Many things done but natural draft boiler still spills randomly.

chiefswabjockey

Long story, but this is our first fall/winter in this house and from the beginning I was having spill problems causing the boiler to shut down. I had someone out to look at it.

1) They told me we needed a fresh air intake to prevent negative pressure in the house. I reluctantly went ahead and had the 4 inch intake they recommended installed.

-- Flue kept spilling.

2) They sent someone else out who then inspected the chimney/liner etc. They told me that we needed to have a new chimney liner installed because the one was not sized right (too big) and was installed in a "squashed" manner. I had a new, properly sized, liner installed by a 3rd party.

-- Problem did not occur for over a week, but just discovered the boiler shut down and had to reset the spill sensor.

So now I have a big hole in the side of the house letting cold air into the basement mechanical room and a new liner but I am no further ahead.

The only thing that seemed to make everything work fine, or at least I had no problems while I had it this way while waiting for the new liner to get installed, was to force my automatic flue damper in always-open position.

Now, I hate this prospect I not only have a big hole to the outside letting cold air in but I also have a huge chimney constantly sucking the warm air out of the basement into the void.

I hope somebody out there is more knowledgeable than the folks who sent me down this path and can point at the smoking gun. Everybody has examined the damper itself and says it's fine ... and I tend to agree, as even after I reset the boiler the damper opened before the boiler fired and for a little while I definitely felt the hot exhaust coming down out of the flue until it eventually changed direction.

Help!

how

The Btu's of all gas appliances using this liner?
The diameter of furnace vent and liner?
The height of the chimney? Is it on an outside wall or enclosed within the house?
Why a 4 " fresh air and not a 5"???
A bit of initial spillage is fine provided that it completely reverses to draw the air around the boiler up the chimney.
The ameritherm dampers of the 80's & 90's allowed up to a minute of spillage.
I also wonder if the spillage sensor is poorly positioned or overly sensitive.

hvactech126

I also wonder about the position of the sensor. If it worked fine with the damper in the hold open position that tells us that it happens when the damper closes after a call for heat is completed.... Is the boiler a standing pilot? If so make sure that the small disc in the damper has been removed to allow for minimal flow while not calling for heat. Can you post some pictures?

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how

hey hvactech126
Good point on the pilot possibility.
Another possibility though would be that an always open vent damper would lead to a constant chimney draft powered by the escaping warmer house air. A boiler firing up into that established chimney draft might have significantly less starting spillage than a boiler having to initiate that draft.

yuri

did your techs check the manifold gas pressure to make sure it is not 2 high and overfired? probably has spark ignition and no pilot so it needs no hole in damper.

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chiefswabjockey

Hi Guys. Let me try to address some of the questions.

1- The only appliance venting up the liner is the boiler which is 100,000 btus.

2- The vent on the boiler is 6", which is now reduced to 5" into the 5" liner. Multiple people checked the books on this one and determined 5" was all that was needed.

3- I have no idea why they recommended 4 inch intake over something larger. The house is somewhat tight but it cannot be as tight as any new construction given it was built in the 1930s and is of a double brick wall construction etc. It has new windows/doors and an r50 insulated attic etc. but I'm sure there are tons of crevices in the house letting air in all of the time.

4- The boiler is only about 8 years old, it is a spark ignition so there is no standing pilot. There shouldn't be a hole in the damper blade but I'm going to check.

5- The chimney is about 30 feet high and is external to the house (the house is about 8 years old). It was previously a wood burning chimney. At some point in the past it was rebuilt so it is in good shape and it is a couple feet higher than the top of the roof (house is a 1.5 storey with a very pitched roof).

6 - As far as I know nobody has checked manifold gas pressure.

The other factors here are these:

- There ARE two louvered air vents in the wall leading to the living area from the boiler room though they aren't much bigger than standard heating registers. Actually, the chimney guy who did the liner told me to cover them with cardboard which I did but I am now questioning his logic.

- The ceiling of the boiler room is actually open to the rest of the basement ceiling since the finished ceiling is about 6 inches or so dropped due to presence of pot lights etc.

- The ceiling of the boiler room / basement is actually open directly to the main floor through some unterminated heating registers almost directly above the boiler room in the living room. I think these were put in to give the boiler room more combustion air but it seems like a very odd setup to me and I've been considering sealing off the boiler room from the rest of the house except for the wall vents to the basement using some insulation.

- There is one more gas appliance in the boiler room, the hot water tank, but it does not have a standing pilot either and is a power vent model which does not share the chimney at all and just vents out the side wall. Sometimes I feel as if the venting of the water tank is interfering with the draft of the boiler though since the power vent fan seems quite powerful.


What the two separate techs the HVAC company sent out about this have told me now is that leaving the damper open keeps the liner tempered and helps it keep the draft going which makes total sense. At the same time, they also had told me that the smaller properly sized and shaped liner would make it easy for the boiler to establish the draft even without this but it seems that this is not the case. I haven't been able to locate any information on the net that says that a natural draft boiler without a standing pilot cannot use an automatic damper.

I'm going to take the cardboard off of the vents that the chimney guy told me to put on... that no longer makes sense to me, but I am still considering closing up the ceiling space with insulation because now I'm thinking that opening the room directly to the next floor might be causing a stack effect to form in the room.

The location of the spill switch seems pretty normal to me and appears to be placed in the boiler factory supplied location which is on the front and a few inches under the flue hood. During the initial inspections I had asked them many times, is it possible it's just the spill switch and nobody thought it was... I was really hoping it was since a spill switch is both cheap and a snap to replace... perhaps I should just replace it myself regardless but doing anything with a gas appliance always gives me thoughts that I'd be doing something illegal...

I can take photos, but what should I take photos of exactly?

Any other insights appreciated!

HVACDave

Is there a long latteral run from the boiler to the vertical flue? How much striaght vertical vent comes off the top of the boiler (after the draft hood) before the elbow takes the venting to the chimney?

chiefswabjockey

No, it is pretty vertical all the way up into the chimney. There is maybe only 1 foot after the hood before the elbow out the wall but that was replaced by the chimney liner guy and it looks properly graded to me.

beenthere

Turn your thermostat down. let the house cool a bit. Then after its been idle for an hour or 2. have someone turn the thermostat up, while you are at the hood with a lit candle. See if its really spilling. Run the candle around the hood and see if its drafting out or not. If out, weak spill, if not. You need to have a barometric damper installed in the flue pipe to allow it to draft warm basement air out during its off cycles.