbury…
Good luck reaching 10 BTUh per square foot.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
Its around 35 min northeast of Kingston. So not super cold, but not balmy either.
The calculator @Kaos provided put me around 35k btu, although a lot of estimation done on my part since I don't have exact measurements for a few things.
One thing no one has really commented on yet was my question about oversizing the unit to accomodate a future addition, let's say 5 years down the road. Is it better to get a properly sized unit and either upgrade it or add a second unit for the addition? Or for that relatively short timespan there are ways I can mitigate by adding a buffer tank or something to reduce the short-cycling you can get with an oversized boiler. The addition would probably double the square footage
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It's all about the building shell. Spray foam really knocks down infiltration numbers, especially with old framing.
Glass is another big loss area.
The Cold Climate Housing Research Center in Fairbanks has done so low btu/sq ft homes. Your probably not looking at R-80 walls however I would say 10 is achievable, but not practical.
Shoot for 10, if you get to 15, you would call that a win, I suspect?
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
The building is already fairly small and double brick with no insulation, so I'm hesitant to put 8 inches of insulation and lose 100 sq ft of floor space. There will be some tradeoffs being made.
I'm a little averse to spray foam since I can't install it myself, so I am thinking of doing 1.5 inch R6 rockwool comfortboard, and then 2x4 interior framing with more rockwool comfortbatt R14, then air-seal as best I can.
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You may want to consider the flash-and-batt method for best air sealing. 2" or so of spray foam, then the 2x4 framing with the batts.
That minimizes the cost of spray foam but maximizes its air sealing benefit. However, you must be careful in cold climates to make the foam layer thick enough to minimize condensation, and if using closed cell foam you must allow the wall to "dry to the inside" so that vapor doesn't get trapped inside the wall.
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Since no one answered your question, I will.
I don't see an issue using one boiler for the whole thing especially since you will have wood as a backup.
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The hard part is dealing with the old brick. I would read though here, @jesmed1 has the one of the better approaches (wall 2):
If you offset the framing by about 1.5" and fill the gap with spray foam, you will get a decent thermal break and won't add all the much depth to your wall.
That is still close to an R20 wall, so not bad for an old house.
For the new build, you have many more options, no need for spray foam there. You can go with a simple wall such as 2x6+R5 rigid or 2x8 24"OC.
Once you get the details sorted out you can see where you end up on building load but I doubt it will be anywhere near needing multiple boilers. With heat pumps, you are probably better for going for two units, one for the old section and one for the new, otherwise it will be hard to integrate ducting.
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Thank you for the location! No, by Ontario standards your area isn't all that cold — but by most of US standards it's downright arctic. Take what some of us say about how much heat you need with a somewhat skeptical attitude!
Particularly with heat pumps. If you were to decide to go with a heat pump — which I wouldn't recommend in your climate — be sure to get an iron-clad guarantee that the heat pump chosen will, in fact, be able to heat the house to — lets say 25 C — with an outdoor temperature of -30 C (the coldest I've seen in Peterborough). And I do mean iron-clad — it it can't do it, he rips it out and replaces it with a boiler and hot water heat. At his expense. There's a lamentable tendency to talk mighty tall, but have a little trouble with the walk…
(Sorry, heat pump enthusiasts, but this isn't the wilds of New Jersey we're looking at here).
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
-30C is doable but output suffers, many units out there, this is just one. You would want a backup heat strip for those very cold days.
https://ashp.neep.org/#!/product/190260/7/25000/95/7500/0///0
Kingston has a 99% design of -18.5C, a bit north it is a colder but not much, so any -30C days are pretty short. The operating cost of this backup heat during for those rare polar vortex day is pretty small. The rest of the time it is cheaper than propane.
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Thank you all for all the great insight. Sorry to keep harping on this point but my question about using multiple boilers is not because of the expected load, I'm sure a single boiler can handle it. However, since I am building a large addition in a few (3-5) years, effectively doubling the square footage, I am wondering if I should oversize the boiler now in preparation for the addition, or go with a smaller boiler now and upgrade or augment down the line when the new addition is built.
I have some other thoughts about the spray foam and about heat pumps but will leave it until I can put this boiler question to rest first
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Until you can tell us a projected total heat load it is hard to give you a good answer
Two boilers gives you redundancy and 20-1 turndown and all the btu you need.
