BK: How to OAK

[Ashful]

It looks like I might be finally able to add OAK's to my two BK Ashford 30's. Those who've been on this forum more than a few years already know the setup, two BK 30's pushed into walk-in fireplaces, the entry point is thru 22 inches of mud-stacked granite and red shale.

The stoves sit less than a foot off the rear wall of the fireplace, so total duct length will be very short, essentiall wall thickness plus a foot, with an elbow up into the stove's adapter. I bought a 3" OAK adapter plate, which BKVP said something like "should be fine for your short run", so it sounds like there's at least some chance I might need to up-size to 4 inch later.

The primary quesiton comes down to what size core drill to purchase for this penetration, which is obviously going to depend on the type and OD of the duct to be used, relative to a given nominal size (e.g. 3 inch or 4 inch). What type of duct is typically used in these OAK's? Given my mud-stacked stone wall construction, I'm going to want to favor something that's heavier and stainless, as we've seen too many other galvanized penetrations rot thru in the past, and the potential for shifting inside mud-stacked stone walls is higher than for modern walls with cement bedding mortars.

And then there's the connections to and exterior finishing of. Looking for some sort of rain hood that will look reasonably acceptable on exterior stone walls.

Specific duct product recommendations?

 

[begreen]

Sounds like 3" will work well. The duct size will largely determine on how restricted the air flow will be. Short runs with minimal 90º turns will work with 3". Longer runs with a few 90º turns will benefit from going up in size. Galvanized duct, aluminum flex duct are fine. Even PVC pipe will work as long as the connecting end transitions to metal to connect to the stove.

 

[Ashful]

I'm familiar with duct work that has standard sizes, and one end belled or crimped to fit into the next, whether that be HVAC duct or stove pipe. Is there no similar standard used for OAK piping?

I really want to avoid galvanized, as I've personally seen how fast it corrodes in our walls. Aiming for stainless, and preferably something with a heavier wall, if I can find something that will mate up with an exterior vent hood and interior plumbing.

If I can't find a workable stainless solution, aluminum might work.

 

[begreen]

Aluminum dryer duct would work. Given the short run, a length of 3" stainless stove pipe might also work.

 

[weee123]

Schedule 40 pvc or stainless automotive exhaust pipe would be your best bet through the wall. If your walls shift as much as you say the flex duct could potentially crush/kink. Pvc is what gets used for 90% furnace exhaust as well. If you could find stainless spiral duct that would work as well, but working commercial hvac smallest spiral duct I’ve seen is 4”

 

[xshmoox]

I work in hvac. I’d probably go either pvc. Or do a pvc sleeve and run metal ducting through it. Or you could try this stuff which may work good and last since it’s stainless and if you can make the combos work it’s gasketed since it’s meant for high efficiency exhaust venting. They do have elbows and different lengths

https://www.supplyhouse.com/Z-FLEX-2SVEPWCF0304-3-x-4-Z-Vent-Pipe-9786000-p?utm_source=google_ad&utm_medium=Shopping_HVAC&utm_campaign=Shopping_X_HVAC_X_SSC_New&utm_campaignid=22357738074&utm_adgroupid=176777929837&utm_targetid=pla-2435666339679&utm_product_id=2SVEPWCF0304&utm_matchtype=&utm_keyword=&utm_adtype=pla&utm_category=HVAC&gad_source=1&gad_campaignid=22357738074&gbraid=0AAAAAD_WAysPYh4ABryG2nDcD5EGt60yH&gclid=Cj0KCQjw8c3VBhCsARIsAA_xJ93xWEfc9uHV80YOEsrHvZ13AKG0jaSfvNF-i0jROAAB3ArYOwihDy4aAjh4EALw_wcB

 

[EbS-P]

Even PVC pipe will work as long as the connecting end transitions to metal to connect to the stove.

This was what I was thinking

 

[Ashful]

Just finishing up one of two large projects that are preceeding this one, so starting to think more about gettng the tools and materials in to make this happen. Of course, it's looking less and less like I'll get this done before running any stoves for the year, but heck... that's the way the start to most heating seasons seem to go. I also still have to clean and re-gasket the stoves, which was never done at the end of last season.

Speaking of which, didn't the prior heating season end just two weeks ago? This summer went way too fast.

PVC has a thick wall (at least sch.40), requiring a larger hole, and in the 3" size the OD is 3.5", many of the longer coring bits not even coming in that size (3.25" is more common). It's obviously also susceptible to heat, not that an OAK should be getting that hot, I guess.

The 3" stainless automotive exhaust tubing option is attactive, as I've had 3" stainless exhaust on some of my past muscle cars, and it's quite heavy and durable. But I'm wondering what elbow or flex duct might actually mate up to this cleanly? I guess I'm just used to venting systems that are designed with ID/OD and bell flare diameters that allow one pipe to mate cleanly with the next. That's obviously not going to be the case with random PVC pipe or automotive exhaust tubing.

 

[Highbeam]

PVC has a thick wall (at least sch.40), requiring a larger hole, and in the 3" size the OD is 3.5", many of the longer coring bits not even coming in that size (3.25" is more common). It's obviously also susceptible to heat, not that an OAK should be getting that hot, I guess.

