Options for combining boiler vent pipe with water heater vent pipe into chimney

codyr

Hello, I’m installing a new gas boiler (input BTU: 74,000) with a draft hood that uses a 5” vent pipe. I currently have a water heater (input BTU: 75,100) that has a draft hood which has a run of maybe 7’ of 4” vent pipe that enters a masonry chimney. Chimney height is maybe 40’. I’m wondering what my options are for venting the new boiler into the chimney. I didn’t know if I could reduce the 5” into a 4” wye and attach the wye to the 4” that already enters the chimney (that the water heater is using)? Or do I have to tear out the mortar/4” that is going into the chimney and replace with a 5” manifold/wye? I attached some pics - the yellow circle is where the boiler vent pipe exists straight up. The arrow is where the 4” from the water heater enters the chimney.

-Cody

neilc

what is that larger vent lower left doing?
don't say fresh air !

codyr

neilc said:

what is that larger vent lower left doing?
don't say fresh air !

Good question. I have no idea! It’s 6” pipe that appears to link the return side of my forced air ductwork into the chimney.

neilc

o m g
let me spell that out,
OH MY GOD !!!

outside on the base of the chimney, is there a louvred vent opening?
please?

or are you drawing from where the bad stuff is exiting ?

you need a chimney guy there,
and you need CO detectors, tonight

codyr

neilc said:

o m g
let me spell that out,
OH MY GOD !!!

outside on the base of the chimney, is there a louvred vent opening?
please?

or are you drawing from where the bad stuff is exiting ?

you need a chimney guy there,
and you need CO detectors, tonight

Sorry, I should have I given a little more info. That boiler in the picture is the old one that I took out, it had its own dedicated pvc vent pipe that went out the side of the house (not to current code). The yellow circle I drew is approximately where the new boiler’s 5” vent pipe will exit upright from the draft hood. No louvered vent opening that I know of at the base. The house has a gas fireplace in the basement, 1st, and 2nd floor. I believe there are 4 separate chimney flues that exit out the roof (all next to each other ).

Bob Harper

You need to install a 5.5" stainless steel chimney liner to a manifold at the wall. The manifold should be a 6" uphill with 5"x5" take-offs. You run 5" pipe back to the WH sloping 1/4" per LF until over the draft hood then drop down vertically, effectively moving that elbow off the draft hood and raising it as high as possible. Since it is CMU block wall, have the liner brought out maintaining a 6" clearance to the combustibles above to maximize vent rise. The connector to the boiler will be lower so the 5" should be sufficient vent rise not to increase the connector diameter. You go bigger on the connectors- never smaller.
Now, as for that insane return duct. It must be disconnected and shut off at once. That is a carbon monoxide distribution system. Whomever did that should go to jail.
You need a low level CO monitor ASAP.

neilc

yeah, forget the yellow, and pvc,
it looks like you're drawing fresh air in thru the chimney, thru a flue run, to your furnace return,
and you're drawing the furnace air(OA) from the top of the chimney where all the CO and exhaust spills out,
that's BAD

codyr

Bob Harper said:

You need to install a 5.5" stainless steel chimney liner to a manifold at the wall. The manifold should be a 6" uphill with 5"x5" take-offs. You run 5" pipe back to the WH sloping 1/4" per LF until over the draft hood then drop down vertically, effectively moving that elbow off the draft hood and raising it as high as possible. Since it is CMU block wall, have the liner brought out maintaining a 6" clearance to the combustibles above to maximize vent rise. The connector to the boiler will be lower so the 5" should be sufficient vent rise not to increase the connector diameter. You go bigger on the connectors- never smaller.
Now, as for that insane return duct. It must be disconnected and shut off at once. That is a carbon monoxide distribution system. Whomever did that should go to jail.
You need a low level CO monitor ASAP.

Ok, first off thanks so much for your time and response! Is there a way I can confirm that that 6” return duct into the chimney is a CO distribution system? I first thought about capping it at the ceiling where it enters the return ductwork, and using the existing hole in the CMU where the other end is to actually vent my new 5” boiler pipe, would that work? Since I didn’t know what the purpose of that 6” pipe was I didn’t want to mess with it yet.

codyr

neilc said:

yeah, forget the yellow, and pvc,
it looks like you're drawing fresh air in thru the chimney, thru a flue run, to your furnace return,
and you're drawing the furnace air(OA) from the top of the chimney where all the CO and exhaust spills out,
that's BAD

neilc said:

yeah, forget the yellow, and pvc,
it looks like you're drawing fresh air in thru the chimney, thru a flue run, to your furnace return,
and you're drawing the furnace air(OA) from the top of the chimney where all the CO and exhaust spills out,
that's BAD

