cold air coming out of register


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Old 05-16-08, 11:30 AM
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Question cold air coming out of register

I have a Luxaire gas fired(propane) forced air system at my cabin in northern wi.It's a horizontal unit,model p-hdd12no6901b.I kept it at 48 degs during the winter.I know it was a cold winter but we were billed twice for fill ups recently which is unusual.When I went up there I noticed the air coming out of the vents was very cool.I checked the furnace and everything seemed to be working properly.The flame was there and there was plenty of air flow.I kept turning the heat higher and it would slowly rise.It wasn't until it got into the mid 60's that warm air started coming out.What gives?
 
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Old 05-16-08, 06:47 PM
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The important thing to know is the past history of this.

Is this unusual for this furnace to behave this way at 48 degrees inside? If not, could be simply a puny unit (low btu output) and the return air so dilutes the heat, it can only heat to any meaningful degree once the place is warmed up.

But obviously this would not apply if say you were to tell me that even at 48, it could put out 100 at the register.

You might want to take actual thermometer readings down in the register, rather than go by what you feel, as that can be very deceiving.
 
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Old 05-16-08, 07:38 PM
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cold air

You may also want to check the ducts to insure they are connected & undamaged. You could be pulling in cold outdoor air thru a damaged return. Most gas furnaces only increase the incoming air temperature by 50 to 60.
 
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Old 05-16-08, 07:55 PM
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cold air

I did look at the ductwork as well as I could.I didn't see any problems though most of it is covered in insulation.As for this being normal,I don't remember the air being cold like this in past years,but I don't think I made a point of checking it either.Could there be something wrong with the heat exchanger?Also,is the system just recycling the same air through the cold air returns back through the furnace. The unit puts out 75,000 btus into bout 1100 sq ft.
 
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Old 05-16-08, 08:07 PM
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Recycling

Yes, air is drawn in thru the returns, passes across the heat exchanger & is blown out thru the supplies. Any signs of soot on/in the furnace or vent system? I'm wondering if you are getting full capacity. Dirty burners will reduce the capacity & cause increased LP usage. Soot would be a dead give-away of something truely wrong.
 
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Old 05-16-08, 08:15 PM
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cold air

I remember there was a little blackness around the edge of the pvc vent,but the furnace seems to put out a nice blue flame.Am I missing something?
 
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Old 05-17-08, 05:00 PM
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Black

I suggest you get a pro to give the system a good going over. You should not see any black. Something is not right.
 
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Old 05-17-08, 07:20 PM
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cold air

I was hoping to avoid having someone look at it for cost reasons,but I guess I have no choice.Thanks for all the help.
 
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Old 05-18-08, 10:45 AM
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You never answered what the starting temperature was in the cabin when you had that problem with cool heat.

It really sounds like a typical "temperature rise" situation you got here, based on the fact in your OP you said register temp gets warmer as the cabin warms up.

If you ever need help and really want to save money, you need to answer the questions and not assume they might be irrelevant, or that some people just ask questions just to ask questions. Some people think of standing next to a fire burning when they think of heating, and can't figure out what the temperature in a house (at a register) has to do with what temperature it is in the house. They think that fire is hundreds or into low thousands of degrees and should put that out of the register at 40 below zero inside or 65 inside. It won't. See Grady's numbers below.

Oh. And 90- 110 degree air, when blown out forcefully, actually feels cool. That is why I wished you used a thermometer.

My inefficient furnace puts out 180 degrees (works up to that before shutting off) at the register (oversized furnace for the place) and neighbor kids love coming over and sitting on my registers (clothing/they don't get scorched as they know about that) when they feel cold.

Your furnace size sounds about in the right ballpark, if insulated cabin like a house.
 
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Old 05-18-08, 05:56 PM
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ecman51, what I meant was that the temperature was at 48 degs. in the cabin when I turned on the furnace.I had thought about using a thermometer,unfortunately I didn't have one handy.If Grady is correct and the temperature only rises 50-60 degs,that would make the temp. coming out of the register maybe 98 degs. minimum.I do know that the air coming out can feel much colder than it really is,but this air just felt too cold.I remember now that I placed my hand at the register just a few feet from the heat exchanger (its for heating the crawl space where the furnace is located)and It felt just as cold there. Over a period of time the temperature did rise in the cabin,but it didn't really start to feel warm (lukewarm actually) until the temp. got into the lower to mid sixties in the cabin.I'm basing all this on my gut feelings and experience over the years of feeling air coming out of registers.I do admit that I normally don't start with this low of ambient air temp.I will get a thermometer the next time I go up.
 
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Old 05-19-08, 11:20 AM
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Yes. Please do that with the thermometer, because otherwise what that will cause us to do here is maybe speculate on stuff for nothing.

We already know you have nice blue flame, yet not warm enough (at first).

Also be conscious of how well the air blows (volume/velocity) out the registers compared to the way you remember that it has in the past.

Also look to see how high the flames are off the burners. I haven't looked in a furnace quite lately, but you should see an inner, low, blue cone that is maybe 1/2 -3/4? inch high ontop the burner, and then a different color blue for the rest of the flame that should be several inches high, uniform across all burners from front to back.
 
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Old 05-19-08, 03:59 PM
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I don't think the velocity of the air has changed.It's blowing pretty strong,but I will take a closer look at the flames.It's hard to see through that little window.I'll probably just take the back panel off and look at the whole thing.It's just really hard to get to. Thanks for the suggestions.
 
 

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