Home built indirect DHW tank?

[Badfish740]

I was searching around online for information on indirect hot water tanks for DHW with two heat exchangers (one for the boiler one for solar) and was pretty surprised by how expensive they can be. Basically $1000 and up from what I saw. Has anyone done their own indirect tank? I was thinking that a 100-150 gallon propane tank properly insulated and fitted with a pressure valve, etc...would probably work pretty well. Of course, the labor, heat exchangers, etc...could end up exceeding that $1000 cost. Anybody have any good ideas?

 

[Tarmsolo60]

unpressurized storage with two coils in it. I think it would be harder to do with pressurized.

 

[Tarmsolo60]

actually what your trying to do I think you would need three coils in an unpressurized setup. Manufactured indirect might be cheapest way out.

 

[kabbott]

I have considered a custom tank myself made out of stainless but by the time I buy the materials.... it's just not much
cheaper. For whats it's worth... I would not bother with a steel tank, A plain steel tank not last 10 years with my well water.

 

[benjamin]

I've looked for a cheaper alternative too. Besides one nice used solar tank I haven't had any luck.

I wouldn't want a propane tank for DHW, but there are plenty of used water heater tanks around that could be converted. There are many commercial or milkhouse units that are 80 gallons plus. I've tried a 3/4" copper coil around the base of an electric tank, completely ineffective, it needs some kind of heat transfer compound. I'm thinking of pulverising aluminum cans and mixing with silicone caulk or epoxy to make a heat transfer "mortar".

Maybe there's a reason most people end up using sidearms or flat plate hx's.

 

[ewdudley]

I was searching around online for information on indirect hot water tanks for DHW with two heat exchangers (one for the boiler one for solar) and was pretty surprised by how expensive they can be. Basically $1000 and up from what I saw. Has anyone done their own indirect tank? I was thinking that a 100-150 gallon propane tank properly insulated and fitted with a pressure valve, etc...would probably work pretty well. Of course, the labor, heat exchangers, etc...could end up exceeding that $1000 cost. Anybody have any good ideas?

I built a separator tank/buffer tank/indirect DHW tank that I finally finished plumbing-in today. We've got a wood boiler with storage and the oil boiler, so I wanted to be able to draw heat from either boiler and still have DHW. Plus I needed a coil to provide heat for the if-you're-going-to-put-in-a-wood-boiler-I-guess-that-means-I-can-have-a-hot-tub hot tub.

We've got about $120 into it not counting the coils or the insulation. The necks and flanges I bought new, which accounts for over half the cost; if you were more ambitious than me you could build your own.

For solar I guess you'd need a 100 gallon tanks to start with and then stick coil in sideways at the bottom, unless the solar subsystem was closed in which case you wouldn't need another coil.

--ewd

 

[Dune]

I have gotten two SuperStor tanks so far from my neiborhood plumbing supply. They were returned under warrantee for tank leaks. They have stainless tanks. One, which is 120 gallons has two coils inside. I will eventualy swicth this with the 40 gallon tank I am running with a sidearm. The stainless was cracked at a fitting and easy to fix with a tig welder. There are presently a few more at that same Supply house but I have what I need. Check around.

Finding the 120 with the two coils in it moves me much closer to solar DHW.

 

[btuser]

I've been on the same hunt for a while. A few tanks in series/parallel configurations seems to be the cheapest setup, because its much more common to find a 40 gallon in great shape than a larger tank w/ the second HX. For my draw I'm going to need about a 120 gallon indirect for solar. Tough to find used.

 

[mikeyny]

I built a simple tube in tube heat exchanger . 6 ft of 2inch iron pipe with 1/2 inch copper finned tube going thru it. I plumbed it into a 5 gal water tank for storage. Very cheap and simple. You could build one for each set up. All of my parts were used or cheap and it makes all of our hot water when the wood boiler is on. I also have a home brew hot water solar panel on the roof that uses the same tank. By 4 pm on a sunny day I get 50 gal of 80 to 100 degree water and feed that into my gas fired water tank. I call it a hot water pre-heater.
Mike

 

[benjamin]

I've been on the same hunt for a while. A few tanks in series/parallel configurations seems to be the cheapest setup, because its much more common to find a 40 gallon in great shape than a larger tank w/ the second HX. For my draw I'm going to need about a 120 gallon indirect for solar. Tough to find used.

I sort of know how that goes. I bought a 120 gal solar tank with a 2 year old system, but it wasn't cheap.

Indirect hot water tanks are virtually unknown around here. I can find all of the electric or gas scrap units I want, but have never seen an indirect of any size or condition, until this solar one came along.

Sounds like Dune hit the motherlode.

 

[btuser]

Most of the solar tanks I've found have been electric backup, which would be great save the cost of installing electric + the cost of my state's electric rates. I was thinking of a larger tank in the neighborhood of 300+ gallons that I could dump all the heat I needed, then use it to pre-heat the cold water. Problem is this tank would have to be outside, so I'd have to worry about serious standby losses.