I will be building a workshop with an attached guest house and bath. I have three options for hot water.
1) Tank electric
2) Instant electric
3) Instant propane

We do not have natural gas on the property but I do have propane. I would have to run a gas line another 30 feet to bring propane to the heater. If a tank type it would be a Rheem Marathon 40 gallon that is pretty efficient, and a lifetime warranty plastic tank. I've used this in other homes and they are fantastic. Cost about $1000 for a 40 gallon. The plumbing/Mech/elec engineer says I need a 13KW electric instant, a well rated Reehm is $425 and a bit larger wire so a bit more to install. The gas unit is about double and I assume it would cost more to plumb the gas than to run electric. I've never owned a tankless, how do they hold up for occasional use? With the Reehm marathon, I know they don't leak. Eventually an element will die. The tank type will be hot all the time so it will cost more to run. I intend to live in this house 20-30 years.

What about a small tankless?

I'd probably go tankless, since it sounds like this is an occasional use situation.

quote:

Originally posted by LS1 GTO:
What about a small tankless?

He listed three options. Your suggestion is #2 on his list.

For occasional use, I'd be inclined to go with whichever tankless option would be least expensive imstalled.

If you're going to run propane for heating the room then I would probably opt for propane tankless. If you are using electric to heat then that's what I would use for the water.

For casual/intermittent use go with a standard electric and use an electrical plug or a disconnect. A cold tank with fully heat in 30-40 minutes, leave it off unless it is to be used. Replace the anode rod yearly and you will likely never replace it. The life of a HWH is like a fuselage, expansion/pressure cycles. Most economical way to go, now and over time.

I have a guest house used like you say yours will be. We installed a propane tankless in it about 10 years ago. It has been a maintenance and repair headache since installed. They don't like hard water or sediment from a well. We installed a filter to deal with sediment, which helped some, but mineral buildup is still an issue. I regret having not just put in a moderately priced electric tank type WH, which is what we did in an adjacent house that had the room to do so. I replaced the elements it originally came with, using "sand hog" elements, when it was installed. Since then, it has been entirely trouble-free. I turn off the breaker powering it when it is not in use.

May I suggest a 30 gal Marathon electric unit. I have one in my shop, another in the guest quarters and two in the house, one 50 and one 40 gal. Never had any issues and the Marathon has a tank wall thickness of about 4". Hold the heat very well and they are moderately priced. Usually sold through your electric company and that is how I got mine. BTW, I have propane in the shop for heat and in the house as well. Good luck.

quote:

Originally posted by arfmel:
I have a guest house used like you say yours will be. We installed a propane tankless in it about 10 years ago. It has been a maintenance and repair headache since installed. They don't like hard water or sediment from a well. We installed a filter to deal with sediment, which helped some, but mineral buildup is still an issue.

True, very true... if you don't have good water, skip the tankless!

quote:

Originally posted by Excam_Man:
True, very true... if you don't have good water, skip the tankless!

Not so much.

When I turn on my faucets, gravel and nails comes out (very hard with a ton of iron). I flush the tankless once or twice a year with vinegar and swap out the filter then as well. No issues at all.

I do agree, though, that the tankless seems like a bit much for the intended use. I'm in the same boat trying to decide what to use in my new shop. I've decided to go with what sunburn suggests and put a small 20 gallon (or so) electric out there and only heat it when needed.

Workshop needs and guesthouse needs sound very different. If the guesthouse will be used by more than one person at a time I'd worry about 20n gallons being enough when it comes to showers. If you have the room for a 40 gallon it might be the better choice.

Get the 40 gallon and turn the heat down to the lowest setting when nobody's in the guest house (or even off).
Warm enough to wash your hands, won't cost much to run.

Our shop/guest apartment water heater is a 40 gallon electric. It gives plenty hot water for our guests and when no one is there we pull the breaker.

40 gallon is likely less expensive than a 20.

Tankless water heaters have come a long ways in the last 10 years. Maintenance still has to be done but it isn't nearly as bad as it used to be. I would say the scenario you laid out is the absolute perfect application for a tankless.

I've never seen an electric one I like. Your intention to stay there long term just enhances the case for the tankless solution.

Mark

When I had a whole house generator installed, my propane guy ran the line labor and materials for free.

I see you are in Arizona. Is it cold where you live? Just wondering if a type of solar heat might help offset any choice you might go with.