new furnace sanity check
I've been reading a number of threads in this forum and found some of my answers and must say it is a wealth of information.... thanks already.
I am in the midst of buying a new furnace/AC - midst meaning I have made a deposit and waiting for installation.
Here is my question....
my current furnace -
Keeprite 65,000 BTU with rated output of 49,000 - I assume it is likely lower as it is 20+ years old. This baby has kept us fairly toasty through all that mother nature has thrown at us.
new furnace -
Carrier ICS (MVC) modulating furnace with infinity control. 60,000 btu with humidifier. I don't think they make them any smaller.
Our house is a mid-80's build - 1600 sq ft or so (excluding basement).
So the sanity check is - does that sound like I am sized right? (I know, I know - do the calc). Just want some feedback. My logic is that my crappy 20+ year old 60K btu furnace has been keeping us warm, so a new efficient one (3 stage), should do just fine....
spending lots of $$$ so just want a sanity check that this is not too small... sales guy was talking originally about an 80.
If a 65,000 80% was keeping youor house warm. then a 60,000 90% should have no problem.
Depending on where you're at, I'd say a 40,000 may do it.
Have a load calc done.
Most older furnaces are over-sized, and I see many customers with oversized units complain of high gas bills, and those with properly sized equipment not quite so disappointed when the gas bill shows up.
"Hey Lama, hey, how about a little something, you know, for the effort." And he says, "there won't be any money, but when you die, on your deathbed, you will receive total consciousness." So I got that goin' for me, which is nice. - Carl Spackler
HAVE A FINE, TOASTY, LESS EXPENSIVE TIME !
You've answered your own question! _FINE_ - 54,000 BTU output is adequate - more than 99%of the time - for 1,600 square feet for a 1980 vintage house.
Originally Posted by rpm2203
You will not have a problem unless the design temperature, say which might ~ 5'F, is significantly exceeded. If the temperature goes down to -10'F, your house might be ~8'F less than desired (something like 66 'F Instead of 74'F: 'fairly toasty') for a few (hopefully) hours. Such an event is Extremely Remote!
IF YOU ARE STILL Worried, an HVAC person is not the person you need to see.
In any such situation, you're going to provide your own form of Auxiliary Heat anyway if the "minor" (yes, debatable) inside temperature decrease is deemed unacceptable.
Aux Heat - for SIGNIFICANTLY LESS than Design temperature.
2. QUALITY 1,500 W (~5,000 BTU) Electric Heater
_______ REST V E R Y WELL. ! !!
Last edited by dan sw fl; 11-09-2009 at 09:40 PM.
It's Not Rocket Science, But It is SCIENCE
with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE
Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities
Thanks for the considered reply Designer Dan.
I live in southern ontario by (somewhat) the lake, so doesn't usually get that cold... Our old inefficient 65000 BTU furnace has been doing well for the past years keeping us warm with seemingly little problem.
My furnace salesman was pushing this 80K unit at me saying that it might be oversized, but the variable settings would cover that. - no comments please -. It seemed to me that even at the lowest btu setting, I wasn't too far from where my current furnace was assuming a drop in efficiency from the rated 75%.
I pushed back at them and they agreed that the 60K unit would do the job. It seemed that I would be getting 150% of what I already had 45K btu (of old) to 76K btu of an 80K unit. That seemed way overkill.... Still I hate pushing back on something I have relatively little knowledge of.