Small tank for water heater

[Cornerstone Const.]

I want to route my hot water from my boiler through a small tank that is lined with copper tubing. The idea is that I can re-route the supply for my propane domestic water heater to pre-heat the water before going through the water heater. That will give me domestic hot water on demand. Any thoughts? Recommendations?

 

[Nofossil]

There are many approaches to getting hot water from a wood boiler. One of the simplest and most common is to use a 'sidearm' heat exchanger to heat the water in a domestic hot water tank, which can also be heated with its normal heat source for backup when the wood boiler isn't running. Tanks is series are also not a bad idea, and done fairly often.

Do a search on sidearm and see what you find.

 

[Cornerstone Const.]

I have made several side arm searches and what I understand is that the (passive) thermal flow will heat the water, in the tank. However, we many times have guests that create a large use (one after another) and I want to avoid the propane use in this situation. I have also explored the idea of plates which seems more feasible than the side arm. I thought that a small (30-50 gal) tank that is tied into the boiler circulation system with copper coils in the tank would provide all our needs as we need them. It would also serve to add some heat in the cellar. I'm not saying I know all that much, I do not. That is why I'm here asking the questions to those of you that have done this a long time, and before I go with a later regretted decision.

 

[in hot water]

That is what is know as a reverse indirect tank. Where the boiler water is in the tank volume and the domestic water flows through the coil inside. The intent is to raise the domestic water temperature as it flows through the coils in the tank. Check out some of the brands that are available like ErgoMax, TurboMax, Everhot, etc.

It usually takes a bit of copper coil to get the HX rate. ErgoMax generally have 3 or more coils headered together inside. Basically a tank full of copper is what you get..

It does take a lot of BTUs and fairly high temperatures to drive them. Of course it depends on your incoming water temperature also, just like a gas fired tankless water heater..

Some guys use a double coil indirect like a SuperStor with cupornickle coils. Connect solar to the bottom coil, boiler water in the tank as a buffer to the hydronics, and the upper coil as the preheat to the standard water heater. This way one tank serves 3 functions.

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[Nofossil]

One solution is to heat the water tank (or preheat tank) way above normal hot water temps, then use a mixing valve to mix the really hot water with cooler water to get the correct temperature at the faucet. That can stretch a tank quite a bit.

 

[Cornerstone Const.]

The super tank is nearest what I was thinking about. Any idea of cost before I get plagued with sales?

I was thinking of not having an insulated tank to aid in heating the cellar.
I use a combo of water to air exchanger in the furnace and pex in floor to heat my house.