Negative pressure in my furnace room

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It wouldn't but again it would cause a overhot furnace, wouldn't do the blower wheel much good either
wrote:

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Look. If the furnace is pulling a vacuum in the room in which it is enclosed, obviously the air return for the blower is open to that room somehow (which it obviously should not be). I would not be surprised if there were a substantial opening in the cold air drop. I don't think small leaks in the ductwork would move enough air to produce the described effect (closing doors etc.)
The furnace in a house I own was installed by somebody who forgot to cut open a piece of tin between the main air return duct and a couple of branch return ducts. As a result there was almost no ductwork allocated to return air in the upstairs. When the furnace didn't work, somebody cut a hole in the cold air drop in the basement and put in a register. 90% of the return air for the furnace came thru this register, and it would slam the door at the top of the basement stairs. The people lived with this for 17 years before I bought the house and discovered the problem, and got out my tin snips.

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I would recommend an expert. Negative pressure and a gas furnace with water heater means CO poisoning and dead people.

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Could it be positive pressure in the house, since the garage door is not a remedy to the pressure problem? If not this is a serious hazard and should be looked at by a service tech. right away...
Joseph

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wrote:

The return duct is under negative pressure.There is a leak in the return duct. When you open the garage door, air is sucked into that leak, pulling the garage into negative pressure. Where does that extra air go? Into the house. Does this give you positive pressure in the house? Positively.
Gary
HVACR Trouble Shooting Books/Software http://www.techmethod.com
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If the return is open in the attic space or what ever, it could be only the house that is pressurized, no?
Joseph

not
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wrote:

Is the garage pressurized, too?
Gary
HVACR Trouble Shooting Books/Software http://www.techmethod.com
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The garage is not pressurized at all, that's the point. If the wet room had a negative pressure in it why wouldn't all three doors act exactly the same way? The impression I got from the op is that it is strong only on the door to the house.
Maybe I am missing something here, I guess I'd like to Know if any other exterior doors exhibit the same pressure effect?
Joseph

only
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wrote:

The impression I got from his first paragraph is that the furnace room is negative in relation to both the house and the garage.
Gary
HVACR Trouble Shooting Books/Software http://www.techmethod.com
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Gary R. Lloyd wrote:

Yes, that's right. I feel resistance when I open the door to the either the garage or the kitchen. (Both doors swing away from the furnace room. ) Even if I open the garage door first, there is still resistance when I open the kitchen door. This is surprising, because the two vehicle doors in the garage are not particularly well sealed to the outside world.
The safety issue someone raise because I blocked the combusion air openings for the dryer and water heater is a good point that I will fix, once this low-pressure problem is resolved.
Donald mentioned an opening somewhere in the return duct within the furnace room. So I looked closer. All the sheet metal is new, (less than three years, installed with the new furnace). All looks perfect. However, when I removed the humidistat for the Aprilaire 560, and looked at the junction between a horizontal duct at the ceiling and the vertical duct bringing the return air to the furnace, I could see light at the two rear corners. That's where the leaks are. The band that is supposed to surround the junction isn't properly installed. It will be tough to fix, as that junction is only two inches from the wall, and I can't get closer to it than 24 inches, because of the location of the water heater on one side and the furnace on the other. But I will figure something out.
Thanks to all for your replies. Never expected so many.
Ray
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Be certain that ther is actually not a return air grille in the furnace room. This will cause a negative pressure especially if there is no supply register to the same space. Another poster suggests to seal the return air plenum in the furnace room for the same reasons.
Kevin
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