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Old 02-15-2021, 01:15 PM
 
Location: Raleigh, NC
263 posts, read 472,615 times
Reputation: 206

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My house is a 1997 built 2 story vinyl siding w/ a 2 car unheated garage. Basic Goodman gas furnace single stage one zone which heats both up and downstairs. It is 40,000 at 80% so output of 32,000.

Question is everything I'm reading seems to indicate this is undersized based on my 1800 sq ft house with average insulation. Seems the minimum is 25 to 30 btu per sq ft which puts it at 48000 to 54000 btus needed.

We have changed the back door and 6 of 14 windows to newer more efficient. The first winter I was here there were days with temperature of 30 or so for the high and the heat could not get our house above 64 degrees. With the back door and windows replaced, we can achieve 68 now but I doubt much higher than that. We do have a gas fireplace as well which we use- I am not sure its output but I wonder if back when they put the furnace in they added the BTU output of the fireplace too- although that seems very odd.

The prior owner put in the unit around 2013, it works so I don't feel a need to change it until it breaks- but curious if my thoughs are right. The central air is a 3 ton which seems sized adequately- runs fine and can get down to 74 or below easily without being on all day like the furnace.
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Old 02-15-2021, 01:51 PM
 
Location: Raleigh
10,623 posts, read 8,053,926 times
Reputation: 15065
Quote:
Originally Posted by ippi76 View Post
My house is a 1997 built 2 story vinyl siding w/ a 2 car unheated garage. Basic Goodman gas furnace single stage one zone which heats both up and downstairs. It is 40,000 at 80% so output of 32,000.

Question is everything I'm reading seems to indicate this is undersized based on my 1800 sq ft house with average insulation. Seems the minimum is 25 to 30 btu per sq ft which puts it at 48000 to 54000 btus needed.

We have changed the back door and 6 of 14 windows to newer more efficient. The first winter I was here there were days with temperature of 30 or so for the high and the heat could not get our house above 64 degrees. With the back door and windows replaced, we can achieve 68 now but I doubt much higher than that. We do have a gas fireplace as well which we use- I am not sure its output but I wonder if back when they put the furnace in they added the BTU output of the fireplace too- although that seems very odd.

The prior owner put in the unit around 2013, it works so I don't feel a need to change it until it breaks- but curious if my thoughs are right. The central air is a 3 ton which seems sized adequately- runs fine and can get down to 74 or below easily without being on all day like the furnace.
Your experience (that you can't heat the house above 68) indicates that you are most likely correct, in the absence of an obvious answer that is being overlooked (like vents being closed or long neglected filters.)

I wonder if the previous owner had a fire place insert and supplemented heating that way.
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Old 02-15-2021, 02:29 PM
 
Location: Cary, NC
37,095 posts, read 64,465,722 times
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Is your gas fireplace a direct vent, or is it gas logs in a woodburning firebox?

If it is gas logs, your flue is, or must be, clamped open to prevent CO backing into the house.
That is one heck of a hole in the wall, creates an enormous draft even when the fireplace is not running.
I threw out the gas logs, removed the clamp on the firebox damper and the house was more comfortable.

It won't solve your problem, but if your flue damper is clamped open all year around, it is an energy hog.
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Old 02-15-2021, 03:19 PM
 
Location: Raleigh, NC
263 posts, read 472,615 times
Reputation: 206
Thanks! We do change the filters every 3 to 6 months (know it's 3 but sometimes forget). Interesting- it is direct vent so yes you're right Mike, there is cold air definitely by the fireplace! Wouldn't have thought of it- depending on how long we stay in this house good suggestion to ditch the fireplace and look into maybe a bigger furnace- or maybe by closing and replacing the rest of the downstairs windows we wouldn't even have to.

Jonov- could be right, maybe the prior was supplementing the heat with the fireplace or kind of only using the furnace for upstairs heat- who knows.
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Old 02-15-2021, 03:22 PM
 
Location: Raleigh
10,623 posts, read 8,053,926 times
Reputation: 15065
Quote:
Originally Posted by MikeJaquish View Post
Is your gas fireplace a direct vent, or is it gas logs in a woodburning firebox?

