Gas Furnace Not As Hot As Last Winter


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Old 01-04-14, 07:27 PM
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Gas Furnace Not As Hot As Last Winter

This is a 15-year-old 125,000 BTU(80% efficient) natural gas furnace. I think the manufacturer is GMC. The house is a older, drafty house, but it seemed to work OK last winter. Now it runs much of the time keeping the house at about 66-67F when the outside temps are 35F or down to 20F. The gas bill for December was much higher than it normally is. Feeling the outputs at the vents, it seems like the air isn't as hot as it was last winter.

Two different HVAC service techs looked at the furnace as it was operating but couldn't find anything really wrong with it. One of them cleaned the burners with compressed nitrogen to get a better flame color, but that didn't increase the heat output significantly. They also replaced the thermostat.

At this point I'm not sure what might be the problem. Any ideas?
 
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Old 01-04-14, 07:52 PM
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Start spending some time and money sealing up those air leaks.
Adding insulation in the attic.
Air sealing the attic, basement or crawl space.
Installing replacement windows.
Air sealing the rim joist.
All these items save money not cost money if you plan on staying there.
 
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Old 01-04-14, 09:04 PM
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Any chance of a squirrel having eaten a hole into a duct in the attic? If your gas bill has gone up, and your room temps have gone down, you are losing heat somewhere. It is bound to be in the most difficult spot to check.
 
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Old 01-05-14, 03:45 AM
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You mention two companies looked at the furnace and neither found a problem. Did either company inspect your ductwork? Like bentlerf mentioned you could have a hole or holes in your ductwork or a run or two may have come unhooked, dumping your heated air into the attic or crawl space.
 
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Old 01-05-14, 06:24 AM
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bentlerf, the duct work only runs under the floors using the crawl space, not into the attic.

Pilot Dane, nope they didn't inspect the duct work. If there was a hole or an unhooked run would the vents be outputting less air?
 
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Old 01-05-14, 10:24 AM
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"the duct work only runs under the floors using the crawl space, not into the attic.

if there was a hole it might heat up the area of the floor around the hole as air leaked out depending on how things are insulated. So you might be able to localize the problem by feeling the floor for heat. Any heat or foggy moist air coming out of the crawl space. Any moisture in the crawl space.
 
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Old 01-06-14, 04:08 PM
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Here's an update. Another HVAC guy looked at the system. The temps coming out of the furnace were extremely good. I think he said 130F. The problem seems to be with the ducts being in bad shape. Insulation falling off and sections that were becoming detached. The duct system will need to be redone.
 
 

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