I had an estimate today from a local hvac company, and they figured
that a 60,000 btu furnace should replace my 105,000 btu furnace. it
is in a double family, brick constructed home that was built in 1949.
The furnace is working fine, I just thought i might get a replacement
estimate before it breaks down.
Does this sound reasonable? he took measurements of all the windows,
and walls, and got a reading for what walls/ceilings were insulated
and came up with this estimate. it does seem like he did a good job,
but i am wondering if i am being bamboozled, or if long ago they just
slammed too many btu's into housing units.
Thanks for the comments. Let me know if you need more information for
this to make sense.
Ask the guy if he'll replace it if it isn't big enough. If he says yes,
that's good enough. If he has a good reputation, he'll stand behind his
word. Remember, the next 6 contractors you get to look at it will tell you
to get a 105MBH heater because most consumers are scared of going lower.
I come up with numbers like that all the time, especially when new windows
and insulation was added since the old furnace was installed. With a smaller
furnace, your heat is going to be more even as long as there's enough CFM,
but newer blowers are usually more powerful. Consumers almost always think
"bigger is better". I just tell the people that if it isn't big enough, I'll
pull it out and put in a bigger one at no charge. Haven't had to do that
Very good point, yes he gave a 100% warranty/guarantee. If i dont
like it for any reason he said he would replace it or give the money
back. You are right about the cfm, but funny thing is the fan looks
just about identical to the fan i have in my primary residence, and
that furnace was installed in 1981.
You are lucky , it looks like you got someone honest that knows his
trade the first time, 99% of what I see here is no load calc questions.
I had 110000 btu and super insulated on 1800 sq ft in zone 5, to -15f,
and my last load calc was 50000 btu. Insulate to optimal, not just code
and you will require even less. With your smaller unit you will now heat
more evenly and short cycle less.
Well, part of it is that the BTU is input. If you are using a higher
efficiency unit (and I assume you are) the BTU capacity should be lower.
Should it be 1/3 lower? Probably not, but it is possible that the builder
just put the same unit in every house and yours was smaller than most.
Or maybe you insulated or improved the windows since 1949?
Since 1949 there probably had been added insulation, new windows, storm
doors, etc.; and new more efficient furnace designs. Yes, it was quite
common to go bigger as it was cheap back then. If your furnace cycles
frequently, that is a sign of over capacity.
Everyone here is wrong, dead wrong so far. Make sure you get a dual stage
furnace which measures 80% of the existing BTU output.
Most of the hvacs are crooks and will promiss the sun and stars and leave
you stranded. It is far better to overproportion the heater than under.
Conventional furnaces deliver a burst of cold rushing air when they turn on,
a dual stage applies even, consistant heat. The house will be warmer,
tennants content and the fuel bill will be far lower due to the absense of
A dual capacity unit is a good idea, but will still not compensate for
oversizing . Have the contractor do the job. It was not uncommon in
1949 to oversize by a factor of 2 or 3.
Fish, it sounds like you found a gem of a contractor. Don't let him
Slim Bastard is wrong, I never could get the house within 5 degrees in
several rooms with a 110000 btu unit , going to a 47000 low fire on a 2
stage got me temps to within 2 degrees. I atribute this to longer
running. Also Slimy, It is even heat, no hot blasts and less short
cycling. Short cycling doesnt allow rated efficiency to be realised
since warm up periods dont give full efficiency, it is also harder on
the equipment. This of course is for a furnace, Boilers are another
how long does the furnace you have now run on the coldest days to wamr
if it has to run only about 50% of the time on the coldest days then
you are probably ok getting a smaller one...
if your present furnace has to run 100% of the time on the coldest days
to keep the house warm, then a smaller unit may not deliver enough heat
on the coldest days...
just figure a furnace with 1/2 the output will run about twice as long
as your present unit...
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.