Question on indirect tank setup without also having a hot water heating system

Where is this vacation home? Straight Electric heat is really expensive.

On demand water heaters have their good and bad. Water quality plays a big part in the decision. What size also.

You can get stainless or plastic electric water heaters from a number of manufacturers if corrosion is your concern. Check that the water chemistry is compatible with the tank, especially water with high chlorides can be tough on stainless or plastic tanks.

Your question is very confusing to me I admit. You have gas but instead of buying a new gas water heater, you want to set up some kind of indirect tank? What is your imagined benefit here?

when you start to get your electric bills for that electric baseboard, you will reconsider.

consider getting a small gas furnace, but keeping the baseboard as your back up.

Check your local energy costs LP vs Oil. A small combi boiler on LP gets you DHW and you add hydronic heat as you go, radiant, panel rads, etc.

I suspect LP may be cheaper than electric heat. Unless a heat pump is an option? But check some of the online sites that have history data, EIA for example.

https://www.eia.gov/state/analysis.php?sid=VT

Flo says she has natural gas

Last I knew Vermont doesn't have much NG. I am trying to think if I worked on any NG burners up their.

I might be one of the few folks here that have been involved with just this scenario.

In the 1980s the family business diversified into becoming a distributor for Buderus Boiler and Riello Burner. As a result of this combination of selling boilers and burners to contractors we also sold them to the family fuel dealer that installed new equipment. At the time our summer home in NJ was heated with electric baseboard and used a 50 gallon electric water heater for two bathrooms and an outdoor shower 

An addition was planned that included a 120 gallon jacuzzi with 8 water jets and enough room for 2 adults at the same time.  The 50 gallon water heater was not going to cut it for filling the 120 gallon tub.   So we installed a Buderus oil fired boiler, and a 40 gallon indirect.   That setup never ran out of hot water.  

Eventually the addition had a third bathroom added and we heated that room with a Buderus towel warmer using a TRV and there was a game room added that we connected three buderus panel radiators to the boiler.  But for the first three years that indirect was the only thing the oil fired boiler operated.  

Eventually that building was demolished in favor of a much larger duplex to maximize the value of the property  That Buderus was about 6 years old by then so it ended up in my own home about 8 miles from the original location and it is still pumping out heat with a combustion efficiency of 84.6%.  We are heating two radiant floor zones, two air handlers with duct coils  and an indirect. 

Shelburne? Then you probably do have natural gas. That's one of the few areas of Vermont which does…

In which case do your sums, but I'm going to suggest that you might get away with a combi, if your heating load and domestic hot water loads are comparable, or else a mod/con for the heating load and an on-demand gas fired hot water system.

This is also one of the relatively few situations where the cost of installing the hot water heat can be recovered in a reasonable time frame. You first electric bill running the electric heat should be opened only while sitting down with a stiff drink handy…

When a heat pump water heater has a mean time between failures measured in years, I will. When it's measured in weeks, if not days… sorry, no sale. I know of one off-grid resort installation with six of them. When they are working, they're great. But… the resort has to have one engineer whose half time job is keeping them running (the rest of his time is spent keeping the solar array and battery system running, but that's another story).

When a heat pump water heater has a mean time between failures measured in years, I will. When it's measured in weeks, if not days… sorry, no sale.

Please provide a reference for that MTBF number and also for gas water heaters, thanks! Mine's at 5 years so I don't think it's measured in days unless I'm the luckiest boy in the land

From what I see HPWH are not gaining momentum. Too much money to spend on a throw away appliance that no one wants to fix.

Definitely a bet I'd take! But sorry for hijacking and respect to you both.

Gosh solar thermal and PV should be pretty hands off these days. A drainback ST with only one moving part and a simple control has little to fail.

We put a large ST array on a YMCA camp in Missouri, rubber pool collectors as it is summer use only. Flip a switch every summer and fall and it provides over 80% of the DHW. It's been running trouble free for at least 10 years.

Your systems must have some archaic controls if they are that problematic.

I don't see a HPWH being much more complex than a refrigerator. With a back up element you should never be without DHW.

The weak link in any tank type water heater, gas, electric, HP seems to be the tank life itself. An electronic anode or one of the stainless tank type would handle a lot of those concerns.

Also have a stiff drink ready when you receive the quote for the modcon+baseboard retrofit. You'll need something MUCH stronger than when opening the utility bill.

A reasonable cost save is to install one or two wall mount cold climate mini split heat pumps in the main living space that can carry say 60% of your heat load. You still use the resistance baseboard to even out the heat in the place around the perimeter but now your bulk heat would cost about 1/3 less. Bonus, free AC in the summer. This will be significantly cheaper than a hydronic retrofit and much less intrusive.

Your heat load is pretty easy to figure out from your utility bill. Once you have a cold month heating costs, you can do the math here (you'll have to convert your kWh to Therms for the math).

https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler

Which is what I said…. ^^^