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CallMeVilla 04-12-2014 02:30 PM

Tankless Water Heater
In a tight situation ... The owner wants to put a tankless water heater on the exterior wall. The windows are within 3 feet of the unit, although the exhaust conduit will carry any off gasses above the roof line.

Advice on the best orientation?

Wuzzat? 04-12-2014 02:42 PM


Originally Posted by CallMeVilla (Post 103323)
Advice on the best orientation?

"Depending on the orientation that is right for your home, your tankless water heater can either vent horizontally through an exterior wall or vertically through your roof. It is very important you realize that you will not be able to use your existing venting with your new tankless system. You will need to use venting approved by the manufacturer.

You also want someone who knows all of the national and local codes that apply."

So I guess you should post a link to the make/model that you are using, and code excerpts. Each of us may get something different from this info.

CallMeVilla 04-12-2014 07:21 PM

1 Attachment(s)
Don't know the details yet ... just anticipating the location issues. Most exterior tankless models do not even have vertical venting. They just dump the gasses horizontally in the front of the unit. My concern is clearance requirements between the face of the unit and the nearby window. (see attached picture)

What I was looking for was anyone who had dealt with that problem when installing a tankless.

Wuzzat? 04-12-2014 08:03 PM

See page 8, second row in the table
Also pg. 9., plus I've seen 5' or 6' numbers. With all the caveats in this manual many customers may opt out of installing these things.

Probably bigger input BTU/hr units need more space.

You might try pulling up another manual picked at random from the Web. If the numbers are close you're in good shape. If not, if the numbers are all over the map then maybe U.L. has the final word on this.

Hope this helps.

havasu 04-13-2014 09:10 AM

1 Attachment(s)
Here is how I installed my TWH. This was done by code and passed all inspections.

Wuzzat? 04-13-2014 11:50 AM


Originally Posted by havasu (Post 103343)
Here is how I installed my TWH. This was done by code and passed all inspections.

Any openable windows nearby?

If you can post a link to your manual we all can see what differences there are between the link I posted and yours. These things may have a range of 50,000 to 500,000 BTUh so there may be other differences besides the size of the gas supply lines.

I'd think even the hot water line would need protection against freezing in some places if there is a long time between the demands for hot water but my link only mentioned cold water line protection.

CallMeVilla 04-13-2014 12:22 PM

Hope to have the unit specs next week. There is an operable window nearby ... but it can be secured to comply with inoperable requirements. Will take pics of the actual site and share as we get to that part of the total remodel.

Since this is Southern CA (Neal, that would mean "California") we don't have freezing problems. I anticipate vent piping to divert off gasses away from the wall and the small overhang (only 3").

THANKS for all the really excellent input from Wuzzat and Havasu

nealtw 04-13-2014 01:42 PM

How did I get into this, I just thought CA was short for ca ca.

havasu 04-13-2014 03:13 PM

The Navien TWH has a built in freeze protection, where it will begin to cycle when the temperature dips to just above and at freezing temps.

Attached below is the PDF spec. sheet for the Navien NR-240 TWH.

Wuzzat? 04-13-2014 05:46 PM

Thanks. Pg. 35 has some clearances.
these suckers are heavy. . .

Regarding "the time to burn a child" table on pg. 66, I've heard that 42C will never burn an adult with normal blood circulation so if you don't have kids you can crank up the temp a bit.

At 11 GPM and 200,000 BTUH you only get a 37 F water temp rise but with a bathtub filling at 6 GPM you'd get a 67 F rise. I guess this is enough.

I don't have one of these but the numbers are telling me that as the temperature of the incoming water gets colder in winter you'll need to fill the bathtub more slowly if you want the same bath temp.

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