Boiler vent letting fresh air in

larryjbjr

Ok, here are a couple pics of where the vent from my boiler goes thru the foundation. As you can see there are several holes in it and the wind just blows right thru them into the basement. Can someone tell me how to go about sealing that up? What could I use that won't catch fire?

Mark Eatherton

You can't block those holes. They are there to cool off the pipe and to keep it from causing a fire.

ME

Abracadabra

Doesn't that thimble look like it's the wrong size for the pipe?
Also, corrosion seen on first pipe. Does vent have the right pitch?

MilanD

When you say vent, is this flue or main with water/steam?

If it's flue, I'm not sure what can be used with a high flash point.

As for steam/water, isn't wood flash point 572 F? Can a 212 degree pipe cause a fire? If this is not some kind of deliberate venting, I'd assume you can use any insulation batting. I'd probably do one without a vapor barier so not to cause moisture issue in the cavity and on the pipe.

Where is this pipe going to if it's going through the foundation wall? What is on the other side?

It also looks like someone clamped that pipe to repair a leak at some point. Check the pipe for sag. Even a small amount of water sitting there may accelerate rusting of the iron.

MilanD

Ok. Ok. Now I see. It's flue pipe... Hot, higher than 500 F... Careful with that.

MilanD

Also, this will help with cobustion air in the basement and with draft. I sometimes have to crack a small plastic window in my glas block basement windows to get the water heater to not backdraft on esp. cold days.

captainco

I do believe knowing what type of boiler this is would have been helpful. Is it induced draft or condensing. Is it just sidewall vented or does the flue go vertical on the outside? Also considering the size openings we normally install for combustion air, I would think those tiny holes can be that big of a deal.

larryjbjr

It's a Burnham boiler model P-205PV-WPI. It does have a draft inducer.

It is the flue. I just checked it this morning with my IR thermometer after it had been running maybe 15 minutes. The Temp was only about 170 F. So, that's not too hot, huh?


@captainco, Well, it's not just the holes in the thimble. Maybe I didn't make myself clear, my entire old part of the basement has drafts around foundation. Everywhere else I have stuffed fiberglass insulation in between the logs to stop the drafts. This spot is no exception, there is quite a draft coming thru! I don't think it's just the holes in the thimble. I was just afraid to stuff insulation around that part in fear of coming in to contact with the flue pipe.

larryjbjr

@Abracadabra, I don't know what the right pitch should be, but it is inclined quite a bit.

@MilanD, it goes thru the foundation beam and just terminates about a foot from the house. It has some kind of cap on it that is open on 2 sides horizontally.

MilanD

As @captainco said, combustion air inlet (as opposed to keeping a window in the basement cracked). At some point you need fresh air for the device to burn fuel, and this makes sure it's coming from somewhere. It may even be a code in some areas with through-the-sill / wood sill / flue venting, to prevent fire.

I am wondering if:

1. There is a way to run the flue through the brick/slab. You can then mortar around it and then 2. if there is any way to bring fresh air to the burners via another method, or 3, install some kind of motorized flue damper in that hole and around the pipe, on a switch like any other flue damper, and then have it open automatically before any combustion commences.

Otherwise, if you insulated all around the basement except for that pipe, it may be that you will just have to live with it. You may try foam insulation against the sill all around the basement, and that would get into all cracks and crevices and significantly reduce air infiltration from other areas in the basement.

But you have to have combustion air come from somewhere. Again, I crack a small window in my basement to help with draft on my hot water heater in winter months (my furnace is high efficiency with PVC air intake and exhaust). Otherwise the cold fresh air may find a different way to get in (as happened to me once), and that would often be through the flue, which is what backdrafting is. This could quickly get the CO levels deadly, esp on a furnace which uses much more o2/air to heat the whole building, vs. the water heater. But, both need proper draft.

While at it, I would install a CO monitor both in the basement, and in your bedroom, in case you don't have one.

Best of luck!

John Mills_5

Hopefully that's stainless steel not single wall galvanized.

MilanD

You said you have a draft inducer on that Burnham? You mean canopy blower? I believe this is only to help with draft, not with bringing air to burners. Can you show the picture of that set-up? Manual for this model says it's a draft hood version and I am curious how is the inducer set-up, if you in fact mean inducer and not draft blower? Potato, tomato...

Mark Eatherton

Build it tight and vent it right. Check with the applicable code in your jurisdiction, and if none exists, give it 1 square inch free combustion air per 4,000 BtuH INPUT capacity.

Dip incoming air 6" into a 5 gallon bucket and create a cold air trap. Also, when using an IR thermometer, if using it on a shiny metallic pipe, it is giving a false low reading. Dull the surface with flat black paint to get a truer indication of surface temperatures.

ME

captainco

If the boiler is operating correctly the flue temperature should be 330 to 430 degrees. I do believe the flash point of wood will get lower with age and exposure to heat. If it is vented in B-vent it only needs a 1" clearance from combustibles and that would be without the holes in the thimble. If it is single wall pipe then it is better the way it is.

Code state you need 50 cu.ft. of combustion air per 1000 btus or 200 cu.ft. of combustion air per 4000 btus. 200 cu.ft. of air is 345,600 cu.in of air. Apparently a 1" hole in the wall will bring that in? When you do the math it doesn't sound logical.

larryjbjr

MilanD said:

You said you have a draft inducer on that Burnham? You mean canopy blower? I believe this is only to help with draft, not with bringing air to burners. Can you show the picture of that set-up? Manual for this model says it's a draft hood version and I am curious how is the inducer set-up, if you in fact mean inducer and not draft blower? Potato, tomato...

I do not have a Draft Hood. What I have is a blower mounted just inside the unit under where the flue comes out. I had a repair man just a couple weeks ago came in to check out a loud vibration sound. He replaced that blower motor and called it a Draft Inducer. That's all I know.

MilanD

@Mark Eatherton

Thank you for the idea. Had some backdrafting on hwh, fixed pitch and sealed around flue and chimney area, and your comment had me build this contraption for good measure and to try it out. Plan is to insulate it a bit, and eventually replace the double cardboard box with something more pemanent.

Thanks!