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amakarevic 09-02-2011 09:04 PM

venting radiator boiler through bigger vent
i am moving my radiator boiler and i mistakenly put the new venting in place using 6" vents. don't ask me how ... i just thought the old vents were 6 also but they were actually 5.

so my guess would be, under the bigger heading "the more the merrier" that there won't be problems venting this baby through a bigger vent pipe. the exhaust on top of the boiler is also 5. i can just get an adapter. i used type B venting.


hvac benny 09-02-2011 10:11 PM

I'll tell you what I tell my wife: "Bigger is not always better!" And with venting this is definitely the case. If the flue is too big, the gases may cool too much and condense before they leave the stack, ruining the vent and causing spillage. If you're already hooked up, you need to ensure that the flue draws. Sizing your flue is also very important, you can't just use the same size, there are other factors involved: height(from the top of the draft hood to the top of the vent), lateral, type of draft (natural or fan assist), and appliance input rating. This is assuming that it is the only appliance using this vent.

amakarevic 09-02-2011 10:32 PM

1 Attachment(s)
the chimney is about 15 ft but the vent pipes go about another 16 ft horizontally from the boiler until they get into the chimney. the pipe makes 3 bends on the way to the chimney. the old pipe was traveling a little less horizontally (maybe 12) but the chimney part was taller (it was in the basement before and i moved it to the 1st floor). and it made a really weird spiral (see picture) when it exited the appliance (dunno why). do you think i should make the spiral or can i just take it out in a straight shot ?

also, the chimney is also used for the water heater (40 gal) and both appliances are gas. but they don't share vents before they hit the chimney, each have a separate horizontal vent to the chimney.

so, with these specs, do you think i'll be fine?


REP 09-02-2011 10:59 PM

If the boiler is 5"then the flue should be 5"and it should be "B" vent all the way.
Does that effical damper still work? they have a sad history of going bad .If its bad then remove it.
It will be interesting to watch if for some reason you have to move the boiler 6" in any direction with where you put the gas cock.I may be wrong but I think you still need a drip leg.Since this is not a new boileer did you bore out the water tubes like you should every so often with that boiler?
Don't see your water feed or your LWCO.
Do you have fun going all over the house bleeding the air out as I see no air scoop or vent.That should be a" spiro vent" by the way.
I would never terminate the water blow off near the control wiring.

amakarevic 09-02-2011 11:04 PM

actually, i just measured the vent on top of the appliance and it is actually 6". but the old setup, which is what the picture shows, then reduces it to 5, for a reason unknown to me but i do know that whatever the old house owner did, he did wrong -- everything.

however, the first pipe out of the boiler before the reducer does not seem type B as it has crimping all around, i.e. looks more like a regular drier vent or something el cheapo. but i do think it came with the appliance cause it has some electrical device (i guess a blow inducer or something of the sort) attached to the pipe. since all my piping is type B, i guess i will need to find some adapter between ducts and type B vents (i hope there is such a thing).

REP 09-02-2011 11:10 PM

That electrical devise is the vent damper I mentioed.It probably doesn't work.

amakarevic 09-02-2011 11:14 PM


Originally Posted by REP (Post 720262)
That electrical devise is the vent damper I mentioed.It probably doesn't work.

what does it do when it does work?

REP 09-02-2011 11:23 PM


Originally Posted by amakarevic (Post 720263)
what does it do when it does work?

When the boiler is in the off position(not running) the disc on the end of that electrical device is flat across the vent opening on the boiler.This is to prevent the natural draft through the chimney from stealing all the heat in the boiler water.When the thermostat call for heat the disc rotates so that it is up and down in the discharge flue allowing the hot gas to vent to the chimney.

amakarevic 09-03-2011 12:07 AM

what do you think about that tail pipe to which the damper goes not being type B and looking like a plain duct (crimping) ??

amakarevic 09-21-2011 10:43 AM

i posted another, related, question. i thought that those of you you replied to this might know the answer.


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