Re: Furnace sizing question
I'm trying to see if I read this correctly ..... you will have the foam installed behind the sloped ceiling ?
Originally Posted by Mary S
If so you will have approx. R24 upstairs in the ceiling but very low R value in the rest of the home ..... I highly doubt you'll see a 40% reduction in your heating bills .......it will help the comfort level upstairs.
Doubtful this would have any signifigant impact to warrant a reduction in furnace size.
There's no way anyone over the internet can say what size of furnace would be correct .... you need to have a Manual J heat load evaluation done .
The existing furnace is an 80,000 BTU single stage gas furnace and is 12 years old.
Will the added insulation make enough of a difference that a smaller furnace will be appropriate?
If so, how much smaller would be right for this size house? What is the consequence if one has a 'too large' furnace?
And how much too large does a furnace have to be to cause a problem or significant inefficiency? (I.e., is something like 20,000 extra BTU no big deal?) I am very lucky that I will actually have to pay only half the cost of the furnace and installation, so initial cost is less of an issue than it would normally be.
Chances are you may end up with the same sized unit if it was sized correctly .... depends on the load calculation.
Going to a larger size serves no purpose ... in fact has negative impacts. A larger unit will heat the space too quickly and short cycle often instead of running the optimum duration and frequency..... short cycling will wear the furnace out quicker.
A larger furnace will also put out a higher volume of air and likely your duct work wouldn't be correctly sized for this creating velocity noise.
This is true .... they are both 90% units .... the 2 stage has better control for comfort.
Also, one furnace guy told me that the choice between a 90% efficient single stage furnace or a 90% efficient 2 stage furnaces is mainly a comfort issue, not an issue of operating cost savings...Is that true?
"" an ounce of perception -- a pound of obscure "