Or a hp and boiler for a dual fuel system.
Often $$ comes into the decision
Spend generously on the shell upgrades, it’s the gift that keeps on giving
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Common small boiler is 85k BTU, so it will take a heck of an addition to max it out.
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Thanks again for all the help. Will update with more accurate heat load in a few weeks/months as I begin demolition of the house interior
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One helpful way to look at some of this is to work out heating costs.
Say your place ends up at 35k heat load.
Kingston is 6500 heating degree days (F). Design from earlier was around 2F, so ~70F delta.
35000/70=500BTU/degF
500BTU*6500HDD*24H=780therms
If that is supplied by a 90% boiler from propane
780therms/0.91 (therms/gall)/0.9 (efficiency)= ~950gallons or 3500L
At about 0.7$/L that is $2500/year in heating fuel.
You kind of want to get that heat load down, there is real ROI especially since you are doing a full gut reno. So as @hot_rod said, "shell upgrades, it’s the gift that keeps on giving". 10BTU/sqft starts to sound much better :)
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Given the level of renovation and addition that you are doing and your interest in wood-heat, do not do an OWB (outdoor wood boiler). They are very costly and a huge waste of resources, time and human energy. You have the option to design a very nice area indoors for a wood gasification boiler and mod/con back-up fuel heating plant. For the solid fuel heating you would need to plan for a significant amount of heat storage in the form of buffer tanks. Fuel management is a big part of wood heating. For a gasification unit dry wood is critical! OWBs require an inordinate amount of firewood and for these, people often use substandard fuel i.e. wet/poorly seasoned. Harvesting all of that fuel and the time spent feeding the boiler is where the human input is wasted. Use the Caleffi Idronics manuals to help design for combination inputs of indoor solid fuel burners and high efficiency mod/con boilers. Do not skimp on the building envelope improvements. Hydronic radiation will provide the best options (panel rads, floor, ceiling, wall radiation) for heat distribution. If your buildings end up anything close to only requiring 10BTU/SqFt. you'd better be providing for good air exchange with HRV (heat recovery ventilation).
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@psb75 thanks for the tips. What kind of moisture content is idea for a gasifier? The property has plenty of wood so there's no shortage, although I can see how the labour of stacking it and managing the OWB would be tiresome after a couple years.
I like the idea of leaving the combustion outside of the house, for safety and since it would avoid having to drag firewood into the mechanical room. Possibly build a little outbuilding for the wood burner if I was going the gasifier route. As well, the basement (which will be entirely for mechanicals) is a bit small, so between buffer tanks, conventional boiler, and the gasification boiler will be getting tight.
I was thinking it would make sense to build the HRV/ERV into the addition, rather than the original structure.
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I had a 40kw gasifier in my shop. I started with a 160, switched to a 300, and ended up with a 500 gallon buffer tank. A thorough cleaning and brushing every two weeks, even with good, hard, dry wood. Wood burning is a chore.
Don’t buy into the myth that green wood burns better or lasts longer!
Once again, knowing the heat load is critical for sizing solid fuel burning equipment.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
If you are doing all the work to gather the wood, at least enjoy the ambiance of the flame. I've seen this used in a low load project before:
The one issue is they need pumps powered to burn, so you have to plan on providing at least some power backup.
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Thats a cool product. I'd probably add a supplemental airtight wood stove in the addition though if I wanted the ambiance... And a wood-fired sauna next to the river. I love wood 🤣
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I love wood burning and fuel harvesting and managing. My dream wood burning unit—that INCLUDES storage and best combustion efficiency— is very, very old technology. A masonry heater. AKA Russian/Finnish stove. It uses 1/2 the amount of firewood as a good wood boiler. Non electric. No circulating water.
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Until 3 years ago we have always had a wood burning component in all our homes. Even growing up as a kid. Being a city dweller now, I miss all the aspects of heating with solid fuels. the harvest, splitting, burning and tending, even the cleaning ritual was satisfying.
I sold and installed a number of gasification units. Zenon at New Horizons is the guru of Euro based gasification products.
The ISH show in Frankfurt is a great place to see wood burners from around the world. Austria rents one entire hall to showcase all the products they manufactures.
The one that caught my eye when we had the farm was a gasification burner that would hold an entire 5' round bale. So many of those bales rot away in the fields.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0
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