Thread: Tankless Mold Factory

I am seeing a lot of these installations lately. Tankless water heaters installed in exterior walls with no possibility of insulating behind them. The back of the cabinet in this photo will be in direct contact with the drywall once it is installed.

So then, a metal cabinet in unconditioned air abutting drywall in conditioned air equals what?

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Being installed like that will affect the insulation value. But I don't see, as your title suggest, that it will cause mold to form.

Do you have more pictures of this tankless unit install? I never seen them installed inside the wall before. Is it a gas tankless or electric? The manufactures of the gas units state they state the required clearance of the heater is 12" from the top 2" to either side, and 4" from the front.

They recommend 8" to the sides to help with inspection and maintenance and 24" to the front of the unit.

• If possible, leave 8" or more on either
side of the unit to facilitate inspection.
• If possible, leave 24" or more in front of
the unit to facilitate maintenance
and service if necessary.
• If possible, leave 3" or more above and
below the vent pipe to facilitate inspection
and repair if necessary

Originally Posted by Rick Cantrell

But I don't see, as your title suggest, that it will cause mold to form.

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Good Morning Rick,

I think Mr. Miller is thinking of Condensation forming on the metal cabinet being a moisture source coupled with the drywall as a food source.
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Originally Posted by Billy Stephens

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Good Morning Rick,

I think Mr. Miller is thinking of Condensation forming on the metal cabinet being a moisture source coupled with the drywall as a food source.
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BS: "Mr. Miller", now that is rich. You are correct, and so is RH. The clearances have not been met in most directions. Typical Texas builder shenanigans.

Maybe I'm missing something here.
Condensation collects on a surface that is at or below the dew point.
Being that is a Water Heater, I don't see it (the metal surface of the WH Tank) going below the dew point. Even if it were to, it at some point in time it will heat up.
So what am I missing?

Originally Posted by A.D. Miller

BS: "Mr. Miller", now that is rich.

Yeah My Initials aren't BS for Nothing.

Originally Posted by Rick Cantrell

Maybe I'm missing something here.
Condensation collects on a surface that is at or below the dew point.
\.
Being that is a Water Heater, I don't see it (the metal surface of the WH Tank) going below the dew point.
.
Even if it were to, it at some point in time it will heat up.
.
So what am I missing?

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On demand WH likely will not operate over night.

Metal Cabinet Surface cools ( more so on the Exposed Wall Side.)

Cabinet Heats ( through use or Rising exterior temperature an evaporates condensation and is trapped inside the wall.
*but I've been Wrong before.
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Originally Posted by A.D. Miller

I am seeing a lot of these installations lately. Tankless water heaters installed in exterior walls with no possibility of insulating behind them. The back of the cabinet in this photo will be in direct contact with the drywall once it is installed.

So then, a metal cabinet in unconditioned air abutting drywall in conditioned air equals what?

I see them many times installed outside the home with the back of the unit either touching or within fractions of an inch from the interior wall to the backside. They don't even have room to get insulation between it and the drywall. I have also seen them installed outside and they have a slight bump out in the brick to hold them out a bit and they put a small sheet of foam isul behind them. You are right about the cabinet sweeting and dampning the drywall which obviously leaves it open for mold growth. I have not seen any results over an extended period of time but one would think you are correct.

Originally Posted by Ted Menelly

I see them many times installed outside the home with the back of the unit either touching or within fractions of an inch from the interior wall to the backside. They don't even have room to get insulation between it and the drywall. I have also seen them installed outside and they have a slight bump out in the brick to hold them out a bit and they put a small sheet of foam isul behind them. You are right about the cabinet sweeting and dampning the drywall which obviously leaves it open for mold growth. I have not seen any results over an extended period of time but one would think you are correct.

TM: It is only a matter of time. If you are one of those with a ray gun, try taking a shot of the drywall at the back of one of these and see what you come up with.

On demand WH likely will not operate over night.

Metal Cabinet Surface cools ( more so on the Exposed Wall Side.)

Cabinet Heats ( through use or Rising exterior temperature an evaporates condensation and is trapped inside the wall.

BS: all sounds right to me.

Originally Posted by A.D. Miller

TM: It is only a matter of time. If you are one of those with a ray gun, try taking a shot of the drywall at the back of one of these and see what you come up with.

No, no ray gun here. I do not want to be in a position where I did not take a picture of a square foot of wall some place and hold it in file just incase someone tears a wall appart a year later and finds that area I did not take a picture of and who knows what that fee will be. Everyones idea that the ray guns have their own contract behind them and six page disclaimer about not seeing somethings and some things they think they see may not come up with nothing when someone tears the wall appart after your findings and now you have to pay for all the repairs even though you have been thinking your contract and disclaimers covered your sorry ray gun weilding butt. No, no ray gun for me.

However.....shhhhhhhhhhhhhh....I have exray vision but don't let it get around......I don't want to pay for something someday because I did not have a contract signed and a disclaimer about my xray vision missing something.

Thanks Billy
"On demand WH likely will not operate over night.
Metal Cabinet Surface cools ( more so on the Exposed Wall Side.)
Cabinet Heats ( through use or Rising exterior temperature an evaporates condensation and is trapped inside the wall."

I understand the concept.

I just don't think it will cool down to the dew point and have enough condensation to cause mold.
If it does, then I would think that there are 100s of thousands of electric panel enclosures that would have mold all around them.
Can it happen, it's possible.
Is it likely to happen, I don't think so.
But like you said " I been wrong before"

ad,
looks like the termites ate a good piece of those studs? 25% on bearing partitions or exterior walls and 40% on non-bearing walls.

Originally Posted by brian schmitt

ad,
looks like the termites ate a good piece of those studs? 25% on bearing partitions or exterior walls and 40% on non-bearing walls.

BS: New, finger-joint studs. They all look like crap, fall apart at the joints, scare hell out of the home buyers . . .

ad,
i was referring to the depth of the notch on the finger food studs! lineset or gas line or whatever that is they notched for.

Originally Posted by Rick Cantrell

Thanks Billy
"On demand WH likely will not operate over night.
Metal Cabinet Surface cools ( more so on the Exposed Wall Side.)
Cabinet Heats ( through use or Rising exterior temperature an evaporates condensation and is trapped inside the wall."

I understand the concept.

I just don't think it will cool down to the dew point and have enough condensation to cause mold.
If it does, then I would think that there are 100s of thousands of electric panel enclosures that would have mold all around them.

I think it could happen, cold water and even colder propane flowing through metal pipes, not the same as warm electrons flowing through wiring.

John
My thought is; whenever water or propane are flowing, the unit will be heating.

Run out of propane, break the exhaust fan, heat the well pressure tank with a tiger torch, it could grow mould (mold).