Can I vent Combi Boiler through chimney with PVC?

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mdk0420

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I'm pretty far with my Combi Boiler install. I think it is looking pretty nice. I am trying to tackle the future issue of running the vent and intake which will have to utilize 8 elbows and a 55' run and even then, I'm not sure if it would pass because of the clearances. Looking at the manual for the Navien NCB-180 there are a lot of clearances I have to meet which is making it difficult to place a vent and intake anywhere along my sidewall.

To help paint a picture I have a concrete porch that wraps around to the side of a duplex style home, with a portion of the side being dedicated to meters and boxes (the manual says I can't be within 48" of a meter). Going to the rear of the duplex is a wooden porch up to a stairway that leads to the basement. The borough said they would prefer I don't run it under the porch (Makes sense because who wants to breath carbon monoxide venting out while relaxing on your porch). Plus there is a mostly fixed which, however it has a little venting piece attached to it which would probably make it an operable window and require it to be 4' from that. I could probably work around that and put it off to the side though. The other place I was hoping to put it is almost 4' away from the kitchen window right off to the side of the basement steps, but then "almost" isn't quite enough. On top of that my manual says not to stack the venting and putting them side by side at 12" apart would be very difficult there.

So I thought to myself that I would love to use the chimney, but without having to line the whole thing. Would running PVC pipe inside the chimney be allowed? There are no other uses for the chimney except for the old boiler that is being replaced with the combi boiler. Instead of spending all the money to line the chimney (Switching from oil to natural gas) I was hoping to just run either 2" or 3" PVC pipe depending on the distance. I'm not sure if this is ok though. I also don't know how I would do it... I've never done roofing so I'm not familiar with the techniques used to keep rain from entering an exhaust, or does it not matter? Would I simply elbow them opposite of each other facing down? Thanks for any info on this ahead of time!

Here's a picture of my work so far!

21ovwpf.jpg
 
It does not appear that you will have the height to get your vent piping over to the chimney, with the min. 1/4"/ft. slope. If you could make it, I don't see any other reason why you could not use the chimney as a chase.
[Do consider that if you don't air seal at least at the top of the chimney, you will constantly be leaking warm air out of your house in winter. If you do air seal at the top, you will still have convective currents leaking heat (warm air, being less dense, will rise above colder air. When the warm air rises to the top (pushing colder air down), it is cooled by the cold chimney and then sinks. That is a convective current.]
I don't understand some of the other restrictions that you noted. You only have to be >12" from an operable window or door, not 4 ft., although you would not want it to vent just below a window because you would not want to see the plume of vapor in the winter. Why not use a concentric termination to avoid having to space the in and out apart? Read the venting section of the manual again.
 
frodo said:
View attachment 17953

expansion tank needs a strap, it gets heavy full of wa wa
Click to expand...

Not at all thanks for the feedback. It's the first time installing a boiler, let alone first time even soldering so it should be interesting when I go to fill her up... I'm expecting some leaks but I think most of the joints look pretty solid. I'll try to answer some of your feedback.

The circulator was installed this way with the older boiler. I Have a backup circulator as well and there are actually designed in setups that might look like flaws but I did that on purpose (Except for the ballvalve on the bypass being crooked lol). I actually have the supply line with the circulator coming out a little bit to allow the circulator to fit. It was a little to close to the wall. I also pushed the return line Tee right against the wall because my backup circulator secures to the flanges at a 90 degree, making the motor go to the side. This gives it clearance for either style motor to work as it can go over the return line. But in the end, I have no clue if that circulator is actually allowed to be that way. I just kept it the same orientation as before. It's probably pretty old lol. But I have two circulators that I want to run until they fail until I get a new one.

The backflow preventer has no mention of orientation. Just the specs and some tips on where to install.

I never knew that about the ballvalves! That's very interesting. I did want them all pointing one way, which happened to be the opposite of the direction of the supply flow lol. I wanted them all to go clockwise but I couldn't because of the clearances between the piping and I planned this to be a fairly tight system to minimize space taken. I actually didn't think I was going to have enough room to install the circulator like I wanted too but I just made it. So spaces like where the air separator I actually had to have one valve go one way and the other go the other way because it elbows away from the wall to allow clearance to put the expansion tank in there.

