OK to hang boiler on pressure treated plywood?

Bill751

I am about to mount a wall hung mod con boiler in my basement. The existing concrete wall has a significant slope outward as it rises. That is how it was formed and poured. To make everything plumb and square I've done some framing with pressure treated 2x4's and screwed untreated 3/4" plywood to that. This was last winter before I left town for work. I never did get around to installing the boiler. Fast forward to now when I am about to restart the project and I see that my plywood has mold on the surface while the treated 2x'4's do not. The house is about 160 years old and gets damp in the basement at various times. so I suspect the mold to continue to be a potential issue with untreated wood. My first thought was to use pressure treated plywood but I wanted to be sure that it would not cause any issues with the boiler/ near boiler piping.

I read that pressure treated wood is extremely corrosive to steel and aluminum. what I read suggested there would be no problem as long as a barrier was placed between the wood and the metal. What do the heating professionals say?

1. Is it ok to mount the boiler on pressure treated plywood?
2. If so, what would be a good barrier to place between any contact points from the boiler to plywood?
3. Are there any potential issues with off gassing from the treated plywood to be concerned about with the boiler or near boiler copper piping?
4. anything else I should know about, consider doing or using?

any help would be greatly appreciated

kcopp

Beyond the nasty plywood and reactions between the PT and the boiler... how about having a boiler w/ sensitive electronics being installed in a damp basement? Is there a better drier place?

Bill751

kcopp said:

Beyond the nasty plywood and reactions between the PT and the boiler... how about having a boiler w/ sensitive electronics being installed in a damp basement? Is there a better drier place?

I certainly would like to install it somewhere else, however it's not really feasible at this time. I've not used a hygrometer down there so I don't know how much moister is in the air at times. I will say that I was really surprised to see the mold on the plywood, or at least so fast. The 160 year old first floor joist and subfloor are not covered in mold. so why the plywood molded so fast i do not know.

I could monitor the moister and run a dehumidifier down there to keep it within acceptable levels for the boiler. it's not horrifically damp down there, I've been in much damper basements that's for sure.

So it would be safe to say that professionals would warn against installing over treated plywood?

STEVEusaPA

Well any treated wood would/could outgas. I wonder if you should just take the plywood off, clean, replace, and prime it on all sides with Kilz, then paint it. Make sure it doesn't touch the floor and leave an air space at the top.

kcopp

I usually paint all the wood w/ a good porch/ floor enamel.

Brewbeer

Bill751 said:

The 160 year old first floor joist and subfloor are not covered in mold. so why the plywood molded so fast i do not know.

The old wood is likely old growth wood, which is more resistant to mold than the modern plywood that had the mold. Definitely run a dehumidifier in warm and humid conditions.

Bill751

STEVEusaPA said:

Well any treated wood would/could outgas. I wonder if you should just take the plywood off, clean, replace, and prime it on all sides with Kilz, then paint it. Make sure it doesn't touch the floor and leave an air space at the top.

Painting had briefly crossed my mind but for whatever reason I really didn't give it much more thought once I started considering using treated wood. I do think painting sounds like a good solution. I'll probably just buy some new plywood and go that route. Thank you for suggestion

Gordy

NO, if not for the sake of anything else the boiler cabinet. That's why you use special triple coated screws for pt wood. Even then they get ate up after years.

Couple the pt with a humid environment where the wood will never lose some of the treatment like in outdoor applications.

hot_rod

I've been using Yellawood treated lumber it is approved for use in gardens and exposed framing. It's not as toxic as the earlier treated lumber. Standard galvanized fasteners, or stainless work fine. Scraps can be burned or put in landfills.

Bill751

kcopp said:

I usually paint all the wood w/ a good porch/ floor enamel.

I think this would be a good solution to the problem. Nothing else is covered in mold. so once painted plywood should be fine. I'm going to start monitoring the basement humidity with a wireless indoor/outdoor thermometer/hygrometer setup. outdoor transmitter placed in the basement of course. I'll have to do some quick research on the allowable levels for the boiler and go from there. Thank you for the suggestions and pointing out concerns

BobC

My cellar gets very humid in the summer, for years I used a dehumidifier but as electric rates went up (now 19.5 cents per kwh) I looked for an alternative. I installed a 4-1/2" muffin fan into a pane of a cellar window (now a lucite pane) - problem solved.

I cover the fan in the late fall and remove that cover in the late spring.

Bob

Gordy

hot rod said:

I've been using Yellawood treated lumber it is approved for use in gardens and exposed framing. It's not as toxic as the earlier treated lumber. Standard galvanized fasteners, or stainless work fine. Scraps can be burned or put in landfills.

It's all safe until 10 years later.......

JUGHNE

Most lumber we get today is not dried very well. Could it be that your plywood was of high moisture content when it went into the basement. If you could leave a piece out in the sun & wind for a while it may dry out enough to not have a mold issue.
Of course it may warp like hell.

Bill751

BobC said:

My cellar gets very humid in the summer, for years I used a dehumidifier but as electric rates went up (now 19.5 cents per kwh) I looked for an alternative. I installed a 4-1/2" muffin fan into a pane of a cellar window (now a lucite pane) - problem solved.

I cover the fan in the late fall and remove that cover in the late spring.

Bob

Exactly the reason I haven't ran a dehumidifier down there yet. At one point I had one running in another area and was surprised how much it cost a month. I used a Kill A Watt meter to confirm the usage. I like the fan idea and will definitely look to go that route with the new boiler being down there. Thanks for the suggestion

Bill751

JUGHNE said:

Most lumber we get today is not dried very well. Could it be that your plywood was of high moisture content when it went into the basement. If you could leave a piece out in the sun & wind for a while it may dry out enough to not have a mold issue.
Of course it may warp like hell.

It did not seem overly damp when I bought it/ cut it. but there could have been a little in it. It is a little damp down there so I think I'll just go with the painting idea to be sure it doesn't happen again. Thanks

Bill751

Thanks Everyone for the replies.

ChrisJ

Gordy said:

hot rod said:

I've been using Yellawood treated lumber it is approved for use in gardens and exposed framing. It's not as toxic as the earlier treated lumber. Standard galvanized fasteners, or stainless work fine. Scraps can be burned or put in landfills.

It's all safe until 10 years later.......

Good old school pressure treated wood was never considered "safe". But it was good for it's intended purpose.

I've heard the modern stuff is safe, but isn't very good as far as lasting.

Gordy

Chromium Copper Arsenate (CCA)was considered safer when it first hit the market Back in the 30s. There were never any real warnings on its hazards until early 80's.

Yella Lumber says you can burn, but only in an incinerator.

https://en.wikipedia.org/wiki/Chromated_copper_arsenate