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Furnace size for a 1950s Toronto Bungalow

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Sr. Member
Mar 13, 2017
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Furnace size for a 1950s Toronto Bungalow

Question for the experts:

Just got quoted for a 40000 BTUH Goodman 96% EFF 2 STG Gas furnace on a 1200 SF bungalow with 900 SF of finished basement.

That seems rather small to me? What says the experts?

1950s brick/brick with 20yr old windows and original insulation rental property.

TIA for any comments.
44 replies
Member
Dec 6, 2020
281 posts
255 upvotes
Too many variables to say. You need to have a load calculation (ACCA Manual J) done to calculate the correct size of equipment for the building.
Deal Addict
Jan 19, 2011
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I have a 3000 square foot (on first and second floor) double brick Victorian home, uninsulated and installed an 85k BTU furnace which has no issue at all keeping the place heated.

I did the design calculation myself from a technical sheet posted on the CMHC website (no longer available) Actual design requirements were 57K BTU if I recall, I can send you the link to my blog which has the actual calculation.

40k btu is more than sufficient for your house, and is likely the smallest available furnace anyway.
"The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end; there it is."
Just a guy who dabbles in lots of stuff learning along the way. I do have opinions, and readily share them!
Deal Addict
Jun 16, 2009
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I concur @fieldhousehandyman . We recently installed 60K in 3000 sq ft home AFTER homeowner got his heat loss calculations done. Even though house was 20+ years old, it was very well insulated with new windows and almost no leaks from outside.
When sizing is done without heat loss calculations, one must consider
1. House size
2. Type of house ..Detached, semi or townhome ( how many walls are exposed )
3. Insulation
4 Window size and conditions
5. Exposure to sunlight
fieldhousehandyman wrote: I have a 3000 square foot (on first and second floor) double brick Victorian home, uninsulated and installed an 85k BTU furnace which has no issue at all keeping the place heated.

I did the design calculation myself from a technical sheet posted on the CMHC website (no longer available) Actual design requirements were 57K BTU if I recall, I can send you the link to my blog which has the actual calculation.

40k btu is more than sufficient for your house, and is likely the smallest available furnace anyway.
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Deal Addict
Jan 19, 2011
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Here is the link to my calculation on my blog

Furnace Sizing Calculation

With this calculator, all you need to do a proper furnace size calculation is a few months of your winter gas bills, and some data from Environment Canada
"The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end; there it is."
Just a guy who dabbles in lots of stuff learning along the way. I do have opinions, and readily share them!
Jr. Member
Sep 21, 2015
126 posts
30 upvotes
Toronto, ON
As mentioned in previous poosts, there are many variables that affect the heatloss calcualtion. You can try the following, if ytou are interested https://hvaccomputer.com/index.asp.

For comparison, I recently did calcualtion on 1300sqft bungalow, with finished basement (~3' above ground basement walls).
This is for block wall basement, double brick wall constrcution, no wall insuallation, old windows, and R40 ceiling insulation.
Worst case scenario, would be 93,000 BTUH heat loss.
If I start adding insullation to walls, even as little as R5 (1" XPS), the heat loass get cut in more than half.
Deal Expert
Mar 23, 2009
18838 posts
4944 upvotes
Toronto
For my mediocrely insulated (portion of) my home that is two floors at about ~1900 sf plus an extra ~950 sf finished basement (so total over 2800 sf), the heat loss calculation came to ~63000 BTU according to a formal HVAC engineering assessment. Got a 70000 BTU (or 66000 BTU according to the manual) multi-stage variable-speed furnace installed and under normal conditions I have NEVER heard the fan ramp up beyond low, in almost a decade. In fact, usually I can't even hear the thing at all unless I'm in the basement near the furnace, or I'm very close to a register.

BTW, this 66000/70000 BTU furnace replaced a 100000 BTU furnace which was clearly oversized, presumably to compensate the for the poor duct layout. When we installed the new furnace, we adjusted the ducting somewhat, although it was mainly to get better cooling from our new AC unit.
Member
Oct 19, 2020
322 posts
189 upvotes
1cat2dogs wrote: Question for the experts:

Just got quoted for a 40000 BTUH Goodman 96% EFF 2 STG Gas furnace on a 1200 SF bungalow with 900 SF of finished basement.

That seems rather small to me? What says the experts?

1950s brick/brick with 20yr old windows and original insulation rental property.

TIA for any comments.
Are your walls brick veneer or block/double-brick?

The latter likely has zero insulation and it can't be economically upgraded.

The heat loss for insulated bungalows is disproportionately high relative to sq ft.

You may need as high as 60k btu, but it's better to get a smaller furnace if it will do the job.
Lennox/armstrong makes a 45k which is "safer".

