My Boiler's Low Draft Readings

D107

My four year old Peerless MI-03 has about 3-4 mysterious ‘blocked-vent switch' (spill switch) lockouts a year, usually on the hottest, most humid summer days. When it happens I just hit the reset switch and it runs fine. I have two CO detectors right there—one a low-level monitor––with never any CO reading.

I’ve never gotten a draft reading printout—techs have measured it but then forgotten to write it down. They always said the reading was low; one preferred to test with the boiler room door closed, not sure why. There is no FAI in the room, but we never had one with our prior way oversized 210mbh firing WeilMClain, so figured this 70mbh would not require a fan-in-a-can or equivalent.

Our chimney, originally unlined for the prior boiler measures 7x10 and is 33 feet high. For this boiler a 5” liner was installed. Techs have speculated that low draft or the activation of the spill switch is caused by a nearby large tree and wind currents from the nearby river. The last tech showed me smoke rising into the flue during firing as if that was a legit draft test. I wondered if the lining was somehow botched; there’s really now way any squirrels got in there as the top cap and damper are closed off with wire mesh. Large setbacks? I looked up all the printouts I have from past combustion testing:





I did find draft readouts at different times from the prior large boiler of –.02" and –04"...

So I decided to pick up a Bacharach Draft-Rite, and got the following results. I conducted a breech reading 6” over the Field Controls Gas Vent Damper GVD-5.(Not barometric) with outside temps of 50º and 55ºF. I got repeated readings of –.02" to a trace above at steady state—boiler running about 8 minutes. Opening a window in the boiler room changed nothing. The reading without any combustion was still just slightly less than –.02". Stack temp was 210ºF but since prior stack temps showed 400º I suspect my Westwood T-42 gauge is inaccurate. I was not able to get a draft over fire reading since the observation port is so near to the flames I didn’t want to put the probe in there.

Once I get some opinions from The Wall, I will find a tech that does real full combustion test printouts and also have the chimney checked out. You will see in the photos that there is some kind of spring or something at the base of the chimney that I cannot identify.

On the other hand if –.02" is acceptable, and there's no combustion CO spillage, I can leave well enough alone, though the lockouts seems to suggest this shouldn't be acceptable.

captainco

-.02" draft is usually pretty decent when the temperature outside is above 40 degrees. High humidity or rain does lower it. Field Controls makes a Star Kap that is wind proof if that is the problem, but I think something else might be happening. If your alarms aren't going off at least it doesn't sound like severe problem. Unfortunately not to many techs have a clue how to diagnose these types of issues