Furnace blows cold air at 68, heat at 72

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Old 04-03-13, 09:31 AM
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Furnace blows cold air at 68, heat at 72

We keep our gas furnace at 68 during the winter and in the past month I finally realized that it blows and blows but never gets warm--until I put it up to 72. Then it gets warm quickly--too warm for me and I have to put the heat back down.

Here's the info I found: the thermostat says Trane "Weatherton"--showed the temperature at 65 although it's set at 69. Outside unit is Trane XB10 (but is that the a/c unit? I don't know, sorry). Upstairs in attic is Trane XB80.

After shivering for an hour with the non-stop blowing of cold air, I finally put the heat up to 72 and it's now blowing hot air--and more quietly, too.
 

Last edited by Bham45; 04-03-13 at 10:12 AM. Reason: Additional info
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Old 04-03-13, 12:09 PM
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By cold, do you mean room temperature?

Has it always done this?

Can you post the thermostat model number?

Have any changes been made recently?

Does the outdoor unit come on when you turn the heat on?

I suspect that t-stat may have been setup for a heatpump with electric backup, based on your description.
 
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Old 04-03-13, 12:26 PM
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Yes, I guess it must be room temperature air--not A/C air. It just feels cold to me because it's blowing down on me when I'm at the computer.

It's always been the case that it blows cold first and then heat finally comes along, but in the past month or so I realized that it was NEVER getting hot, and was blowing constantly. When switched up to 72, the air becomes warm and then it stops blowing for a time.

Here's what I got off the thermostat: BAYSTAT240A 3AAT82B1B2

No changes have been made at all.

When I was outside getting the model number for the unit, it was silent. I came in and the heat was on (but this was after I had put it up to 72). Want me to check if it comes on when it's at 68?

I do know that neighbors have talked about heat pumps: at our annual meetings someone brought up the fact that when he walks his dog at night he hears people's heat pumps on when they don't need to be. My husband and I looked at each other blankly because we don't know a thing about that. We don't think it happens to us but are not positive.
 
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Old 04-03-13, 02:50 PM
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Does the t-stat have an aux heat light on it? (see: http://dar.proflo.com/darmanager/Que...E=INSTALLATION)

When you switch on the heat, does the fan come on right away or is there a delay?

What's the full model number of the outdoor unit?

According to the model number, your t-stat appears to be for a heatpump (which is a "reversible" a/c so it can heat and cool, not just cool) -> not a gas furnace and central a/c.

If you can, remove the t-stat from the base and post a picture of the wiring.
 
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Old 04-03-13, 04:00 PM
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Here are some pics that show the Aux heat light and the wiring. That light went on when I touched the wiring and tilted it up slightly. It's not usually on.

Went outside in the rain to get this model number: 2TWB0042A1000AB. The fan was spinning as I was out there.

I think there's a slight pause before the heat goes on. If we change it at all, like pushing it up from 68 to 72 degrees, it shuts off for a minute or so before it starts back up.
 
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Old 04-03-13, 04:40 PM
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You have a dual fuel system. First stage is heat pump and second stage (aux) is gas heat. In alabama you should be mostly running on HP. It is possible that there is a problem with the heat pump and it may need serviced.
 
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Old 04-03-13, 05:09 PM
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I had called a company that does plumbing plus heat and a/c to have someone come out--but then when I turned it up to 72 and got hot air, I told them to forget it. But I did say I'd sign up for their twice yearly heat/air maintenance program. She asked which I'd like to start with and I said a/c. Do I switch to starting with the heat--or leave that as is and consider this heat pump a separate issue?
 
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Old 04-03-13, 05:26 PM
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Yup - you have a heatpump /w furnace for backup, so the t-stat type is correct.

There's most likely another control beside the furnace (or in the hp) which shuts down the heatpump and turns on the furnace below a certain outdoor temperature. (or when the temperature is far below the setting - ie when aux heat light comes on)

Recommendations:

1. Measure the difference between the supply and return air temperature when the heatpump is running. (heat on without aux heat light on)

It should be 18F-30F+ unless there's a problem or it's really cold outside. (well below freezing)

If the air isn't even warm, get the heatpump checked out - something is wrong.

Heatpump heat is far less intense than furnace heat -> it should feel luke warm; don't expect it to feel hot.

2. Switch the t-stat to emergency heat for now if there's a problem with the heatpump. Emergency heat disables the heatpump so all the heat gets supplied by the furnace.

3. Decide whether you want to use the heatpump for heat in the long run. If not, run it in emergency heat mode all the time; otherwise...

Those older t-stats wait for the indoor temperature to drop a bit before turning on the backup heat (furnace in your case).

If you'd like to use the heatpump for heat, replace the t-stat with an electronic one which doesn't have that issue.

Do a search on this board for "dual fuel heatpump" -> there's a wealth of information here.
 
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Old 04-03-13, 08:24 PM
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Thanks for all the info, but I'm afraid I understand very little of it. Especially step #1--have no idea how I would do that.

You aren't saying, are you, that an electronic thermostat would solve these issues? Or do we need a new heat pump?

I'll look up "dual fuel heatpump" tomorrow and try to get myself educated on the subject. Or I'll just give up and call a professional.

Just FYI: my husband switched the thermostat to AUX heat and we finally got some warmth.
 
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Old 04-04-13, 06:59 PM
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...your best option is to leave the t-stat in emergency heat mode - it will work like a normal system - furnace provides heat, a/c provides cooling.

The use of the heatpump for heating is optional; if you don't like it, there's no need to use it.
 
