co rise 1 ppm every 5 minutes

EJ hoffman

Just did a combustion analysis on a newer FAF 80+ fan assisted draft.  Room CO was at zero then slowly rose 1 ppm every five minutes. Flue gas Co started at 17 ppm and rose about 8 ppm every five minutes.  I had a Certified Proctor from a certified national testing group with me and he told me it was with in specs as it was below 35ppm in the room.  I told the homeowner she needed service and had a major problem to deal with, Yes after twenty minutes the room CO was at 4 ppm, but what happens when that FAF runs 24 7 to keep the house warm on a cold spell? What say the rest of you?

Mark Eatherton

I say...

NO CO is a good CO level, and if there is a leak from whatever source, it is not going to get better. It's going to get worse.



Things like this require one to exercise good judgement. Technically, the tech is correct. It is well below alarm limits. But if it is climbing, even slowly, things will only get worse, because as the appliance begins drawing the CO into the combustion process, the generation of CO will increase significantly due to the incoming combustion air being fouled with CO and CO2.



Bottom line, there IS a CO leak, and it needs to be found and eliminated. FAF are notorious for failing at the heat exchangers within 5 years of being turned on.



There is gent named Ellis Prach who has a book out detailing just about every force error heat exchanger ever built, and where to look to find the crack.



http://www.heatexchangerexperts.com/manual.htm



Pardon the pun, but his book is deadly accurate.



ME

Jean-David Beyer

Some seem worse than others.

My Quaker Meeting house was built almost 200 years ago. It had no heat. Later, it acquired three pot-bellied stoves. Later an oil burner. When I first went there, they had two gas burning forced hot air furnaces.They were installed by an incompetent contractor. I imagine the burners were the cheapest money could buy. They had 5 horizontal tubes with slots in them. Air was forced into the combustion area buy a blower. The combustion products went through the heat exchanger which was two sheets of bulging sheet steel, and up to the chimney. The burners were plain steel, and needed to be wire-brushed at the start of every heating system as the slots tended to rust closed. At some point, I suspected the heat exchangers were leaking as the flames began flickering in a way I was not used to. We got a more competent contractor who verified that the heat exchangers were, in fact, leaking. Just when I wondered about pulling the burner tubes out and having them nickel plated to stop the rusting. But I could not be sure to get all the pickling solution out of those tubes, so they would rust from the inside. Oh. Well.



The new gas burners are much better in this respect. Instead of having the heat exchanger running at positive pressure, so leaks would guarantee combustion products going into the building, the new heat exchanger is a two-stage one where fire is shot into the bottom tubes (large diameter), they then go to a manifold into three times as many smaller tubes, to a second manifold where a blower exhausts the combustion products to the chimney. These tubes are all of greater wall thickness than the old stamped steel sheet heat exchanger. By running the heat exchanger at a slight vacuum, leaks are much less likely to go into the building. And I have these units checked every year, which was not the custom before.

Tim McElwain

First ofd all the

"Certified Proctor" is incorrect. The 35 PPM is for a work site not a residence, EPA says no higher than 9 PPM in an eight hour time weighted average.



The Fan Assisted Furnace has as its only purpose for the fan is to overcome the internal resistance of the heat exchanger and insure that air for combustion from the space is maintained. It also does not require a sealed flue pipe. That being said there are plenty of places for CO to get into the ambient air. Rising CO is very definitely a problem. The maximum by the way for in the flue is 100 PPM (air free).



What combustion readings did you have for this unit especially interested in the draft reading?

EJ hoffman

after 5 minutes co in flue was 57

Yes was aware of the 9ppm I have never felt any co was good or acceptable I told the homeowner she had a problem that was serious and needed to call a service tech in to attend to the problem. Specifically ask if the techs used combustion analyzers an co detectors personally

Mark Eatherton

You did the right thing Ed...

Can't be overly safe in these situations.



ME