Direct Vent Exhaust - Horizontal Termination - Insulation?

[OldSaltUSNR]

Pictures are attached, which may better explain what I'm trying to say with all these words below.

I have a MLDV500PSC direct vent fireplace (formerly Majestic, now Vermont Castings). During my home build, my HVAC crew installed my horizontal vent using an appropriate venting cap kit. They installed a DVP-WS firestop face plate on the interior. I had installed R19 insulation and drywall inside the void for the fireplace. The HVAC crew cut a hole in the drywall, from stud to stud, and slapped the DVP-WS over the opening, leaving large gaps to either side. It would have been nice if they'd been a bit more circumspect in their hole cutting, and matched the hole to the vent face plate, since most of the documentation I've seen requires only an inch of clearance between the sides of the pipe, and combustibles. I am aware that I can't stuff insulation into the void between the wall (studs & drywall), and that vent pipe, as that's a fire hazard.

For background, I've disassembled the temporary surround we had, to install a permanent masonry surround and ledgestone trim. I'm backtracking now, sealing all cracks and penetrations that could be leaking cold air into the insulated void, before I close it up for good. The fireplace appliance is ice cold during winter, which I'm given to understand is pretty much standard for these appliances, since the exhaust is essentially a inner and outer pipe connecting a metal box to the open air outside. I'm just trying to eliminate any unnecessary air penetrations, to minimize this problem.

I'd appreciate any informed suggestions, such as:

• Just leave it be.
• Stuffing rock wool insulation next to that pipe is A-Ok.
• Remove and reinstall the vent face plate properly into a SQUARE hole, i.e. pull the face plate, fix the drywall, and reinstall plate, but don't put insulation into the void between pipe and studs, so that your house doesn't burn down.
• Drink more beer; Then it won't bother you so much.

This "fireplace surround" project scope has expanded five times since I've started, and the very last thing I wanted to do is mess with that vent. The unit is about 160 lbs. If I have to work on the vent, it means pulling that unit, without impinging the gas and electrical lines. I can get that done; it's not rocket science, but it'll sure cut (yet another) hole in my project schedule.

Thanks in advance, for the advice.

Picture legend: Vent view from top/rear of the fireplace insert, close up of left/right side of vent face plate (and wall void), right side of void showing the heat shield behind the face plate, and finally, view of top heat shield and pipe, behind the face plate. Final picture is context, what the fireplace looks like as I tear down the surround and rebuild it (you can see the horizontal vent in the rear).

 

[DAKSY]

From an installer's point of view, that's just wrong. If you can't get the original HVAC
"professionals" to make that install to code, here's what I'd do - from the INSIDE -
WITHOUT pulling the unit & leaving the cap installed (if possible).
Remove the screws & & pull the horizontal firestop as far away from the wall as you can.
Determine where the one inch clearance to combustibles (CTC)is & scribe lines on the
horizontal framing members to either side of the outside if the outer pipe.
Install matching framing members (2x4? 2x6?) vertically & to the OUTSIDE of your lines,
making sure they are plumb & with 3" drywall or deck screws, fasten to the horizontal framing.
Install fiberglass insulation in the gaps between the new framing & the old.
Install small pieces if drywall or plywood covering the insulation & frame, seal any gaps with aluminum tape.
Reinstall the firestop & secure it. Seal the gap between the firestop & venting with aluminum tape.
While you have access to either side & the rear of the metal fireplace, seal any seams or holes with aluminum tape.
That includes the gas & electrical holes, and any gaps in the drywall, as well.
Do you know if there's insulation on top of the drywall above the firebox?
There should be. Kraft faced with the paper side down.
If there isn't, I would build ANOTHER deck, just above the A shaped stand-offs with
1/2" drywall laying on a band of 2x4s screwed to the existing framing, & insulate that.
If you aren't clear on ANYTHING I've stated, just ask me to clarify.
I installed as many as 20 ZC DV units a week for a couple of years,
& you want that area as sealed as possible to mitigate cold air penetration.
Good luck!

