Slowpoke Furnace?

January 25, 2012 8:06 AM

Is my natural gas furnace acting normal or do I need to call out the repair guys?

I had a new natural gas furnace (Trane, I think it's a 95% efficiency) installed in 2008. When I'm at work I keep my house at 62 and have it between 66-68 when I'm home (p.s. I'm in the Seattle area).

When it's time for it to go from 62 to 66, it will pause for a few minutes after the temp goes up 2 degrees. Meaning once it hits 64, it'll stop for 3-4 minutes.

Is that normal? I don't recall any furnace I've lived with before doing that. Also, in my 1100 Sq.Ft. well-insulated (for a 1940s built) house, it can sometimes take over an hour for it to raise the temp a mere 4 degrees on a mild winter day--that can't be normal, can it?

It is matched with a heat pump, but when I'm home I usually switch it to the gas furnace because it's warmer heat and I'm a cold weather wimp.

Thanks gang!

posted by Zoyashka to Home & Garden (6 answers total)

I believe that's your thermostat: Modern thermostats are starting to play with all sorts of heuristics to account for the fact that heat may spread through your house in ways that could cause keeping the furnace on until the thermostat sensor reaches the temperature you've set could cause the house to overshoot that temperature.

Kind of like cooking meat, where the instructions often include a set of "bake in an X degree oven until the center of the meat gets to Y, then pull it out and put it in a foil tent and in 10 minutes the center will get to your desired temperature Z".

Same thing on the house: If your vent is in a different room, the furnace could raise that room to 75°, then the air for that will diffuse out in to the house 'til your thermostat senses it and says "oh, it's 68° now".

If this bugs you, check your thermostat manual, there are probably ways to turn off this sort of predictive behavior, or to tweak it.
posted by straw at 8:12 AM on January 25, 2012

No - I don't think its normal. 1 hour to raise 4 degrees seems strange to me. I live in a 1200 sq ft house and it takes less than 20 min to raise the temp 4 degrees. How long has this been going on? Since it is 2008, I would start with the thermostat as stated above. If that doesn't solve it, have someone come out and do a check and clean, meaning they do some diagnosis and clean out the burners and such. This should be under $100. Is your furnace filter clean?
posted by amazingstill at 9:02 AM on January 25, 2012

Your house may be well-insulated, but is it also well-sealed? They are very different things, and the latter can cause a significant loss of conditioned air.
posted by JohnFredra at 9:58 AM on January 25, 2012

Over an hour for 4F is not right, unless your furnace is way undersized (which would be quite difficult to achieve in a small house with a relatively new furnace in Seattle). A 3-4 minute pause doesn't really matter in the context of an hour.

The cause of this problem could be any number of things and if you don't feel comfortable troubleshooting yourself, you will need to call someone in (whoever installed the furnace is probably a good call).

One thing to check would be to make sure that the gas furnace is actually working during that hour. That time scale would make more sense if it were only the heat pump functioning.
posted by ssg at 10:13 AM on January 25, 2012

Check to make sure the return air duct isn't allowing outside (attic or crawlspace) air into the circuit. If it is, the furnace is struggling to heat new cold air rather than the warming, and recycling, inside air.
posted by bz at 10:20 AM on January 25, 2012

I would make sure that any ducts (intake or out) have no holes in them. It could be possible the heated air is escaping to the attic or basement.

My new 80 percent efficient furnace never pauses.It will step down to the 1st stage but never pauses. It takes like 10 min or less to heat my 850sf condo so 1 hour for 1200 feet sounds rather high to me.

Also do you have a heat pump also? Some areas that do not get decently cold (like under 50 f) have heat pumps with backup heat units.
posted by majortom1981 at 3:54 PM on January 25, 2012