Are you sure you have a negative pressure problem.
What did your installing contractor install, that you think is causing the negative pressure.

 

What is the cause of negative pressure?

More air going out of a space than coming in.


What should my installing contractor do to fix this problem?


Depends what is causing the problem!

Thanks
Craig Aiugustine

More info definitely required!

 

negative pressure issue



When furnance is running outside air is being pulled in through cracks,around windows in basement. On first floor it pulls outside air through any space that is not totatly sealed. (I used to have a gravity feed furnance, I miss it) I have a older house with 2 cold air returns that use joist covered with nice reflective looking cardboard. One return uses 2 joist width and the other just 1. They are located on outside walls 1 by front door and 1 by rear door. What other info do you need 45000 btu 2 stage blower high effiency goodman

Thanks for any help
Craig A

 

Your question is to vague. Give specific particulars. Negative pressure by itself is just pressure. The application of pressure, negative and positive, and their relationship to proper operation will determine if they are a problem or not.

 

What makes you think, you have negative pressure!

I do need more information, but usaully we are changing pressures from slightly negative to slightly positive with high efficiency equipment. The way we correct that is with HRV/ERV (heat/energy recovery ventilator) and balance with pressure differential manometer.(fluke922) You can tell when you open door slightly if the building is positive or negative. If it closes you have positive or if it opens you have a negative pressure.(the door does have to be able to swing freely and not sticky). Beenthere is agood person to get in on this

 

confusing!!

Hi Craig
As a new member, like you, I get to throw my 2 cents in and can be forgiven for answering a question, or asking a question and being slightly off the mark.
The old guys on this form, and I don't necessarily mean age (I'm 62), will give us some latitude.

Your question has no answer.

Reason being:

You need to identify what causes you concern about the "negative pressure" and how you arrived at the fact you have it.

You need to identify what the contractor put in, and into what type of enclosure.

Describing return air ducts helps with nothing as it is only re-regurgitated air in a confined space.

Biggest cause of negative air is air depletion. Air depletion is caused from you and your wife breathing and combustion. Because of this you will need "extra air" brought into the house. Do you have this? If you don't, your cheeks will go from looking like a puffer fish, to that of your grandmothers with her teeth out.

 

sounds like the furnace draws in too much return air from the basement, either deliberately from a grille down there drawing in too much air or unitintentionally through all the leaks where the floor joists are lined or "panned"

Try leaving the basement door slightly ajar and watch what happens when the furnace kicks on

 

Is your high efficiency furnace vented with 2 pipes going to outdoors or just one? For best operation it should have it's combustion air piped directly from outside and not using inside air for combustion. Also do you have any exhaust fans in the house? (Bathroom fans, range hoods, clothes dryers?) All these pull air out of your house and that air needs to be replaced somehow.

 

"Negative building pressure results when an HVAC system inside a building draws in more air from the return ducts than it expels through the supply ducts. A building can be wholly under negative pressure, or exhibit zones of negative pressure in certain areas (e.g. a room contains a return air grille and no supply grille). Given the current configuration of most HVAC systems, most buildings operate under some degree of negative pressure.

When buildings operate under negative pressure, some air must be introduced from outside to balance the pressure differential. Ideally, this air would enter the HVAC unit through a valve or duct and be dehumidified before being introduced to the indoor environment. Unfortunately, however, this is rarely the case. HVAC units often have no allowance for outside air, meaning the air must be brought in from different areas. This often results in air being sucked in around doors and windows, through cracks in the foundation, or through other penetrations in the building skin. When this occurs, the introduced air is not dehumidified before entering the indoor environment. Over time, the indoor relative humidity will increase, potentially causing mold growth on cool interior surfaces or inside wall cavities. In addition, negative building pressure can introduce soil gases into the home, including radon.

To eliminate negative building pressure, the HVAC system must be reconfigured so that any outside air that comes into the home passes over the condenser coils. This process requires careful calculation and precision, so it should only be attempted by a professional."

 

"Negative building pressure results when an HVAC system inside a building draws in more air from the return ducts than it expels through the supply ducts. A building can be wholly under negative pressure, or exhibit zones of negative pressure in certain areas (e.g. a room contains a return air grille and no supply grille). Given the current configuration of most HVAC systems, most buildings operate under some degree of negative pressure.

Only one fact missing pertaining to the sentence quoted above: "Negative building pressure results when an HVAC system inside a building draws in more air from the return ducts than it expels through the supply ducts". EDIT: Return leaks...if the return ducting is outside the conditioned space, such as an attic or crawl space, return leaks will positively pressurize certain areas of the home. This positive pressure is in respect to outdoors. The end result is the same; infiltration is accelerated in the area under a negative pressure, and the area under positive pressure may be pushing air through wall cavities and penetrations into the ceiling. Under certain conditions that could lead to condensation within the walls (if indoor humidity levels are high enough), and possible mold growth (in addition to compromising insulation R value).

Supply leaks outside the conditioned space can cause one or more interior spaces to go negative.

When buildings operate under negative pressure, some air must be introduced from outside to balance the pressure differential. Ideally, this air would enter the HVAC unit through a valve or duct and be dehumidified before being introduced to the indoor environment. Unfortunately, however, this is rarely the case. HVAC units often have no allowance for outside air, meaning the air must be brought in from different areas. This often results in air being sucked in around doors and windows, through cracks in the foundation, or through other penetrations in the building skin. When this occurs, the introduced air is not dehumidified before entering the indoor environment. Over time, the indoor relative humidity will increase, potentially causing mold growth on cool interior surfaces or inside wall cavities. In addition, negative building pressure can introduce soil gases into the home, including radon.

The dehumidification need is true for cooling season...in heating season the same scenario outlined above can result in low indoor air humidity levels.

To eliminate negative building pressure, the HVAC system must be reconfigured so that any outside air that comes into the home passes over the condenser coils. This process requires careful calculation and precision, so it should only be attempted by a professional."

The word "condenser" is an error. It should read "evaporator".

Another approach to reducing/eliminating negative building pressure is to seal the entire supply and return duct system, like it always should be. Outside air can then be brought in, if the house has tighter construction than normal, to keep indoor air fresh. It will, as noted above, need to be humidified or dehumidified as warranted by season.

 

My house sucks too.

It would help if you let us know how the house is recieiving outside air (aside from the leaks).

 

Good chance. You always had those leaks.
Just with an old gravity. You never noticed it. Because gravity systems provided a more consistent heat, as it got colder outside.

Now with the forced air. Its causing more stack effect.

Its also possible, that if you have stack heads for the supplies in the wall cavities. That they are leaking air into the wall, and out teh attic, causing the negative pressure.

 

It seems to me that there is probably a supply leak outside the building envelope, like the attic since it happens only when the furnace runs. It might be worse now with the new furnace because it may move more air, therefore leaking more air outside.