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Furnace vents question

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Why should there be cold air coming out of the cold air return and some out out of heat registers? Or am I just getting old and dumber? Here's the situation. We were at our lake home last Sunday--wind blowing really strong. Holding my hand down by the cold air return I could feel cold air coming out when the furnace wasn't running. Its a single story house, partial walkout basement. The furnace is down in the basement. Furnace is around a 2007 model, high effic. LP. It has the PVC pipe intake and exhaust. The guy who did the installing ran the pvc exhaust pipe up the chimmney instead of going out thru a wall.

Experimenting, I went down the basement, shut off furnace, disconnected exhaust pipe, plugged openings for intake and exhaust on the furnace. Holding my hand over pipe going up the chimney I could feel suction. Thought I had found problem. Went back upstairs, held my hand by cold air register, still air coming out. Also could feel air coming out heat registers.

Back down basement, pulled filter, cut piece of cardboard, put in place of filter, back upstairs, could still feel air, but not as much. Covered hot air registers, still feel air coming out.

The furnace seems to run an awful lot, if we were there in the winter I don't know if it would hardly shut off.

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My first question is why the $#@! did he run the exhaust piping UP the chimney? Not good! That tells me a bit about him...next question is, do you have/where is your fresh air intake located? I'm betting he ran it right into the ductwork on the intake side, and that is what you are feeling. Fresh air intake should terminate in an insulated drop box directly adjacent to the furnace. I'd check that stuff first.

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Air intake is right on top of furnace. He didn't run any pvc pipe outside. Don't know if he figured there was enough air leaking in around basement doors or what.

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Air intake is right on top of furnace. He didn't run any pvc pipe outside. Don't know if he figured there was enough air leaking in around basement doors or what.

So, you have no fresh air ductwork bringing in air from outside?

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Correct. Its sucking in basement air. In our furnace at home both intake and exhaust come out the side of the house.

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May I suggest you get a qualified HVAC tech over there pronto. No fresh air inlet is NOT proper, nor is it even anywhere near meeting code. You are putting yourself at great CO poisoning risk with this set-up.

I'll bow out of this one and hope you get this problem taken care of ASAP!

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Depending on the brand and model of furnace not all intakes need to be hooked up. We will still hook them up even though you do not have to. There is nothing wrong with putting the exhaust up the chimney. We have done many of them. Do you have a air exchanger? If you do the air could be coming from that and it is running all the time. If not look for the fresh air intake like RebelSS had said. on a windy day it could be blowing right in there into your furnace ducts.

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No air exchanger. What I cannot for the life of me understand is how when I disconnected and plugged air intake and exhaust outlet there was still air flow thru the duct work. Its a closed system. No air can get in.

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There likely are dampers in the duct work. Look for a metal piece that is in the middle of the bottom of a duct. It will be flat and about 3 inches long. The handle should be in the direction of air flow, parallel to the duct. If it is in the closed position it will be 90 degrees from the air flow direction. There's a chance that could be the problem. I don't like it as a solution but check it anyway. Otherwise I think getting someone out to check is a good idea. Of course the problem with that is getting someone out on a weekend when you're up there.

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You said it was real windy out .Maybe air leaks through out your house causes air to go into one room and push that air into both supply and return duct work to another room .....

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I'll take a look at the ducts and see if I see any dampers. Haven't noticed any before. Windows and doors are tight, the only place I can feel air moving is by the furnace vents. Was wondering if the duct work could set up its own ciculation between cold duct and hot duct, but my covering the heat registers should have stopped this.

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What year was the house built? It used to be very common to have a outdoor air intake (4" or 6" flex duct typically) piped directly to the return air duct. If the house is really old, you may just have that much infiltration. Return airs on inside or outside wall? outside used to be quite common, not much insulation behind the return there either.

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House was built in the 70's. Don't see any air intake from the outside. Cold air return on inside wall. When I held my hand down by the air return last Sunday it felt like there was a duct running straight to the outside but there isn't.

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Sorry, I'm at a loss of where it is coming from.... I'm assuming you can see all portions of your duckwork.. if not, maybe a fish camera could help you pin point the problem..

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l strongly suggest you have a qualified HVAC tech inspect that system, especially since you have no fresh air intake for a combustion device. Why screw around for answers when it may cost you dearly?

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being that you have a direct vent furnace you need significantly less outside combustion air if any at all, so I wouldn't worry about the fact there isn't outside air vent into your house. The 2 pvc lines are combustion intake and the other exhaust and your furnace has a sealed combustion chamber Co cannot get into the house unless you have a cracked heat exchanger

The cold air coming from vent could be just natural air circulation through the house similar to how a natural flow boiler works without a pump warm air rises cold air falls it may feel cool but its possible its actually warmer than the basement

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crix, yeah thats what I think has to be happening, its setting up its own circulation. I,m not heating the basement. There's a basement vent but I have it closed. Suppose I could try opening it for the heck of it. Maybe a cold basement has something to do with it. Heading up this weekend--have to see whats coming out the vents when everything is cold.

Have hi eff. furnace in home and can't feel any air coming out cold air vent.

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What your feeling coming out of the air return has to be getting pulled in from some where. Tell us more about the chimney.

How many devises are exhausted in the house?

Range hoods, bath fans, drier, water heater, chimney, and so forth.

If I were you, I'd hook up the combustion air intake to the furnace to the outside. Why, because! smile

IMO your house leaks an incredibly amount of air.

A home energy audit is what you should do but for now here is a DYI Home Energy Audit

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Opening around pvc pipe that goes into chimney is plugged. No other exhaust devices in the house. FWIW after furnace had run I went down in the basement, opened basement hot air vent and it would draw smoke in. Pulled furnace filter and it would draw smoke into that opening.

The heat ducts coming off furnace is a box maybe 10 or 12" by about 2 ft. wide probably 15' long going two directions. The 8" pipes come off the top of these and go to each room. Don't know if the large volume of air in the ducts would have any thing to do with it or not.

I know there's a good depth of insulation in the attic. Assume the walls are insulated.

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