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Re: Backdraft - Negative Air Pressure
rzxspz wrote:

The fireplace is a masonry chimney and is totally separate from the hot water heater. It only vents the fireplace. The house has a separate metal vent that the origional furnace and the hot water heater shared. The furnace has been replace with a high efficiency furnace, so now only the hot water heater is venting through the metal vent stack.

The house is two story with basement and the fireplace is in the basement.

Your fireplace still needs its own air intake.

Re: Backdraft - Negative Air Pressure
rzxspz wrote:

We experience cold air flowing down the masonry chimney when the fireplace is not in use - even when the damper is closed. When I do lite a fire, the fire tends to die down after 45 minutes or so and the fire seems to cause the hot water tank to backkdraft. How do I correct this? Would installing a 4" outside air intake to the return air on the furnace fix the problem? (I have a 90% efficiency furnace

Has this always been the case or is this something that just started hapening ? Has anything been done or changed within the home ?

In many jurisdictions the mechanical codes require a fresh air supply from outside to inside for combustion equipment. Usually a minimum 6 inch duct is required to bring in enough make up fresh air into the space for fuel fired furnaces , boilers , water heaters are located. Generally this was implemented for those appliances that were not direct vented and relied on the air within the home for combustion and vented out common type of flue.

Depending on your local requirement that 6 inch duct can simply dump cold air into the space ( about a foot off the floor ) -- or --- they can drop into a 5 gallon bucket --- or --- they can be tied into the cold air return plenum at a furnace.

In your case it sounds as though you have a direct vented ( intake combustion and exhaust ) so the requirment for the make up air duct for the furnace isn't required --- but --- you have a fuel fired water heater and a fireplace that are having back drafting issues.

I recommend getting a professional HVAC or chimney/fireplace spe******t or even an energy auditor to determine what the cause is for the negative pressure issue.
There are a myriad of things that can cause this issue --- from wind pressure --- partially insulated and sealed parts in the home --- flue issues --- etc

Re: Backdraft - Negative Air Pressure
HoustonRemodeler wrote:

Your fireplace still needs its own air intake.

Our Fireplace works fine and draws air from the house, I haven't seen a fireplace that draws it's own outside air. Like I said, I'm open to new ideas


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