O/T any HVAC guys out here that can answer a question for me

[Dave]

Looking to replace the gas forced air furnace in the house here and Id like to get some answers on size  and btu ratings
TIA
Dave

[Sean]

I'm an HVAC guy, but all we do is commercial work. Everything is already figured out for us, we just go to the job and start installing stuff...

[GPster]

A place to start is with what you have. What are you heating with now and how old is it? A gas furnace that is more than 20 years old has probably dropped to 50% of it's BTU rating (which is the amount of gas it burns, not how much heat it gives) so a furnace that was 100,000 BTU is probably only giving you 50,000 BTU of heat. If that kept you warm than that's how much output you need from a new furnace that is 90% to 98% efficient. Residential cooling can be a guess from there because you're not dealing with a people load, lights or equipment. But the best rule of thumb might still be a contracter that is use to the area and can figure hours of light, humidity, wind and can look at the structure and it's exposure. GPster

[jaybee]

We had a new one put in several winters ago, they told us the one we had was probably sized about right since it was keeping up on the coldest nights & fit the "rule book" so they replaced it with another of same capacity.  We've been much more comfortable since, though, probably in part because the blower runs every so often even if the burner doesn't light in order to stir the air in the house.

This is a good time to take a hard look at your insulation as well and get it up to spec.  Recommended thickness of insulation has increased over time as fuel as gone up.  Don't forget the basement or crawl space.  Intuition says heat rises so it shouldn't be that important.  Reality is heat will leave the structure through any available path.