Where to install tankless hot water heater

scrapndoodleJanuary 4, 2010

Having weighed various pros and cons, I am leaning toward replacing my tanked water heater with a gas tankless if it is feasible.

We would have a professional installation, but I am trying to get an idea of site-ing issues and potential retrofit costs.

We have a townhouse, on a small lot. Our current tanked water heater is in a room at the back of our house (brick walls). The brick backs up to a wooden shed at the back of our property line. The shed is a sturdy structure with a roof. Our current water heater is vented through the chimney flue. We can't vent a new tankless system through the side wall of the "water heater room" because of the location of our neighbor's house.

I was wondering if any of the following would be possible:

1). Mount on interior of back brick wall. Water heater would "direct vent" into the shed. If this is allowable, how much clearance is needed from vent to roof of shed, from side walls of shed, etc.

2). Mount on exterior of back brick wall, inside of the shed. This is assuming that venting in the shed is not an issue (from #1).

3). Mount on exterior side wall of house. (the side wall opposite the one where the current "water heater room" is). This location would be near the gas and water meters.

An additional concern I have with #2 and #3 is pipe freezing. I have heard that exterior machines have mechanisms to prevent freezing ... but what if the power goes out? I am in Virginia near Washington, DC.

Thanks in advance for your thoughts!

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You want to do a few things with locating your heater:

1. locate it so that it can be vented in an approved way (you can't locate the vent too close to windows, doors, etc.)

2. Locate it so that the vent run is short as possible (a few feet is good) if that's not possible, consider a condensing unit that vents with PVC. Stainless Steel venting is VERY expensive. A condensing unit adds several hundred dollars but can be cheaper than a long run of SS vent

3. Locate the heater close to where the water is being used. I was able to locate my heater 20' closer to the bathroom than it was.

You can't vent the tankless through an existing flue and you sure can't vent it into a shed.

Why can't you vent it to the sidewall? How close is the neighbor's house?

You want to mount the unit inside unless you have really mild winters. For mild winter areas they have external installed units. Both interior and exterior have freeze protection, but that should be a fallback protection system.

Here is a link that might be useful: See Pg 12 for venting locations

    Bookmark   January 5, 2010 at 2:02PM
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Thanks for your thoughts. The chart is very helpful. It sounds like our only option is through the wall by our neighbor's house. I will have to look further at this. Our house is not attached, but there is only a 2-3 foot wide alley. It might work if mounted high enough and if we used a condensing model so that the flue gas was not as hot. It would not be venting right toward their house but toward their fence (house starting a couple feet away). Of course, the other option is to keep our tanked model.

    Bookmark   January 5, 2010 at 8:12PM
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The vent points down. You don't have to worry about hot gases as much as CO. You can't vent it where it would would be drawn into a window or door that was open. Other than that, I don't think it's the problem you believe it to be. You basically have to be 4' from a below or to the side of any window or door or 4' from air intake on another building. Unless there's a door or window right next to the outlet, you don't have a problem. The flue gases aren't that hot when they exit.

    Bookmark   January 5, 2010 at 10:39PM
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