 

[OldSaltUSNR]

From an installer's point of view, that's just wrong. If you can't get the original HVAC
"professionals" to make that install to code, here's what I'd do - from the INSIDE -
WITHOUT pulling the unit & leaving the cap installed (if possible).
Remove the screws & & pull the horizontal firestop as far away from the wall as you can.
Determine where the one inch clearance to combustibles (CTC)is & scribe lines on the
horizontal framing members to either side of the outside if the outer pipe.
Install matching framing members (2x4? 2x6?) vertically & to the OUTSIDE of your lines,
making sure they are plumb & with 3" drywall or deck screws, fasten to the horizontal framing.
Install fiberglass insulation in the gaps between the new framing & the old.
Install small pieces if drywall or plywood covering the insulation & frame, seal any gaps with aluminum tape.
Reinstall the firestop & secure it. Seal the gap between the firestop & venting with aluminum tape.
While you have access to either side & the rear of the metal fireplace, seal any seams or holes with aluminum tape.
That includes the gas & electrical holes, and any gaps in the drywall, as well.
Do you know if there's insulation on top of the drywall above the firebox?
There should be. Kraft faced with the paper side down.
If there isn't, I would build ANOTHER deck, just above the A shaped stand-offs with
1/2" drywall laying on a band of 2x4s screwed to the existing framing, & insulate that.
If you aren't clear on ANYTHING I've stated, just ask me to clarify.
I installed as many as 20 ZC DV units a week for a couple of years,
& you want that area as sealed as possible to mitigate cold air penetration.
Good luck!

Well, I think I would do everything you recommended, if I could. However, I'm going to just try to cover both holes with two pieces of scrap gypsum glued over the existing wallboard, and flush to the edges of the firestop plate. Maybe I'll be able to get a drywall screw in their to help hold it while drying.

The long version is .....

The house I purchased was an abandoned build, built largely not to code, and with the exception of the foundation, not permitted. It was basically roofed and skinned in, with a few windows missing (framing warped and racked), vacant for four years. I had to revise every part of the build, from removing (and/or replacing) windows to properly flash them, framing, siding, HVAC, plumbing electrical, nearly everything. I acted as homeowner/builder. I'm not a trade, but I consider myself an "above average" amateur at construction (yeah, I know; that's every trade's worse nightmare). I won't go through my resume here, but I filled my knowledge gaps with lots of research. Short story long, I knew how to do this task, and would have constructed a 2x6" box within the two studs, with minimum 1" clearance on all sides, properly installed the exhaust/vent kit, insulated the sides, and essentially, done exactly what you just recommended. I negotiated this job as part of the HVAC contract. However, I can't reach that exhaust plate area unless I pull the unit out. Although the exterior cap is accessible, it's in an elevated location, and above a flight of concrete steps - not a fun place to work at all. Addressing other specifics.

• 2x6 construction.
• Insulated wall behind the gypsum wallboard.
• No insulation above the gypsum wall board on top (problem).
• You can't see it from the picture, but just FYI, there is a gypsum "wall" in the narrow void to the left of the fireplace, separating the fireplace box from that space. There were originally thoughts of putting shelving in there and maybe a door for use as a utility area, but it's just too narrow. However, the entire kick out includes insulated floors and walls, except for the ceiling.
• You convinced me. There's plenty of room for me to add another "shelf" 12" over the unit, between the upper gypsum and the fireplace unit, to slide in some insulation. I'll probably use spare CBU I have (don't have a piece of gypsum that large), to minimize the combustibles in that area. Note: The unit came with a required 10" piece of insulation (gypsum) fastened to the top of the fireplace unit, that was already crushed upon receipt. I'll replace that with a piece of CBU, then install a plywood skin above that, and over the entire fireplace surround as both structural support and to add depth. Then 1/2" CBU goes over the plywood, and overlaps the steel face of fireplace unit, to about 1" on sides, and 1-2" on top. Manufacture's instructions restricts combustibles above and to the sides, but shows non-combustibles, like marble, right down to the opening and upper eyebrow. Then I'll skin the entire face of the fireplace with 1/2" plywood, before adding 1/2" CBU and the ledgestone surround.

