Thread: Tankless Water Heater in Stud Wall

This is a Rinnai unit. Besides the fact that it is installed closer than 6" to combustibles on the side walls, there is now no space to add insulation behind this unit.

I have the installation instructions to cover the side walls, but could use something better than what I've come up with regarding the back of the unit not being insulated.

Ideas?

Aaron

Similar Threads:

• ABS Flue Pipe on LP Water Heater
• Tankless water heater comment
• Water heater Question
• Staining on exterior wall near A/C
• Reverse plumbing to water heater

Aaron,

Tankless units not common here. But a question I would have. What happens when the unit develops a small leak? Maybe one that is not large enough to leak through the wall cavity. Somehow putting the unit inside a wall (concealed) does not make sense to me. If it begins to leak I'd like to know about it right away. Nothing wrong with the common sense approach.

Originally Posted by Eric Barker

Aaron,

Tankless units not common here. But a question I would have. What happens when the unit develops a small leak? Maybe one that is not large enough to leak through the wall cavity. Somehow putting the unit inside a wall (concealed) does not make sense to me. If it begins to leak I'd like to know about it right away. Nothing wrong with the common sense approach.

Eric:

And they all leak, eventually.

My biggest concern is that the back of the unit will condense moisture which will grow mold on the drywall adjacent to it. Additionally, there will be that area of the wall which is not insulated. And did I mention that this is the north wall?

Aaron

Aaron,

I have only run across the Rinnai 3 times recently. The way you have it pictured, where the removable cover is on the exterior is how I've seen them every time, with no insulation on the garage side (a non-air conditioned side).

The trouble I have encountered two of the three times is that the upstairs unit needed a cross-over link to be supplied with "Hot" water-- otherwise the water coming out of the supply fixtures was warm only.

I've been doing one area of Irving (Los Colinas area) where it looks like sunny South Florida with the tile roofs, stucco and designs going up... All of these have the Rinnai tankless heater systems.

rr

Originally Posted by Aaron Miller

Eric:
My biggest concern is that the back of the unit will condense moisture which will grow mold on the drywall adjacent to it. Additionally, there will be that area of the wall which is not insulated.
Aaron

Aaron,

Your statement would work for my client. If the install is on the plans without proper clearance I would note that as well.

Originally Posted by Richard Rushing

Aaron,

I have only run across the Rinnai 3 times recently. The way you have it pictured, where the removable cover is on the exterior is how I've seen them every time, with no insulation on the garage side (a non-air conditioned side).

The trouble I have encountered two of the three times is that the upstairs unit needed a cross-over link to be supplied with "Hot" water-- otherwise the water coming out of the supply fixtures was warm only.

I've been doing one area of Irving (Los Colinas area) where it looks like sunny South Florida with the tile roofs, stucco and designs going up... All of these have the Rinnai tankless heater systems.

rr

Richard:

This one is in a bedroom.

Most I have seen are in garage walls and 2X6 at that. The exception is the area you are discussing where I have been ten times this year. Hovnanian has not a clue about many things. . .

Aaron

What part of Texas are you in?

Out of 10 cities listed in Texas in Table D101, Degree Day Design Temperatures for Cities in the United States, only Houston is listed at 32 degrees or higher (Houston is listed at 32 degrees).

If you are above the Houston line, that entire water heater and all of its plumbing lines (for the entire house) are required to be within the insulated thermal envelope of the house.

Thus, your concern regarding insulation is a bigger one than I suspect you were thinking it was.

Are we looking at the access door, or is that facing the exterior?

Originally Posted by Aaron Miller

This is a Rinnai unit. Besides the fact that it is installed closer than 6" to combustibles on the side walls, there is now no space to add insulation behind this unit.

I have the installation instructions to cover the side walls, but could use something better than what I've come up with regarding the back of the unit not being insulated.

Ideas?

Aaron

I tried to find Rinnai instructions online (I see you have some) but in reading about some other brands, they mention a condensate trap in the flue that should drain to a cond. line. Is the same true for the Rinnai? And would that take care of any moisture (potential?) on the back of the unit?

The post about the plumbing being in an outside wall is very interesting. I'm sorry that I just now thought of that. These things are so common around here; I've inspected several of these units.
Bruce

Originally Posted by Jerry Peck

What part of Texas are you in?

Out of 10 cities listed in Texas in Table D101, Degree Day Design Temperatures for Cities in the United States, only Houston is listed at 32 degrees or higher (Houston is listed at 32 degrees).

If you are above the Houston line, that entire water heater and all of its plumbing lines (for the entire house) are required to be within the insulated thermal envelope of the house.

Thus, your concern regarding insulation is a bigger one than I suspect you were thinking it was.

Are we looking at the access door, or is that facing the exterior?

JP:

I'm w-a-y north of Houston, thankfully . . .

We are looking at the back of the unit. All hell would have broken loose if they had faced the access door into the bedroom . . .

Tell me about the requirement you mentioned.

Thanks,

Aaron

Originally Posted by JB Thompson

I tried to find Rinnai instructions online (I see you have some) but in reading about some other brands, they mention a condensate trap in the flue that should drain to a cond. line. Is the same true for the Rinnai? And would that take care of any moisture (potential?) on the back of the unit?

The post about the plumbing being in an outside wall is very interesting. I'm sorry that I just now thought of that. These things are so common around here; I've inspected several of these units.
Bruce

JB:

The moisture I'm concerned about would condense on the back of the unit due to the temperature differences between the interior and exterior of the house. On the north wall that can easily be a considerable differenc in the winter. In the middle of August in Dallas that can often be a 40-degree difference.

