OK right sized (smaller) is better, but...

[Piedmont user]

I've got a 95,000 BTU/hr unit with a 82% efficiency (77.9 output kBTU/hr). I've been recording duty cycles and show that design temperature (23ºF) my duty cycle is only 35% (77.9 * .35 = 27.3 kBTU/hr). Even at record temperature (-10ºF) my duty cycle would be only 66% (77.9 * .66 = 51.4 kBTU/hr).

I have only about 1/3 of the sealing, 1/2 the duct sealing and 1/2 of the insulation done, so if I go a little small, I can still make up the difference with more work and/or an electric space heater during record hours. Assuming I can easily cut 10% with additional work, then my requirement drops to 24.6 kBTU/hr for a design temperature (23ºF).

Enough setup, now the questions:

If I have an appropriate furnace installed (45 kBTU/hr input, one of the smallest ones) what will a future home inspector say when I go to sell? Will my house get a "black mark" as a home with an under-sized furnace since my new furnace will be half the size of my current furnace?

[jimj]

I have never known of an inspector to do a manual J. I wish they would I would be down sizing a lot of systems.

[mike_home]

In my experience home inspectors don't note the size of the furnace in your inspection report. Even if the the inspector did this, how would know the current furnance is half the size of the old furnance?

You will score points on the inspection report by having a 95% efficiency furnace and one that is newer. If the buyer did have a concern about it being too small, then you could show a Manual J calcualtion showing it is correctly sized. You could also show your duty cycle readings at various temperatures as further proof.

[MLC HVAC MVP]

If record all of the data you just stated I don't see a problem. Now once you install this smaller unit and your data is not correct, you will get black marked from the Inspector.

[tedkidd]

Sounds like a 3 ton 2 stage hp with 5kw electric backup would be perfect.