If I were still 30 years old and trim, I'd probably do as your advise. But I'm 64 years old and ..... ah.... "heavy set" , so I'm going to compromise. So as I said, I'm just going to try to cover the gaps around the firestop plate, insulate the top, and call it "good enough". The HVAC guys properly sealed the exterior siding, so I doubt there's air flow through there. Covering the holes on the inside will prevent any airflow into the box. So, no insulation, but at least there'll be no free airflow. I'd LOVE to fix it properly, almost enough to try pulling the unit, but 64 years of wisdom is screaming at me about going "a bridge to far".

It was bad enough correcting the shoddy workmanship of the first to contractors who built this monstrosity (i.e. first owner's problems), that PAYING for more shoddy workmanship was twice as grating. I personally rehung every door in the house, except for three, two of which were exterior double doors (they're close enough that I don't want to rip out interior/exterior trim and siding), and one which is a pocket door which is great, other than the fact it won't open. I'll probably end up tearing the wall out to resolve that one. I could tell you stories, but after about three hours, folks eyes seem to glass over (or we're drunk by then, or both). The house came out in pretty good shape. The best of it were the trades and contractors I met, who DID do great work. Good people tend to do good work. I was new to this (Northern Idaho) area, and didn't have any contacts. If I had to build again, I already know about half the contractors I'd need, guys who I could trust completely. Overall, the HVAC guys weren't that good, but they weren't bad, either. The original HVAC install was a mess (every conduit and plenum was flooded, water in them for FOUR years prior, and the 4 ton blower unit was way over spec'd), so they added and fixed a lot. They made technical errors, but came back a bunch of times to make everything right, and I appreciate that. This part, well, not so much.

Thanks for the tips and help!

 

[DAKSY]

As long as you seal it well, you should be good to go.
FWIW, I will 68 in a month & still climb into chases if need be.
I did drop 30+ lbs, & got to admit, I am a lot more agile...
Just make sure you seal around the firestop & pipe.
You install looks like it's in a bump out (ie Dog House) from
the heated envelope of the house. If that's the case,
the only heat in that area will be from that unit.
When it's not running, that metal box will be cold & you
will probably feel a draft from the bottom of the unit.
This happens when warmed air in the room enters the
top louvers of the fireplace, gets cooled by the box & drops
DOWN the cavity where a blower would move cold air UP
& out.
Hope you get it taken care of to your liking, &
Thank You for Your Service.

 

[OldSaltUSNR]

As long as you seal it well, you should be good to go.
FWIW, I will 68 in a month & still climb into chases if need be.
I did drop 30+ lbs, & got to admit, I am a lot more agile...
Just make sure you seal around the firestop & pipe.
You install looks like it's in a bump out (ie Dog House) from
the heated envelope of the house. If that's the case,
the only heat in that area will be from that unit.
When it's not running, that metal box will be cold & you
will probably feel a draft from the bottom of the unit.
This happens when warmed air in the room enters the
top louvers of the fireplace, gets cooled by the box & drops
DOWN the cavity where a blower would move cold air UP
& out.
Hope you get it taken care of to your liking, &
Thank You for Your Service.

Thanks for the weighty encouragement, lol. If I could drop 80 lbs, I'd be 30 yrs old again.

Yep, it's a bump out, off the ground outside, about 6' wide originally.

The electronic ignition won't light the pilot below about 35-40F, presumably due to condensation in the pilot light tube. I keep the pilot lit from November through March, and the little bit of heat from that seems to keep cold air moving out. So, I don't get a draft. (Of course, it cost's me about $15 in propane a month, but apparently that's start of the art, i.e. pilot for cold weather, with these electronic ignition gas fireplaces.)