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Old 04-06-13, 10:07 AM
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Thanks for your help, Muggle and hvactech. Now that our temps are headed for the 70s and 80s this week, the hvac company is coming out on Wed. to do the a/c tune-up--and I told them to please check the heat pump while they're at it. I'll let you know what they tell me.

Maybe I'll have them put in a new thermostat--any suggestions?
 
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Old 04-06-13, 06:33 PM
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The heatpump IS the a/c too.

There's no need for a new t-stat if you choose to use the furnace exclusively for heat.

Ignore my previous advice since it's over your head. (no offense intended)
 
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Old 04-07-13, 09:10 PM
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No offense taken--it IS over my head.

But if we continue to use the heat pump, do you think we need a new thermostat?

There definitely is something wrong with the heat pump: when my husband turns on the Aux heat (furnace) it gets hot really fast. If left as usual, the fan will run forever but it's just cool air blowing around.
 
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Old 04-08-13, 12:42 PM
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With the heatpump on, the air shouldn't be hot -> it should be luke warm.

Body temperature is 98F, so moving air below that feels cool even though it's still warm

Heatpumps put out 85-100F air depending on the outdoor temperature -> the colder it is outside, the less heat they put out.

In comparison, furnaces put out 120F+ air.

Now, if the air is only room temperature, something is wrong.

When it gets too cold for the heatpump to heat the house properly, the furnace is supposed to take over automatically.

When the temperature in the house is significantly lower the t-stat setting, the t-stat turns on the furnace instead.

In many cases an outdoor thermostat is used as well to prevent the heatpump from even trying to heat the house below a certain temperature.

Newer electronic t-stats don't wait for it to drop to 68 when set to 72 to bring the furnace on (instead of heatpump)-> they're much better at sensing when the heatpump can no longer keep up than the old ones are.

But like I said before, you can just run it in emergency heat mode if you find it to be too drafty in heatpump mode.
 
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Old 04-08-13, 12:46 PM
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The purpose of having a heatpump is to reduce heating costs, mostly in mild weather -> they pump heat from the outdoor air inside rather than produce heat directly. (similar to your refrigerator -> remove heat from inside and dump it into the room)

This is a good introduction to the topic: What Is a Heat Pump and How Does It Work? | Office of Energy Efficiency
 
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Old 04-10-13, 12:26 PM
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Exclamation Does this sound legit? New condenser?

I was a little annoyed with you, Muggle, that you didn't seem to believe me that I knew things were different in regard to the lack of heat we were getting from the heat pump. Yes, I know it's not as hot as the furnace, but no warmth at all was coming from while it kept blowing and blowing. And then the temps went up to the high 70s/low 80s yesterday, and my husband could tell the a/c wasn't working as it should.

So a heating/ac guy came this morning and the good news is that I was right about the heat pump not putting out the amount of heat it ought to, but the really bad news is that we need a new condenser.

Okay, he said we could just pump more freon into it, but that would be a waste of money since there's a leak in the e-coil. He said it was so low, it was creating a vacuum in on itself--whatever that means. He was amazed we had heat as long as we have had it. We could replace the e-coil itself, but since it's an R-22, it will get more expensive to service as they are being phased out.

So then we had the option of various types of new condensers and we chose the Carrier Performance Series 15 HP w/coil. Please tell me that's a good choice.

Oh, and I brought up what you had said about only using the furnace and he admitted that that was an option but the dual-fuel will save us money in the long run. And most Southerners, when they go up north, get nosebleeds and dry sinuses because we're not used to this hotter, drier air that comes from furnace heat. I will attest to that myself: I actually miss the humidity we have down here when we travel--as far as my sinuses are concerned.

So we're a bit stunned at this sudden expense, but I guess our system has been hanging by a thread for a long time. I just hope we made the right decision.
 

Last edited by Bham45; 04-10-13 at 03:23 PM.
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Old 04-10-13, 06:16 PM
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Here's my husband's current thought: that we just get the coil replaced for about $2400. If we stay in the house and decide later to get the updated condensing unit, do you think it will cost less because we already paid for a new coil? We were quoted about $6100 for the Carrier I mentioned previously, but that included a new coil. Would the coil they put in now work for a new condensing unit in the future? Or would it be specific to this R-22 unit and need to be updated too?

We appreciate any help/advice you can offer!
 
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Old 04-12-13, 06:05 PM
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Bham45

I was a little annoyed with you, Muggle, that you didn't seem to believe me that I knew things were different in regard to the lack of heat we were getting from the heat pump.
Sorry for the misunderstanding.


-----------------------

$2400 for a coil replacement is really excessive - seek a second opinion. I know prices vary, but it shouldn't cost nearly that much.

Based on what's involved, I wouldn't pay more than $1500 for that kind of job.

$6k is also seems a bit high for a new heatpump and coil, but I'm not too familiar with heatpump pricing.

If the existing unit is less than 10 years old, get it fixed for sure.

He's right in that dual fuel is cheaper to run in a mild climate; that, and without fixing the heatpump, you won't have a/c.

--------------------------
Re: the dryness of heat...

People commonly think that furnaces dry out the air, when it's air leakage that's responsible for that.

Cold, outdoor air has very little moisture in it in absolute terms, and when it's heated, the absolute humidity stays the same but total amount of moisture that it can hold goes way up.

In some cases showering/cooking produces enough moisture to compensate for leakage; in others, there's so much air leakage that a humidifier is necessary.

But, heatpump heat shouldn't feel any dryer than furnace heat.
 
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