Thanks,

Aaron

Aaron, try IRC 2003
P2603.6 Freezing. In localities having a winter design temperature of 32 degrees F or lower as shown in table R301.2(1) of this code, a water, soil or wast pipe shall not be installed outside of a building, in exterior walls, in attics or crawl spaces, or any other place subjected to freezing temperature unless adequate provision is made to protect it from freezing by insulation or heat or both...
Jim

Originally Posted by Jim Luttrall

Aaron, try IRC 2003
P2603.6 Freezing. In localities having a winter design temperature of 32 degrees F or lower as shown in table R301.2(1) of this code, a water, soil or wast pipe shall not be installed outside of a building, in exterior walls, in attics or crawl spaces, or any other place subjected to freezing temperature unless adequate provision is made to protect it from freezing by insulation or heat or both...
Jim

Jim:

OK, but if the manufacturer designs the unit for and allows its installation at an exterior location, then the unit itself is allowed to be there. The plumbing, which is actually below the unit, is able to be insulated by pipe wrap and batt or other wall cavity insulation. True?

Aaron

Originally Posted by Aaron Miller

JB:

The moisture I'm concerned about would condense on the back of the unit due to the temperature differences between the interior and exterior of the house. On the north wall that can easily be a considerable differenc in the winter. In the middle of August in Dallas that can often be a 40-degree difference.

Thanks,

Aaron

All of the ones I've inspected were against a garage wall. Do the instructions forbid it elsewhere? Just curious.

My neighbor has a Rinnai on an exterior wall in their master bathroom. I'm going to go ask them if I can snoop around and see if there is any evidence of mold, etc....

B

Originally Posted by JB Thompson

All of the ones I've inspected were against a garage wall. Do the instructions forbid it elsewhere? Just curious.

My neighbor has a Rinnai on an exterior wall in their master bathroom. I'm going to go ask them if I can snoop around and see if there is any evidence of mold, etc....

B

JB:

Let me know what you discover . . .

Aaron

OK, but if the manufacturer designs the unit for and allows its installation at an exterior location, then the unit itself is allowed to be there. The plumbing, which is actually below the unit, is able to be insulated by pipe wrap and batt or other wall cavity insulation. True?

That would be my take on it. On the few I have seen in existing construction, there have been some warning labels warning about freezing conditions, I would think close scrutiny of the installation instructions would be warranted. Different models may be needed for colder climates.

Some info from various manufacturers:

Do not disconnect the electrical supply if the ambient temperature will drop below
freezing. The Freeze Prevention System only works if the unit has electrical power. The
warranty will not be covered if the heat exchanger is damaged due to freezing. Refer to
the section on the Freeze Prevention System on p. 26 for more information.

FREEZE PROTECTION SYSTEM

• This unit comes equipped with heating blocks to prevent freezing which can damage the heat
exchanger. The T-K3 also ignites automatically, without the water flow, to prevent freezing
the heat exchanger as well.

• For this freeze prevention system to operate, there has to be electrical power to the unit.
Damage to the heat exchanger caused by freezing temperatures due to power loss is not
covered under the warranty.

• The freeze protection system will activate when the temperature drops below 36.5°F (2.5°C)
and is rated to protect the unit down to -22°F (-30°C) in a wind-free environment.

• If you install the water heater in an area where the water heater is subject to temperatures
(including wind chill) below -22ºF (-30ºC), this will void the warranty and Takagi will not be
responsible for any damage to the heat exchanger as a result of freezing.

• In any areas subject to freezing temperatures, Takagi requires the use of its back flow vent
damper (Part No. TK-TV03) to minimize the amount of cold air entering through the exhaust
venting when the water heater is off.

• If you will not be using your heater for a long period of time or if the temperatures (including
the wind chill) will drop below -22ºF (-30ºC):

1. Drain the unit of water. Refer to p. 28.

2. Turn off your heater.
This will keep your unit from freezing and being damaged.

CAUTION: Only pipes within the water heater are protected by the freeze protection
system. Any water pipes (hot or cold) located outside the unit will not be protected.
Properly protect and insulate these pipes from freezing.

Some of the units specified not to be installed except in mild climates or not to be installed on a northern exposure exposed to prevailing winds, etc.

Big reason to have the manuf. instructions on site.
Jim

All Rinnai units have freeze protection. You can register and download an install manual at their website. All the tankless gas are in one manual so its helpful. If you have trouble I can e-mail you one also. I have a lot of experience with the gas tankless and the biggest problem is incorrect installation tecniques.

Those freese protection systems aren't perfect.

I had a bay of 3 commercial Norritz tankless heaters. In them the freeze protection is just a few elements touching the pipes of the heat exchanger. Something failed in all three of them, but I can't say what went first. The pipes of the heat exchanger were split from freezing, and the porcelain of the heating elements had shattered. Did the elements break, allowing the pipes to freeze? Or did the pipes freeze, burst, thaw, then spray cold water on the hot elements, shattering them? Anyways, we ended up replacing 3 heat exchangers and 9 heating elements. *probably* had something to do with the fact that these were installed on poles on the roof of a building, with no barrier on any sides against the elements.

I have been seeing more new homes with the units on the exterior wall. Around here the water pipes just have the foam pipe wrap on them. Had a re-inspect a home today that the unit was on the exterior wall and the pipes insulation was not intact since it was installed in 04.
It's the pipe wrap that is slit down it's length and has adhesive strip for sticking the sides together. I like the ones that have the programmable thermostats installed inside the home.