Thanks again.

 

[OldSaltUSNR]

A couple more pictures, for your entertainment.

1) The firestop plate isn't even touching the wall.
2) The HVAC tech bent the plate, trying to fit it over the drywall, rather than removing drywall behind it so that it would fit flush. By the way, the bottom of the plate barely contacts the edge of the hole in the wall.
3) Since I removed the studs and am able to get in close, I can see daylight inside the hole in that wall. It's sealed outside, but there are gaps showing daylight.

We had this fireplace surround roughed in, and have been living with it for three years, until I finally got around to working on it. I had my suspicions that their may be problems. Every single thing I've removed has reaffirmed those, as in "Man, I'm glad that I pulled that off there to see what I didn't know ....".

I'm going to see if I can reach down there far enough to pull that plate back, and then I'll see if I can add something structural to either side of the tube, maybe a 1x4 or whatever will fit. Then, I'll just apply the ancient wisdom: "A little caulk and paint make the carpenter what he ain’t. "

That's not the way I do things.

 

[DAKSY]

That depression in the fire stop should fit INSIDE the hole in the sheetrock
& between the vertical framing members. Some of the gaps you see thru the
outside may in fact be light coming thru clear silicone, but seeing the rest of the cob job
you ended up trying to repair, I doubt it...

 

[OldSaltUSNR]

Sorry for the late follow -up; got busy, had some medical issues.

To wrap this up:

1. The width of the opening was only 15" wide, with an 8" pipe, and 12" W x 14" H stand off/fireblock pan. I thought of cutting and sliding a piece of concrete board (CBU) in vertically, 1" away from the pipe on either side, glued in place, and then stuffing insulation in the couple of inch void on either side. However, I couldn't see well enough to ensure that that void would be totally insulated from the pipe. Besides, I'd be doing all of that for a couple of inches of insulation; just not worth it.
2. So I decided to just seal up the opening as best I could with the pan. I cut a "U-shaped" piece of concrete board (see picture), slid that around the pipe, glued in place with construction adhesive, with a couple of screws into the studs at the top where I could reach with a drill. I added a 8" wide piece of CBU to create the square, which provided a proper 10" W by 12" base for the pan to seal against the wall. Unfortunately, I messed up by installing the CBU a half inch too far to the right, and still had to muscle the pan to fit the opening. I used Rutland high temp (500F) adhesive sealer around the edge of the pan to ensure an air tight seal.
3. Installing all of this behind the fireplace appliance with about 6" of less clearance, was a real chore. I real "swearing-like-a-sailor" chore. I literally punched the CBU screws into the CBU using a hammer turned flat sided, and then screwed the self-tapping screws using a stubby Phillips screw driver and the "muscle" of my finger tips.
4. I added a bead of latex caulk between the gypsum wallboard and the CBU, on top and sides where I could reach it.

The Rutland silicone sealer got all over everything. Hands, the plate, the back of the fireplace, the screwdriver. It was just a mess. I have a much better rear air seal now than I started with, but it's not a proper job.

I also added the shelf above the fireplace (again, using concrete board). The manufacturer's specs says combustibles are OK down to the stand-offs, which are about 6" above the unit, so I could have used plywood. However, I used as few combustibles as possible in that upper chamber anyhow. I also added a 12" x 12" plywood blocker above in the adjacent void, and stuff both with R19 insulation. I sealed the front of that "shelf" (again, see pictures) with scrap OSB.

Overall, it's air-sealed and (relatively) safe. I've done all I can without pulling, and reinstalling the unit. For all the hassle, it might have been cost less time just to pull it out, gut that knock out, start over, and do it correctly. But, it's done.

Thanks for the advice. Hope the pictures are entertaining (good for a few laughs, anyhow).