Any idea what it would take to install a hot water heater outside my house?
No idea really, I haven't looked at the applicable code requirements. But here are some considerations:
- Putting a gas water heater outside the building envelope would eliminate or reduce concerns about indoor air quality that these appliances can sometimes cause. No potential for CO poisoning due to negative air pressure in the home, etc.
-Building an outside enclosure for the water heater could give you flexibility to make the space big enough to get a less expensive or more efficient water heater (plenty of insulation, or wrap it yourself with more, etc) . Also, the extra space and access would be an ideal opportunity to put in a PEX "home run" style manifold for the outgoing hot lines to each point of use in your home. A small 3/8" line generally provides all the flow needed by a typical sink or dishwasher, and 1/2" is enough for a shower. The hot water will arrive at the point of use much more quickly through a small, direct line from the WH than it would through a 3/4" main pipe covers most of the distance to the point of use (which is typically how non-PEX systems are laid out).
- Energy concerns: An outside cabinet will transfer less lost heat from the WH to your home--good in the summer, bad in the winter. Also, a "conventional" gas WH in the home uses inside air for combustion and sends a lot of that heated/cooled air from the house up the stack, which costs money. And, the flue/vent hood continually lets air out of the house even when the WH isn't running. If the water heater is outside, it isn't continually leaking your home's air to the outside world. Now, some of these concerns can be reduced by use of a newer-style sealed-combustion WH (they take their combustion air from outside). These sealed combustion WH are considerably more expensive and have more things to go wrong.
- An outside location (with floor sloped to the yard) totally eliminates the big potential for damage to your house when the water heater rusts out. It also could make installation and servicing a lot easier than the a location in a small interior space (you could conceivably make the wall panels removable after detaching a few screws attached to corner posts).
- Cost could vary a LOT depending on the situation (distance from existing lines, steps needed to assure the in and out lines never freeze, aesthetic concerns (need to match the brick of the house? $$$! Happy with some Hardiboard painted to match or complement the house? = cheap).
- Outside cabinet ventilation: If using a conventional gas water heater, you'd need need open louvers at the top and bottom of the cabinet to allow combustion air in. This will obviously mean that the inside of the cabinet will be pretty close to the temperature of the air outside your house, which might complicate the task of assuring the water lines don't freeze, and might make the WH work harder in cold weather. If you used a sealed-combustion WH, >theoretically< the cabinet could be sealed and the temps inside could be kept higher (using an uninsulated shared wall with the house and/or waste heat from the water heater, etc). I do
NOT know if this is allowed by code or even a good/safe idea (is venting required to assure any vented/leaked gas can get out before reaching combustible concentrations, etc)
If you go the tankless route, installing a WH outside can be relatively simple. There are tankless units designed to hang on the outside of an exterior wall, no need to build an enclosure, etc. You'd still need to assure the lines to the WH don't freeze, which could be tough in some places. But a tankless heater has it's own issues (cost, complexity/reliability, possible need to upgrade the gas and esp electrical service). Also, in places subject to possible loss of water/electrical/gas service, having 50 gallons of potable and (initially) hot water constantly available in a home can be a very handy thing.
So, definitely consult with somebody knowledgeable before pressing ahead. I have no expertise in this.
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