Do your own basic calculation here: https://www.loadcalc.net/
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Mar 13, 2004
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We got a 40,000btu Goodman 2 stage furnace down from a 80,000btu installed by @newlyborn and its been great. Home is 1,200sq brick, semi no insulation home from around 1910.

40k seems about right for you in a bungalow. What current size & type of furnace do you have now?
1cat2dogs wrote: Question for the experts:

Just got quoted for a 40000 BTUH Goodman 96% EFF 2 STG Gas furnace on a 1200 SF bungalow with 900 SF of finished basement.

That seems rather small to me? What says the experts?

1950s brick/brick with 20yr old windows and original insulation rental property.

TIA for any comments.
0_o
<_<
>_>
Member
Oct 19, 2020
322 posts
189 upvotes
sickcars wrote: We got a 40,000btu Goodman 2 stage furnace down from a 80,000btu installed by @newlyborn and its been great. Home is 1,200sq brick, semi no insulation home from around 1910.

40k seems about right for you in a bungalow. What current size & type of furnace do you have now?
Just keep in mind that semis need less heat than detached and bungalows. Bungalows have the greatest heat loss per sq ft of any house type especially when a narrow rectangle.

40 may not cut it despite being a lower square footage.

If your house was a detached it would have needed something with at least 50k output, and since no one makes one it would have been a 60k input.
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Nov 28, 2016
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newlyborn wrote: I concur @fieldhousehandyman . We recently installed 60K in 3000 sq ft home AFTER homeowner got his heat loss calculations done. Even though house was 20+ years old, it was very well insulated with new windows and almost no leaks from outside.
When sizing is done without heat loss calculations, one must consider
1. House size
2. Type of house ..Detached, semi or townhome ( how many walls are exposed )
3. Insulation
4 Window size and conditions
5. Exposure to sunlight
Alot of this has to do with the Climate Zone you are in to I imagine

The BTU usage recommended for each house size is not a single number but rather a broad range. Square footage is not the only factor.

Climate zone
Edmonton is in Climate Zone 5. (Of course it’s the coldest.) Recommended BTUs are between 40 to 50 per square foot.
Quality of Insulation
How well is your home insulated? New homes tend to be around 50 BTUs and the older ones closer to 60 BTUs. To get the total BTUs required, you simply multiply the total square footage by the recommended BTU per square foot.
Other factors
Window thickness (single/double/triple glazed), ceiling height, number of people living in the home and the temperature they find comfortable.

The one you replaced was only using 20 BTU per sq. foot as the calculation. While I understand sq. footage is only one factor, the climate zone you live in has to be factored in as well doesnt it?

The same house in Ontario picked up and moved to Alberta or Saskatchewan, would not have the same size furnace. Or am I completly wrong on that?
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Jan 19, 2011
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WikkiWikki wrote: Alot of this has to do with the Climate Zone you are in to I imagine

The BTU usage recommended for each house size is not a single number but rather a broad range. Square footage is not the only factor.

Climate zone
Edmonton is in Climate Zone 5. (Of course it’s the coldest.) Recommended BTUs are between 40 to 50 per square foot.
Quality of Insulation
How well is your home insulated? New homes tend to be around 50 BTUs and the older ones closer to 60 BTUs. To get the total BTUs required, you simply multiply the total square footage by the recommended BTU per square foot.
Other factors
Window thickness (single/double/triple glazed), ceiling height, number of people living in the home and the temperature they find comfortable.

The one you replaced was only using 20 BTU per sq. foot as the calculation. While I understand sq. footage is only one factor, the climate zone you live in has to be factored in as well doesnt it?

The same house in Ontario picked up and moved to Alberta or Saskatchewan, would not have the same size furnace. Or am I completly wrong on that?
A furnace sizing calculation which uses actual fuel consumption, and local historical weather data, like in the page from my blog I linked, eliminates all conjecture, guesswork, and other factors that play a role in furnace sizing, rendering all that information moot.

The calculation uses actual consumption over three months, and three months of weather data, and does not care what size furnace you have, how many windows, how many floors, doors, how much square footage, or where the house happens to be located, as all that information is unnecessary
"The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end; there it is."
Just a guy who dabbles in lots of stuff learning along the way. I do have opinions, and readily share them!
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Nov 28, 2016
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fieldhousehandyman wrote: A furnace sizing calculation which uses actual fuel consumption, and local historical weather data, like in the page from my blog I linked, eliminates all conjecture, guesswork, and other factors that play a role in furnace sizing, rendering all that information moot.

The calculation uses actual consumption over three months, and three months of weather data, and does not care what size furnace you have, how many windows, how many floors, doors, how much square footage, or where the house happens to be located, as all that information is unnecessary
Im going to be diving into that tomorrow, Way better than the heat load calculation websites some post. You literally need to know everything about the house you live in for building materials to even get a something thats useful

Only issue with my calculation is having a NG furnace in my garage, so Im not sure how true the numbers will be
Deal Expert
Mar 23, 2009
18838 posts
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Toronto
WikkiWikki wrote: Alot of this has to do with the Climate Zone you are in to I imagine

The BTU usage recommended for each house size is not a single number but rather a broad range. Square footage is not the only factor.

