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The traditional way without using the accurate manual J format, was to allow 40 btu's per sq ft. In your case this would be 64,000 btu. Given your additional information I feel the 70,000 would be an accurate choice.
Of course though the best way is to have the load caluclation done which takes into account, insulation, windows, exposure, climate etc....
Depends on how you have duct available for future use...but yes....that scale you very close to the 70,000 btu, and if amply insulated the 70,000 will be sufficient.
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billy is the 90000 over doing the btu that are needed in michigan
Depends if it is 2 stage or variable. Now Michigan is a Hot/cold state. So if this was "loose construction" I would err towards a 90,000. But your home is fairly new....and well insulated, I would stick with 70,000. Furnaces have oversized for many many years...it is hard for us to scale down. In your situation 70,000 would be the choice I would offer.
I am from the the same state.....so I am taking climate into consideration.
Ok....that changes things....
A 2 stage is like having 2 furnaces....a small one when it is not that cold, and a big one when it really needs it.
Since this is 2 stage I withdraw my opinion and submit the 90,000. The 90,000 now becomes a "it is there if you need it"...but is not running 90,000 btu all the time.
The beauty here is the first stage will handle a good portion of the heating...especially early season and late.
Therefore, seeing how it is the given model...I change my mind. Sorry.
Given it is a 2 stage furnace means it will run at even less than 70,000 when a lot of heat is not needed. The 90,000 is like insurance.
The big thing here is it just like buying 2 furnaces....one for keeping up and standard temps...and another furnace just in case.
I amyself put in a 2 stage...I already had a single stage 90%...but the 2 stage saved me even more on my gas bill.
I still stick with 2 stage 90,000. If it were single stage I would not.
The sizing is so close around the 1600...plus if you add sq ft.
Look at it as buying a new car that runs on the highway on 4 cylinders....but if you need has 8 cylinders....
I agree with their statement.....IF it were single stage.
The humidity and mold would be products of the air conditioning.....but this G61 has multiple speed blower so it can be dialed in for proper ac operation.
I also looked ast the unit specs here http://www.cozyparts.com/Lennox-Parts/forum/Lennox_service_manual/Furnaces/G61MP_09-01-2007.pdf
Page 2 will tell you that low fire runs at 60,000.....and high fire is actually 88,000, they just round it up.
Most of the time it will run at 60,000 btu, not 70,000. and then when on high fire it is 88,000 btu.
There is really nothing I can do to make you feel comfortable in the decision. If you want to be certain, ask the contractors to supply a manual J sizing form.
This will take all information and mathmatically tell you what you need. Any quality contractor can/will be able to do this for you.
i respect your knowledge you have given some of the best answers not only that we will be heating the basement in the winter which is 800 square feet so if you feel the 2 stage 90 is the best i will do that
Given the basement sq ft makes an even stronger case for the G61 90,000.
I really do think you would be happy with it. The 2 stage is what makes all the difference.
Sorry for delay....
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