Heat gain/loss report and Furnace sizing

[Jim418]

I received my Heat gain/loss report and it indicates a heating equipment load of 57,019. FYI I am in Kitchener Ontario.

If a furnace has 60K input and 95 AFUE, its output would be 57,000, right?
If a furnace has 66K input and 95 AFUE, its output would be 62,700, right?

Would either of these be sufficient? Is there any upside or downside to going to a larger furnace (additional cost is minimal)?

Thanks.

[BaldLoonie]

Usually that's the way it works out. But for those looking, when you get below an 80% furnace, output doesn't get lower!

I wouldn't worry about either for your application, whichever product & dealer you prefer.

[john_ertw]

A furnace sized exactly at your load requirement will be able to keep the house at the set temperature when the outside temperature is at the design temperature. If you lowered the temperature when you go to sleep and want it to heat the house back to your normal temperature when you wake up you will need some spare capacity. I would think a 70,000 or 80,000 btu furnace would be ideal for you, but let's see what the pros say.

[Jim418]

"It's acceptable for the output of unit to be up to 140% of the heat loss. You would still be in that range with a 80000 btu furnace."

For me, 140% of 57000 = 80,000. So I guess if I went up to a Lennox G61V-090 with output of 88K BTU that would be too big.

Sounds like the G61V-070 is the right size. Its first stage (which will be used the large majority of the time) will run at a much lower level than the 090.

[john_ertw]

I think the 70,000 btu unit sounds right. Do you know if the the consultant used CSA F280 to size calculate the heat loss/gain? I know it states going upto 140% of design conditions.

Do you mind sharing who the consultant was since I had lots of trouble finding anyone in the GTA to do heat gain/loss calcs?

Also for interest is this a new house you are building or did you have the calc done for the replacement of your existing furnace?

[Gunnery Sergeant Hartman]

Go with an 80,000 btu staged or modulating furnace! When the temps drop below design you will still be covered and wont be grossly oversized when the temps are just a little chilly.

[Jim418]

I think the 70,000 btu unit sounds right. Do you know if the the consultant used CSA F280 to size calculate the heat loss/gain? I know it states going upto 140% of design conditions.

Do you mind sharing who the consultant was since I had lots of trouble finding anyone in the GTA to do heat gain/loss calcs?

Also for interest is this a new house you are building or did you have the calc done for the replacement of your existing furnace?

I am doing a replacement furnace and AC. The report says "Printout certified by HRAI to meet all requirements of CAN/CSA-F280-M90"

The consultant's company is HVAC Delineation. Based out of Cambridge. Email is
hvacdelineation
AT
rogers
dot com

Charged me $ for an in-home evaluation. I believe she does drawing-based evaluations for around $. Uses Wrightsoft software.

[Jim418]

Go with an 80,000 btu staged or modulating furnace! When the temps drop below design you will still be covered and wont be grossly oversized when the temps are just a little chilly.

I'm planning on a 2-stage. I am only going to be in the home for 5 years so it doesn't make sense for me to shell out for a modulating furnace (but I will probably check the cost differential!)

[beenthere]

Many homes in Canada are built tighter then here in the USA.

But, if your house isnt built real tight. I'd see about improving infiltration, and lowering the heat need, and use the smallest furnace I could.

[Jim418]

Many homes in Canada are built tighter then here in the USA.

But, if your house isnt built real tight. I'd see about improving infiltration, and lowering the heat need, and use the smallest furnace I could.

Thanks. Just had an energy audit yesterday and when the guy ran the air leakage test he immediately said "wow, is your house ever tight!".

His only recommendation in terms of infiltration was weatherstripping around our cold-cellar door!

So I think I am good in that department and will go for a furnace on the smaller size.

Thanks.

[beenthere]

Compare his leakage rate, with teh rate that was used in the calc.
If the calc used a higher rate. Then you are safe with either of those furnaces you listed in your OP.

[Jim418]

Compare his leakage rate, with teh rate that was used in the calc.
If the calc used a higher rate. Then you are safe with either of those furnaces you listed in your OP.

In the Infiltration section, it used the "F280" method and the calc used a construction method of "Tight". This is consistent with the auditor's comments, but for the "F280" method is that as precise as it gets?

[beenthere]

Don't know. We don't use F280 here. Thats a Canada thing.