How Much Outside Air Can Leak Into A House

Chad Bailey

Hello you guys. I am a Water Damage Restoration Contractor and I have built a trailer mounted Desiccant Refrigerant dehumidifier. I am doing some research on how much on average will a air conditioner leak air. Or will pull outside air from negative pressure or loose air from positive pressure. I have had a problem with getting small refrigerant dehumidifiers to work and I think this is the reason why. I belive that there is to much infiltration from outside and a 900Watt dehumidifier will not keep up.

I am just looking for answers. Ed the roofer told me about this site and said that you guys would be able to help.

mdshunk

Anywhere from a lot to a little. Google "Magnehelic Test" and "Blower Door Test", and look at any links to the department of energy in particular. This will give you a good starting place for average infiltration and exfiltration. My gut tells me that there's no way on this earth 900 watts will dehumidify a house. In terms of tonnage, that's only a little over a ton (750 watts per ton, approx). I'd think you'd want a dehumidification capacity equal to or exceeding the same value of comfort cooling capacity the home would otherwise need as a good rule of thumb.

Chad Bailey

Thanke you mdshunk

I have not been able to get people in the restoration industry to really talk with me about this. All I hear these guys with a whole ware house full of portable dehumidifiers say how well they work. I can not see them working that well though. They depend on the home hvac to cool them down. I think that hvac units leaks too much and they need to work without ac units. I can figure how much grains per pound in the air in a place from the ac. Usually around 60 in the summer and then the grains from outside. Then calculate the infiltration rates that I have heard(somewhere around 20% of the air that the ac unit is circulating) and the amount of water that comes in per day alone is more than a little dehumidifier can keep up with. Not to mention the water that comes from a water leak.

indoorwxexpert

Without a blower door test on each house you are shooting in the dark. I've seen some fairly new homes leak like a screen door. The more canned lights the worst the leakage is on newer homes. Older homes seem to have more leakage around the doors and windows. Most of your negative pressure on a house comes from ventilation fans (bath, clothes dryer) and outdoor wind conditions. A windy day causes much more infiltration than a calm day.

Anyway, good luck and take a building science class or two.

Ed the Roofer

Welcome to the forum Chad.

Off Topic, for a moment:

Guys, I received some very useful advice from this man via a post I made on a damage restoration forum due to a 2nd story unit leak into the 1st story unit. He went out of his way to even call me at my office last night to follow up with the situation.

Thank you and I hope you get the answers you are looking for.

Ed

Chad Bailey

Thanks Ed Sorry I have not posted back yet.

Thanks you guys. I have found two building science classes that I am going to take. I live in South Carolina and the company in north carolina said that they did air flow test on 200 houses and found a average of 15 go 20% of a homes air flow to leak. That means if your handler is circulating 2000 CFM of air then you will have about 400 CFM of infiltration.

If you take 400 CFM with 150 gpp outside conditiones thats 110 gallons of water a day. That would be 4.5 gallons a hour. Since Air conditioners do not remove all the water you could expect one to pull about 2.5 gallons per hour and that would leave you with about 60 GPP Inside of a house. Now if you take a couple of dehumidifiers and add some fans then you have alot of heat. Then the AC unit is running constantly and also the heat is high. Which makes the unit not be able to remove as much moisture. The dehumidifier also does not work under high temperatures since it cools air to the dew point. That means you have systems that are fighting each other and you still have all the humidity fighting in from outside. This is why I dont think refrigerand dehumidifers dont work well. I am just looking for proof. If I have been mumbling and you need me to clear something up I will be glad to.

Thanks
Chad Bailey