Speaking of expansion tank, I was thinking about using a strap but I noticed most of the systems that I looked at didn't have theirs strapped when hanging like this. I did give it some extra support though with 2 support brackets that connect on each side of the air separator. I did that because I didn't feel safe with the extra leverage from elbowing it outwards to make room for the expansion tank. It feels really sturdy and those are 3/8 inch rods holding that bracket. Shouldn't have a problem supporting the weight. I might still put a strap on it if it feels unsecured though.

I used a level to put each pipe in place. I think its just the camera angle that is making it look like its not straight. But it is very straight otherwise. It's also not really secured on the potable water side yet because I'm still working on getting the lines done. It's also possible that since none of the split rings are tightened down it might be a little lopsided but it'll correct itself once I tighten everything down.

And lastly, the obvious look of the cold water line lol. I actually did that purposely so that the hot water water line can go over the cold water line. I wanted to extend faucets off to the side and I needed them to cross. They also will be crossing at the top because the cold water line is on the right side and the hot water supply is on the left. I started cutting some pipe to length as you can see for the cold water line. But the hot water line is running on the opposite side of that joist opening.

One more thing to note, the expansion tank is only going to be like that during the testing and inspection phase of things. I have the 1/2" ball valve with drain on its way but it is backordered. I'll have a 1/2" nipple coming off of the air separator, then going to the ball valve with drain and the expansion. I originally ordered a setup for a 3/4" ball valve because in the description for the expansion tank it said it was a 3/4" fitting. It was 1/2" though so now I'm just waiting on the parts. It should function just fine this way for the inspection though.

I'll tell you what, those isolator valve kits that have the red/blue purge vales really irked me lol. If you notice I had to turn them to the side and I had to have them almost absolutely perfect to be able to turn all the butterfly valves on and off and still be able to get a relief valve in there. That was insane. On top of all that I don't even know if it'll be ok like that. I'm hoping it will otherwise I have to extend the hot water line down so I can elbow the relief valve vertically, but from what I understand hot water heaters are allowed to be horizontal, which I would think is what that part of the piping would be considered. We'll see if the inspector flags it or not.
 
Last edited:
fixitron said:
It does not appear that you will have the height to get your vent piping over to the chimney, with the min. 1/4"/ft. slope. If you could make it, I don't see any other reason why you could not use the chimney as a chase.
[Do consider that if you don't air seal at least at the top of the chimney, you will constantly be leaking warm air out of your house in winter. If you do air seal at the top, you will still have convective currents leaking heat (warm air, being less dense, will rise above colder air. When the warm air rises to the top (pushing colder air down), it is cooled by the cold chimney and then sinks. That is a convective current.]
I don't understand some of the other restrictions that you noted. You only have to be >12" from an operable window or door, not 4 ft., although you would not want it to vent just below a window because you would not want to see the plume of vapor in the winter. Why not use a concentric termination to avoid having to space the in and out apart? Read the venting section of the manual again.
Click to expand...

The chimney is only 3 feet from the boiler (add a foot or so for the exhaust vents distance). I lowered it 15" to be able to make the run to the rear of the house. UGH! I was reading the wrong section of the book when I mentioned the 4'. I was looking at the "Non-Direct Vent" section. Yes you are correct, it looks to be 12" of clearance to any operable windows or doors. I'm also going to use a section of CPVC for the first couple of feet. I'm still pretty fond of the idea to direct vent it through the chimney though.

By concentric termination do you mean the dual setup where the intake and exhaust are on piping at the end? I saw that in the manual but it wouldn't work in the area placed to the rear of the home unless I drilled through the concrete instead of the wood joist. I was planning on just elbowing up and then another elbow straight out. I have a hole saw for the wood but nothing that is big enough to drill through the concrete, thoguh I guess it could be an option.

