Venting a condensing boiler?

[DocsMachine]

We're shortly going to be working on a furnace replacement project, taking out an older and well-worn boiler and replacing it with a more modern condensing boiler.

The current flue is of course a straight chimney- double wall metalbestos, I think?- that goes straight up and through the roof. The homeowner would like to use that passage to vent the new boiler, rather than cut another hole in the wall (concrete basement, 2-story) for a side vent.

Could we get away with somehow just running a poly pipe up the current chimney? Or would it be better to fully remove all the old metalbestos and somehow mount/attach the poly.

Or would it be better overall to go sideways through the wall? The biggest problem there is that the easiest (and really, one of the few possible) routes puts the vent near the front door of the house.

If we can run it up the chimney, or in that passage anyway, what's the best way to support it? Anything else we need to be concerned with?

Doc.

 

[PoorUB]

The problem I see is running both the exhaust and air intake in the chimney. I doubt you have room for both pipes. If you do, then go ahead. As for support, just make sure the bottom is supported well, preferably blocking or something under a 90 degree elbow at the bottom. The rest of the run will be fine. Cap the chimney with sheet metal with holes for the venting.

 

[Jackfre]

As PoorUB points out, the issue is both pipes. Can it be done? Yes, but you need to closely follow the instruction of the boiler manuf instructions, so pick the boiler first and then figure out your options. I think that most of the gas boilers using a negative pressure gas valve will allow you to have the intake and exhaust terminations in different pressure zones, so you can run the exhaust up the stack and then run the intake out the side wall or wherever. We don’t know where you are but be aware that PVC is starting to be banned. So far it is NH and MA who have done so, but it will likely grow, as pvc is not an approved vent material. Centrotherm is the better option.

 

[DocsMachine]

Thanks guys, that was quite helpful. We also found Dura-Vent, which appears to be a sort of liner specifically for this kind of thing. Anyone have experience with that?

Doc.

 

[yeldogt]

You can go up w/ duel through the chimney -- some of the twin tubing is expensive. Most boilers allow for the flue to go up and the intake to come in from the side wall ... I often do it that way as I like designing my buildings with lots of windows and it can be hard to find a flue spot -- plus I would rather not see it in the winter. The single pipe up is also easier to hide.

Often the best way is a concentric through the side wall ...larger the boiler the more gas will come out so that's a thing to think about

 

[DocsMachine]

We were apparently starting to lean that way. Exhaust up the current chimney, but a separate intake out the front wall. We just didn't want an intake AND exhaust right near the front door.

Another question (keeping in mind all parties involved are very new at this ) what will we need for a drain? We're going to have to go overhead to connect to a wastewater drain, so we'll need... what, a collection tank and a lift pump? What are we looking at, here? Personally, I don't even know the terms to Google...

Doc.

 

[PoorUB]

How it is vented really depends on the unit you buy. One will vent in 2" the next one needs 3". One can pull air from one side or the building and exhaust out the other, the next will be very specific about having the intake and exhaust a few inches apart where the exit the building. Pretty much anything we say without knowing a specific model is just guessing.

 

[Bert_]

I can understand. I'm not a fan of a bunch of pipes sticking through the wall.

The pump you want is called a condensate pump. Very common

 

[Jackfre]

The proper way to dispose of the condensate is to go from the boiler drain to a neutralizer to the condensate pump. The neutralizer is filled with consumable limestone chips. Untreated the pH on condensate is about 3.2, so pretty hot and not to be taken lightly. It will eat concrete.