Climate zone
Edmonton is in Climate Zone 5. (Of course it’s the coldest.) Recommended BTUs are between 40 to 50 per square foot.
Quality of Insulation
How well is your home insulated? New homes tend to be around 50 BTUs and the older ones closer to 60 BTUs. To get the total BTUs required, you simply multiply the total square footage by the recommended BTU per square foot.
Other factors
Window thickness (single/double/triple glazed), ceiling height, number of people living in the home and the temperature they find comfortable.

The one you replaced was only using 20 BTU per sq. foot as the calculation. While I understand sq. footage is only one factor, the climate zone you live in has to be factored in as well doesnt it?

The same house in Ontario picked up and moved to Alberta or Saskatchewan, would not have the same size furnace. Or am I completly wrong on that?
No. That is terrible advice.

That 50-60 BTU per sf rule of thumb would oversize the furnace the vast majority of time, unless you live in a very leaky and very poorly insulated century home or something.

In fact, even for zone 5, for a modern home with decent insulation and proper duct work, that rule of thumb would often oversize the furnace by 100-200%.
Last edited by EugW on Feb 22nd, 2021 7:11 am, edited 1 time in total.
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fieldhousehandyman wrote: Here is the link to my calculation on my blog

Furnace Sizing Calculation
Fieldhousehandyman's Blog wrote:A Sample Aggregate Count Of The Number Of People With Nothing Better To Do!
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Aah! I've been rickrolled into visiting your website!
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Quentin5 wrote: Aah! I've been rickrolled into visiting your website!
Lol gotcha... sadly I do not have a video of "Never Gonna give you up" anywhere on my blog
"The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end; there it is."
Just a guy who dabbles in lots of stuff learning along the way. I do have opinions, and readily share them!
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EugW wrote: No. That is terrible advice.

That 50-60 BTU per sf rule of thumb would oversize the furnace the vast majority of time, unless you live in a very leaky and very poorly insulated century home or something.

In fact, even for zone 5, for a modern home with decent insulation and proper duct work, that rule of thumb would often oversize the furnace by 100-200%.
But this is the problem. Every site has contradicting information. I looked at info for a few hours and last night. Some were as low as 20 Btu per sq foot all the way up to 60. All of these were HVAC sites as well. Canadian sites and US sites

Even on RFD there is contradicting info on sizing. And even with in person HVAC techs.

So the question is, who is actually right?
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WikkiWikki wrote: But this is the problem. Every site has contradicting information. I looked at info for a few hours and last night. Some were as low as 20 Btu per sq foot all the way up to 60. All of these were HVAC sites as well. Canadian sites and US sites

Even on RFD there is contradicting info on sizing. And even with in person HVAC techs.

So the question is, who is actually right?
All are wrong. A rule of thumb is oversized in order to work for most case scenarios which makes it wrong for most case scenarios except the worst end of it.
The correct way to size is either a calculation using past data (i have not checked fieldhousehandyman's method but i will assume he got it from or derived it correctly) or an energy audit which costs a few hundred dollars but is done with a site visit, measurements, computer software and a blower door test.

Every house is unique, its design, its components, its location, any upgrades done and how well it was built (hence the blower door), age, etc.
In fact in Rand McNally they wear hats on their feet and hamburders eat people
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Jan 19, 2011
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WikkiWikki wrote: But this is the problem. Every site has contradicting information. I looked at info for a few hours and last night. Some were as low as 20 Btu per sq foot all the way up to 60. All of these were HVAC sites as well. Canadian sites and US sites

Even on RFD there is contradicting info on sizing. And even with in person HVAC techs.

So the question is, who is actually right?
None of them are right, it is nothing more than guesswork... The only thing that works well is a furnace sizing calculator that uses two sets of data, actual energy consumption for the home you are sizing for, and local weather information (degree days)

stop wasting your time about who is right or wrong, an equation that uses ONLY fuel consumption and degree day data makes all of that other garbage completely irrelevant
"The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end; there it is."
Just a guy who dabbles in lots of stuff learning along the way. I do have opinions, and readily share them!
Deal Expert
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Nov 28, 2016
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Out west
fieldhousehandyman wrote: None of them are right, it is nothing more than guesswork... The only thing that works well is a furnace sizing calculator that uses two sets of data, actual energy consumption for the home you are sizing for, and local weather information (degree days)

stop wasting your time about who is right or wrong, an equation that uses ONLY fuel consumption and degree day data makes all of that other garbage completely irrelevant
I wish I found your info/blog a couple months ago, Ive been running around in circles trying to make the correct choice on a furnace replacement

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