I also can't find anything about the 4' rule away from the meters anymore... idk where I read that at. I'll have to call the township tomorrow and ask if it would be possible to run it out to where the rest of the utility boxes are. The gas company was complaining about how close they were to the electric meters, but there really wasn't anywhere else for them to put it so they placed it just a couple of feet away from them lol. This would allow me to run with the joists so I could actually install a system like that through the side. In either case the longest run is 55" and I'll have enough slope to make it the whole way.

On a side note, my manual says that the venting must be connected every 4'. Why would I have to do that if it would be safe to have one solid 10' run? I'll have to ask the township about this as well. Would like your opinions on it.
 
I talked to the inspector and he mentioned a double wall pipe as well being needed as expected from your advice, frodo. But that there is no other problems with it otherwise. If I were to do that, is there anything I should consider? I'm guessing condensation isn't an issue since the boiler is designed to handle that as part of its efficiency. I'm guessing the chimney would stay relatively warmer then the outside air as well since I would cap the chimney, but is there any steps I should take incase of freezing? I live in PA. Usually the winters are around 0 degrees f or so, maybe slightly into the negatives on bad winters (Or wind chill). Or any other issues that I might need to take care of like securing the pipe? Is securing the pipe at the base and the top enough for whats roughly a 40 foot run?
 
frodo said:
i would use a tee at the bottom of the vent stack for condensation and 2 riser clamps to hold the stack
along with 2 pieces of 2'' angle iron spanning the top of the chimney, to rest the riser clamp on

View attachment 17985
Click to expand...

Is it necessary to have it escape away from the boiler or can a condensating boiler handle that issue without the tee? Although it makes sense that the exhaust should float up I don't know how I feel about a line coming back into the house. If it is necessary though then I'll make it work. I was hoping that if the condensate comes back through the exhaust then it'll just drain into the condensate bowl and go through the condensate drain on the boiler. Should be easy to use your support idea. I can get some decent access with the old hole as well.
 
The flue pipe should be soild pipe untill termination. If its a condensing unit then the unit should be able to handle the condensate. Making your own drain is unnecessary.
 
You might want to look into the price of a re-liner kit for the chimney as double wall pipe is pretty pricey too.
 
I am a level 3 trained by Navien.
You can NOT line a chimney for a condensing appliance. It has to be piped.

The vent pipe has to be solid 2" PVC (or the other material mentioned in the Navien manual CPVC (expensive -, even the new/expensive? Centrotherm Inno Flue flex) and drain backward towards the appliance - where the condensate is then drained or pumped out.
No tee need be used (though the Centrotherm diagram on page 33. shows a tee, but it would need to just be as a support, be capped and condensate would overflow into the horizontal line).
If you supported the capped tee, then you shouldn't need the riser clamp on the top.
I have used a riser clamp on the low end, but that is a pain to do structurally.

There is no such thing as double wall pipe for any of this.

You can bang out a new hole in the chimney to make working on fittings easier.
You can use the low horizontal run you described for the intake air, even under the porch if it has screened openings or some full air flow source, and use the plastic screen Navien ships.
Always use the screens on both intake and exhaust. ( I made $250. pulling a dead rat out of one that did not have the screen just last month)
Marc
 
breplum said:
I am a level 3 trained by Navien.
You can NOT line a chimney for a condensing appliance. It has to be piped.

The vent pipe has to be solid 2" PVC (or the other material mentioned in the Navien manual CPVC (expensive -, even the new/expensive? Centrotherm Inno Flue flex) and drain backward towards the appliance - where the condensate is then drained or pumped out.
No tee need be used (though the Centrotherm diagram on page 33. shows a tee, but it would need to just be as a support, be capped and condensate would overflow into the horizontal line).
If you supported the capped tee, then you shouldn't need the riser clamp on the top.
I have used a riser clamp on the low end, but that is a pain to do structurally.

There is no such thing as double wall pipe for any of this.

You can bang out a new hole in the chimney to make working on fittings easier.
You can use the low horizontal run you described for the intake air, even under the porch if it has screened openings or some full air flow source, and use the plastic screen Navien ships.
Always use the screens on both intake and exhaust. ( I made $250. pulling a dead rat out of one that did not have the screen just last month)
Marc
Click to expand...

