CO Poisoning

[bb]

Alert: If you are in the DFW area keep an eye out for improperly converted furnace closets. I had a call a couple of weeks ago where the homeowners were exposed to CO gases all night. When I arrived 4 hours after the furnace had been turned off, my CO detector read 98 ppm within 4 minutes. The homeowners had allowed Oncor to send out contractors (homeowner couldn't remember what company) to convert the furnace closet. IE seal the closet. Well they sealed it alright but forgot to cut in combustion air vents into the attic. The homeowners said it looked like a couple of kids that came out and did the job. They were lucky to have awakened that morning. It took 40 minutes with all of the doors open to clear the house down to 0 ppm. I wonder how many more are out there like that. BTW Oncor hung up on the homeowner twice and told her that that program has ended and they didn't keep any records of who did the job, which has to be BS. I refered them to the Dept of Licensing and Regulation and the city.

[gravity]

cutting holes into the attic will 99% of the time not bring fresh air for combustion. 99% of the time it will act as a path for exhaust. next time take some tissue paper and hold it up to the so called fresh air intake and tell me which way the tissue moves.

[SBKold]

How would this immediately cause spill?

[gravity]

I think you have another problem going on. Or you created another path for the furnace to vent by cutting chases that lead to the attic.


Here's a good read about combustion air
http://ncidavid.blogspot.com/2012/08...ombustion.html

[Kobe RBVBD]

I saw this same thing today, actually. I can't say the company name for legal reasons, but they sealed the entire furnace closet. What I'm saying is they put sheetrock compound over the lower and upper combustion, weather stripped the door, put gasket on the bottom of the door. The furnace was completely sealed in, no air was going in or out. Scary stuff. I was sent out because the furnace was short cycling afterward. No duh.

[beenthere]

cutting holes into the attic will 99% of the time not bring fresh air for combustion. 99% of the time it will act as a path for exhaust. next time take some tissue paper and hold it up to the so called fresh air intake and tell me which way the tissue moves.

If the room is sealed, and its an induced draft furnace, the vent to the attic will pull air into the room/closet.

The tissue test will give a false impression if the door is open while you hold it up to the vent.

[gravity]

Good point beenthere. I knew this but didn't explain it well. Are these heaters induced or natural?

[hearthman]

You can test the MUA hole from the attic with the door sealed. Sadly, combustion analysis on such a setup is useless because the numbers can drastically change once the door closes. Need a Plexiglass door with those full length rubber gloves like in The Andromeda Strain. TiCl4 smoke puffer is MUCH more accurate than tissue and can tell direction of airflow either way. Tissue is subject to gravity (pun intended Tom).

[bb]

Good point beenthere. I knew this but didn't explain it well. Are these heaters induced or natural?

What diffference would it make? Any 80% induced or natural draft both need combustion air. We don't use many 90 % furnace down here in the great state of Texas.

[Jim Davis]

When a furnace is in a small closet you have to put your probe in the flue and run your analzyer hose outside the closet and close the door the best you can. In a case like this where initially flue temperature is not important, you can take any piece of plastic tubing and a piece of copper and make your own probe that can reach outside the closet.

If combustion air pipes coming from attics to mechanical rooms can cause 80% furnaces to spill, then the whole ceiling open will be worse. I have seen this many times. I have also tested in Texas and so far, all attics were sucking out of the room. A simple 4 X 10 supply registier on the plenum is all that is needed in that room and close up the attic!

[beenthere]

What diffference would it make? Any 80% induced or natural draft both need combustion air. We don't use many 90 % furnace down here in the great state of Texas.

If the closet is sealed from the occupied space, then the opening to the attic can't draft air out. but when you have the door open, it will draft air into the attic. Some times people forget that when the room is sealed(door closed and it is sealed) the attic doesn't draft air out.

Of course, there are 1000s and 1000s of those closets that aren't sealed from the occupied space.

[Rich]

For new tradesmen and FYI:
Obtaining combustion air from an attic for an atmospheric furnace that is located in a closet the following rules apply.

National Fuel Gas Code 5.3.3

1. The attic MUST have ample ventilation.
2. A vent on the ceiling is required whose function is actually an OUTLET air vent
3. An inlet Air DUCT from the attic should extend to 1 foot above the finished floor.
Not mentioned in the code, but will cause problems if the duct system is not sealed in the closet area, especially on the return air side.

I would post a copy of the codes picture but I don't think its allowed on this link.

You can also use duct to extend outside the wall of the furnace, the same principal applies, one on the top and one on the bottom.

[chuckcrj]

For new tradesmen and FYI:
Obtaining combustion air from an attic for an atmospheric furnace that is located in a closet the following rules apply.

National Fuel Gas Code 5.3.3

1. The attic MUST have ample ventilation.
2. A vent on the ceiling is required whose function is actually an OUTLET air vent
3. An inlet Air DUCT from the attic should extend to 1 foot above the finished floor.
Not mentioned in the code, but will cause problems if the duct system is not sealed in the closet area, especially on the return air side.

I would post a copy of the codes picture but I don't think its allowed on this link.

You can also use duct to extend outside the wall of the furnace, the same principal applies, one on the top and one on the bottom.

I'm sure you know this Rich, but don't install combustion air according to code and walk away without testing. Make sure it is actually working. ASHRAE found that passive combustion air intakes don't always work. Fan powered combustion air is the best.