The 3" stainless automotive exhaust tubing option is attactive, as I've had 3" stainless exhaust on some of my past muscle cars, and it's quite heavy and durable. But I'm wondering what elbow or flex duct might actually mate up to this cleanly? I guess I'm just used to venting systems that are designed with ID/OD and bell flare diameters that allow one pipe to mate cleanly with the next. That's obviously not going to be the case with random PVC pipe or automotive exhaust tubing.

So PVC, schedule 40, is sized based on OD so the wall thickness only effects the inside diameter. Same size hole.

I like the SS exhaust pipe idea the best and I would recommend the 4" because going back in to go from 3 to 4 would be difficult. I upsized my 3" OAK to 4" partly because it was so much easier to find compatible fittings, pipe, and even the termination hoods from the HVAC world.

I would plan on core drilling through such a stone wall at least 1/2" oversize so that you can correct slope issues, you want it to slope away from the stove, and if you get a weird loose stone in the hole you have some room to work. You'll need to seal the penetration anyway.

I expect you will want a piece of flex pipe between the stove and the rigid pipe anyway and the dryer vent section of a hardware store will have the parts.

 

[GG Woody]

Some insulation attached to the outside of the pipe would be preferred in our HVAC best practices. Foil backed duct insulation is made for that purpose, but any insulation would help. Engineers on commercial HVAC jobs here require it, and I believe it is in the residential building code as well. The insulation will help with the pipe degrading by electrolysis as well as helping with condensation, picture a can of cold beverage (cold air) in a warm environment.

 

[Ashful]

So PVC, schedule 40, is sized based on OD so the wall thickness only effects the inside diameter. Same size hole.

While is true that scheduled PVC pipe (e.g. 40 and 80) are based on OD (3.5" for "3-inch"), I was referring to the PVC products folks actually face in a store, namely DWV versus S&D. Or to put it more clearly:

3 inch S&D OD = 3.25 inches
3 inch sch.40 OD = 3.50 inches
3 inch sch.80 OD = 3.50 inches

But no matter. I like their resistance to corrosion, but I don't think either is a great choice for installing in the back wall of a 300 year old fireplace, for several reasons.

I like the SS exhaust pipe idea the best and I would recommend the 4" because going back in to go from 3 to 4 would be difficult. I upsized my 3" OAK to 4" partly because it was so much easier to find compatible fittings, pipe, and even the termination hoods from the HVAC world.

Yep... that's the present debate. I'll have to un-box the 3 inch OAK adapter I bought for the Ashford 30. Does anyone have a photo of the 4 inch one, or can they get some basic dimensions?

I'm not worried that much about termination hoods, I think the difficulty of finding a suitable hood that mates up with automotive exhaust in either size is going to be a bit of a challenge, silicone will presumably be involved.

Probably looking at something like this, sandblasted and painted a suitable brown or gray:

https://www.roofingdirect.com/shop/rdp-aluminum-hooded-wall-vent-with-screen-no-damper/?attribute_size=3+in.&gad_source=1&gad_campaignid=24003988202&gbraid=0AAAAACgs7s5LFqKiknDGymmaiNR45ILlO

I would plan on core drilling through such a stone wall at least 1/2" oversize so that you can correct slope issues, you want it to slope away from the stove, and if you get a weird loose stone in the hole you have some room to work. You'll need to seal the penetration anyway.

Agreed.

I expect you will want a piece of flex pipe between the stove and the rigid pipe anyway and the dryer vent section of a hardware store will have the parts.

Agreed. Although what's the common method of affixing incompatible pipe diameters, in this application? I guess air tightness is of low concern, other than leaking cold air or summer insects into the house.

 

[weee123]

The dryer vent/flex duct will slide right over which ever pipe you use as long as it’s the same diameter. The crimped end of an adjustable elbow will slide right into any pipe that is the same diameter, and you can crimp it tighter if necessary to make it happen. If you’re using the dryer vent I don’t see why you would even need an elbow at all.

Also make sure you don’t use dissimilar metals as they will eventually corrode due to electrolysis. If you do, use a healthy amount of silicone so the metals don’t touch. I’m partial to Solar Seal when it comes to sealing outside envelope of a building against air and water intrusion.

 

[brenndatomu]

I'd personally go with a 4" hole through the wall, and use stainless stovepipe...lots of adapters available down to 3" then...first thing that comes to mind is a 3-4" adapter for the old single wall gas furnace vent pipe...you'd have to decide if an increaser or decreaser works better.

I don't envy you going through a 22" wall...we just had to bore a 10" hole through concrete at work...it was a new and an old wall poured against each other...took 2 trips in with a 16" deep core bit on a vacuum mounted rig, 6' off the floor...fun.

Then I just finished a 10" hole through the basement wall at home, that was just block, but it was 5' off the floor, and had to hold the 44lb rig by hand...I could only go a couple minutes between breaks, and less at the end...but it went fine and was done in an hour ish...still gotta finish putting things back together on that one.