Thank you for helping me with this, much appreciated. I somewhat understand what you’re saying, but wouldn’t the furnace CO/exhaust air not be an issue since that exits through the pvc pipe out the side of my house? (And not the top through a chimney). if I had a gas fireplace going, I could maybe see that being an issue.

neilc

That 6 inch, connected to the furnace return duct, is sucking air down the chimney, from the top, where all the other flues are dumping CO exhaust,
you wouldn't go up there and breath from the top of the chimney, right?
What's coming out the top of the other flues is likely getting sucked right back down into the furnace.

This is nothing to do with the furnace exhaust going out the pvc.

Do you use the gas fireplaces?
(and the furnace runs at the same time)

CO detectors

codyr

neilc said:

That 6 inch, connected to the furnace return duct, is sucking air down the chimney, from the top, where all the other flues are dumping CO exhaust,
you wouldn't go up there and breath from the top of the chimney, right?
What's coming out the top of the other flues is likely getting sucked right back down into the furnace.

This is nothing to do with the furnace exhaust going out the pvc.

Do you use the gas fireplaces?
(and the furnace runs at the same time)

CO detectors

I understand, I wasn’t thinking about the WH and fireplace exhaust up there as well. I have CO detectors down there and near the sleeping areas. Do you know why something like this would have been installed in the first place if it’s so dangerous?

neilc

hell,
the furnace wouldn't even need to be running,

stack affect, cold goes to the basement first, then is drawn out the top of the house thru all the holes, fireplaces, etc.

while the gas fireplace(s) are running, cold air could drop in the furnace fresh air flue as make up air and distribute thru the ductworks,

https://forum.heatinghelp.com/discussion/182396/co-alarms

codyr

I disconnected the vent that goes from the return on my furnace into the chimney (it’s 7”). I ran a camera up and took some pics. Does anyone know if I’m able to just use this existing hole to vent the boiler (reduce down to my 5” boiler vent pipe?) Thanks 

neilc

you're not gonna like these answers and questions,

was the "up chase" picture taken during the day?
cuz I don't see it going to daylight, like at the top of a chimney,

and now me thinks it is a working return duct to upper floors,
how many stories is the house?
what returns do you see upstairs aligning with that chimney area or chase?
it's dirty dusty like a return duct would be.
jam a garden hose, or electrician snake up that duct and rattle it, where do you hear it upstairs? or ask a plumber / drain guy to send their inspection camera up to its end.

No, you can't use that as your boiler or furnace exhaust,

consider this also,
if that is a working return, and you have compromised working exhaust inside that same masonry assembly, if the flue is compromised that CO could still get sucked across and back to the return, to be distributed through the furnace, NOT GOOD.

tell us you have working CO detectors.
I like the Kidde's with digital readout,
and yes, I check the "Peak" button daily.

codyr

neilc said:

you're not gonna like these answers and questions, was the "up chase" picture taken during the day? cuz I don't see it going to daylight, like at the top of a chimney, and now me thinks it is a working return duct to upper floors, how many stories is the house? what returns do you see upstairs aligning with that chimney area or chase? it's dirty dusty like a return duct would be. jam a garden hose, or electrician snake up that duct and rattle it, where do you hear it upstairs? or ask a plumber / drain guy to send their inspection camera up to its end. No, you can't use that as your boiler or furnace exhaust, consider this also, if that is a working return, and you have compromised working exhaust inside that same masonry assembly, if the flue is compromised that CO could still get sucked across and back to the return, to be distributed through the furnace, NOT GOOD. tell us you have working CO detectors. I like the Kidde's with digital readout, and yes, I check the "Peak" button daily.

Like I said in a previous reply, I do have CO detectors in the basement in addition to ones in all of the bedrooms, I appreciate the thought though. The picture was taken during the day, my Chimneys are all capped at the top, but I did still expect to see some kind of sunlight. I didn’t stick the camera up more than a couple feet. My house has a walkout basement with a 1st floor and half 2nd floor. The room inside that the centrally located chimney is in goes all the way up to the roof from the 1st floor. I do see a return vent next to the chimney column. I’m going to try to stick a fish tape up that chimney run from the basement and see if I hear anything upstairs. If this is a working return, are those not done anymore? Were they ever ok to do? Thanks for the suggestion! 

PC7060

Make an appointment and have a chimney inspector come over. They’ll look at the whole system and give you a report for about 125 bucks.