My township inspector said I cannot use PVC or cpvc inside the chimney. He said there have been cases of people cutting off the connection to a PVC ran appliance, then covering it up and leaving the piping there, eventually a new appliance makes it way to using the chimney and starting a fire. He said I have to use double wall piping to use the chimney.

I heard there can be issues if pressure differentials by having the exhaust and intake in different places but i don't see anything actually mentioned in the manual so I assume it would be allowed. I found out from my township that I only need to be 30" away from the meters which I might be able to clear that distance. I forgot to ask what the snow height is since I also need to be 12" above the anticipated snow level.
 
Your inspector is an ignorant, uneducated-in-this-case, backward thinking boob. I would go over his head to the senior mechanical inspector. Or have the local Navien rep talk to him.

There is no "double wall" plastic. And what would it be for, an 80% efficient dinosaur?
You can not use any metal double wall with any highly efficient condensing appliance.
 
breplum said:
Your inspector is an ignorant, uneducated-in-this-case, backward thinking boob. I would go over his head to the senior mechanical inspector. Or have the local Navien rep talk to him.

There is no "double wall" plastic. And what would it be for, an 80% efficient dinosaur?
You can not use any metal double wall with any highly efficient condensing appliance.
Click to expand...

That is fine and dandy. He can be wrong all he wants but he is the inspector and he will fail me, whether or not it makes sense it is his decision. I won't be putting PVC in the chimney. I would use double walled venting for the chimney because that is what he said I would need to do to make it pass. But I might just give up the idea of the chimney.

I just hate the idea of running the piping through my basement. I had to have it about 14" below the joist and it has to come away from the wall about 30" to get passed the chimney and passed an electrical box, unless it is structurally safe to drill 2 3" holds on both sides. It'll put the piping at shoulders length for a good portion of the basement run. I can have a total of 8 90 degree elbows. I'm assuming 2 45's would = 1 90? If that's the case I could use the street 90 right from the boiler coming out about 20" to clear the chimney, use 3 more elbows to go around the chimney and back against the wall, at the end of its 20' or so run, I would need to elbow along the utility room, which has an electrical box on the other side. It needs a minimum of 3' clearance from that panel. I'd elbow it back in, run it several feet into the utility room at that point it'll only be a few inches under the joist where it'll use 2 45 degree elbows to offset to get it into position to go into a concentric system outside. I'll see if I can make a drawing of that lol, but either case that is what I'm trying to avoid... The chimney seemed to take the least clutter but I'm confused why I can't use a double vent wall. Doesn't it use the condensate inside the system, not in the flue? Even a double wall vent would have condensate as well though wouldn't it?
 
Most inspectors will accept the factory recommendation
call your boiler 800 number and talk to a tech about your particular situation.
have him write up his directions and sign it, then, before installing, run it past the boiler inspector

i do not know your township laws, but running a pvc line in a chimney is a huge no no
bad ju ju, upsets the chi balance of the Walrus
Goo goo g'joob goo goo g'joob
[Beatles Reference]
 
frodo said:
Most inspectors will accept the factory recommendation
call your boiler 800 number and talk to a tech about your particular situation.
have him write up his directions and sign it, then, before installing, run it past the boiler inspector

i do not know your township laws, but running a pvc line in a chimney is a huge no no
bad ju ju, upsets the chi balance of the Walrus
Goo goo g'joob goo goo g'joob
[Beatles Reference]
Click to expand...

Lol yeah the inspector explained why it is such a bad idea to run the PVC inside the chimney. It just takes one person to cut off and cover the PVC pipe entrance and then randomly put in a new flue and now you have a fire hazard. Makes sense. Definitely won't be running PVC up the chimney. Im trying to find out what is wrong with running a double wall vent up the chimney or even just lining the chimney and venting it. How would that effect the efficiency of the boiler?
 
That boiler creates condensation in the flue gas you cannot use any metal venting and you cannot have it venting to a lined chimney it needs to be PVC all the way to the exterior of the house pitchedback towards the unit plain and simple done and done
 
Vent according to local authorities & unit manual specs. No Shortcuts (void warranty&call manufacturer)after all your nice work, sounds like u may have no choice but a chimney liner....
 
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