If it is gas logs, your flue is, or must be, clamped open to prevent CO backing into the house.
That is one heck of a hole in the wall, creates an enormous draft even when the fireplace is not running.
I threw out the gas logs, removed the clamp on the firebox damper and the house was more comfortable.

It won't solve your problem, but if your flue damper is clamped open all year around, it is an energy hog.
Is that local or new? My parents bought the house we grew up in in the early 90's. Gas logs in a firebox. Flu had to be opened before we'd turn on the fireplace. It was in the upper Midwest, but all the same the energy suck is the same. I think most of the neighbors had the same setup. It's just the first I've ever heard of it.
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Old 02-15-2021, 03:32 PM
 
Location: Cary, NC
37,095 posts, read 64,465,722 times
Reputation: 37170
Quote:
Originally Posted by JONOV View Post
Is that local or new? My parents bought the house we grew up in in the early 90's. Gas logs in a firebox. Flu had to be opened before we'd turn on the fireplace. It was in the upper Midwest, but all the same the energy suck is the same. I think most of the neighbors had the same setup. It's just the first I've ever heard of it.
My house was built in 1993, and the damper was clamped open for the gas logs when we bought it. But, I don't know the history.

Maybe Sherifftruman can offer some input.
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Old 02-15-2021, 04:21 PM
 
Location: Gaston County, N.C.
176 posts, read 79,796 times
Reputation: 220
Roughly speaking, it sounds undersized.

I have a few rentals with about 1200 SqFt of heated living area. The last time one of the furnaces needed replacement, I asked if 70,000 BTU (the 1960s spec) was oversized and if I should reduce. The HVAC guy said I plausibly could, but the next step down was somewhere around 45,000 BTU, in which case the house would only heat to the high 60s on very cold days.

I stuck with 70,000 since it was a rental, and figured I'd rather not hear any complaints from tenants during a rare arctic event. But if I was living there, I might have reduced the capacity as an experiment. If necessary, it's not that big a deal to plug in an electric space heater once in a while for whatever room I'd be in.
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Old Yesterday, 06:08 AM
 
Location: Morrisville, NC
8,421 posts, read 12,190,602 times
Reputation: 7830
So, the standards requiring damper stops for converted fireplaces came into effect in the early 1990s. And that would apply to any type of fireplace that could be for wood or gas and has a close able damper essentially. Loots of the pre fab units that people make for wood are also designed for gas, and some of them were changed to gas right from the beginning.

In practical terms, if you always open the damper before you turn the fire on and have a nearby CO detector? Well, adults are allowed to make their own decisions on lots of things where risk is involved. It’s a less than $10 part available at home improvement and hardware stores and takes 10 minutes to install in most fireplaces. But when you sell your house, if the buyers get the house inspected, a home inspector like me will have to mention it is missing regardless.

And even in order homes, it will get mentioned. A home inspection isn’t really a code inspection, at least to the level of finding out what exact codes were adopted and in effect at the time a home was built. If it is a danger in some way, almost all inspectors will bring it up as there was almost certainly a safety reason why it was implemented in the first place that likely exists regardless.
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Old Yesterday, 10:04 AM
 
Location: Raleigh NC
20,973 posts, read 11,055,437 times
Reputation: 12532
assuming that you get it serviced routinely (annually), and trust the service person, then personally I'd just ask them to tell me. A trustworthy HVAC person isn't going to tell you to replace a well-functioning system to pad his bank account.
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Old Today, 11:13 AM
 
Location: Raleigh, NC
263 posts, read 472,615 times
Reputation: 206
Great point BoBromhal- funny enough on the last tuneup I asked the tech if it was undersized and he said no it should be 60,000 and it is. I went up and triple checked after and sure enough it is 40,000- so off the cuff he assumed it was 60,000 gives me more credence it's under.

Another development is power went out for a little bit yesterday- nice to know the gas fireplace has a standing pilot so can work and so does our water heater- so god forbid a Texas situation, we'd at least have some heat and hot water assuming no gas outage.
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