"Now my house is too tight"
Column #826 12/18/2010
On The Level
Q. We have a 1965 Rancher style home. Last August, I had an EPA Energy Star home audit. They closed a utility room ceiling air intake vent, added insulation over the utility room, installed a vent in the utility door and sealed the ducts. In early October, my carbon monoxide detector went off. Neither the fire department, water heater or furnace representatives could find the problem. In November I had a follow up audit done. They advised the house was too tight. I was advised I would need to have an electrician install a ceiling intake fan somewhere in the house to equalize the air. In the meantime, I am to keep a window partially open.
Some of the things done were positive. However what is accomplished if contractors are required to meet EPA standards only to have other contractors add fixtures that use electricity to meet healthful air quality? These audits are being done in a number of homes. I question how many of these homes are going to end up with unhealthy air quality without the owners knowing it? Shouldn’t the audits be done only during cold months when the furnaces are in use? What other alternatives are recommended?
A. Welcome to the world of unanticipated consequences. Even though the folks who responded to your calls when your carbon monoxide detector sounded the alarm may not have been able to pinpoint the exact source I can tell you for certain there are only two carbon monoxide sources in your house: the furnace and the water heater. Both are gas and both appear to be struggling for combustion air because the normal products of burning natural gas are carbon DIOXIDE and water vapor. That’s why on really cold mornings and days you see what looks like steam rising from the rooftop gas flues.
The primary method of buttoning up a dwelling to conserve the heat or cool inside is insulate, seal and caulk which is what was done at your house. Unfortunately, many of the folks who do such things have their eyes on the prize of measurable house tightness and have blinders on as to how a given house works. This has been going on for a long time beginning in the mid-1970s after the first Arab Oil Embargo shot fuel prices skyward and folks scrambled to not go broke heating their homes. And the laws of unanticipated consequences set in then too and the learning curve was begun to recognize such things. But as you’ve learned, not completely.
The second contractor was on the right track when he recognized the need to “ equalize” the air from inside the building to the outside. That’s certainly a part of it. But quite simply, your fuel burning devices, the furnace and water heater, are starving for air. And the cause is when the first contractor sealed up the ceiling vent in your utility room which was put there for the sole purpose of supplying combustion air from the unconditioned attic space which has vents at either end of the house to the outside. Plug that up and tighten the house as a whole with respects to air-infiltration and the poor devices are trying to suck air from a place that really doesn’t want to yield much air. Then the device tries to vent the burned fuel products to the outside which now has a higher relative air pressure than the inside and the flues gasses can’t make it all the way out of the building, causing your CO detector to go off.
You are both smart to have had a CO detector and lucky that it went off. The results could have been quite different. It’s even wiser to have two but in your case one did the trick. It doesn’t take much CO to cause problems. Your CO detector will sound at 70 ppm (parts per million of air) after a couple of hours of exposure. At 200 ppm most jurisdictions want the building evacuated and 500 to 1,000 ppm you can expect to die if you don’t get out before you lose consciousness. Contrast that with the fact that the oxygen we breathe in normal air comes to us naturally at a level of around 200,000 ppm and you can see just how nasty carbon monoxide is.
You don’t have to evaluate a home in the cold months to do an audit or to properly tighten a home. All you need to do is use the best diagnostic tools available and use them. I’m talking about one’s eyes and brains. You look around the house and catalog what’s there. If you see aspects of the home that won’t tolerate being sealed up in a tight environment you take measures to accommodate it, whatever it is. In your case I would reopen the ceiling vent and make sure they didn’t insulate over where it was-- I’m sure they did. After tightening the house, the vent they put in the utility room door went from useless to stupid. Then you won’t need a fan to bring unconditioned air into your uber-tight house. Keep the ceiling vent open and the door to the utility room closed and I’ll bet your CO levels will slide down to normal.
Overly tight buildings yield a product called “sick building syndrome” where the air is recirculated in a closed loop system and the only fresh air that gets into the place is when someone walks in from outside through an open door. But as door doesn’t stay open long. People inside for long periods begin to present all sorts of symptoms that can only be laid to the stale air.
There is a device that I really like that can take a building tight as submarine and keep the air fresh without breaking the fuel bank. It’s generically called an air to air heat exchanger. You can get a residential one for under $500. and they go by other names. They’re called Energy Recovery Ventilators (ERV) or Heat Recovery Ventilators (HRV) too. They’re fresh air exchange appliances that take fresh air into a dwelling, clean and evenly circulate it then expel stale, polluted air while controlling humidity and minimizing heat loss/gain. It’s not just houses with potential CO problems that can benefit from them. Any overly tight building regardless of the heating or cooling source would benefit from one. It’ll take a while but the house tightening armies will eventually get it-- it’s only been 35 years since we started down this road.
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