Domestic hot water

[maplewoodshelby]

I'm a little confused. Can someone tell me in simple terms and very briefly the different setups to heat dhw with wood stove. The stove I just bought has a built in DHW coil. So the way i understand it, I will need a sidearm heat exchanger at my dhw. Fill the stove with water and it circulates to the dhw, thru the heat exchanger, and back to the stove in a closed loop.(no new water in or out of this loop) And I am guessing I will need a circ pump for this line as my dhw is quite a ways from my stove.
I have two DHW tanks, one is about 30 gallon and one is about 80. The small one runs the kitchen. Could I hook these two DHW tanks up in series. And if so which one first? The small one is close to the boiler and in line with the big one which is about 90 feet on away from the boiler

 

[jebatty]

I'm a little confused. Can someone tell me in simple terms and very briefly the different setups to heat dhw with wood stove. The stove I just bought has a built in DHW coil. So the way i understand it, I will need a sidearm heat exchanger at my dhw. Fill the stove with water and it circulates to the dhw, thru the heat exchanger, and back to the stove in a closed loop.(no new water in or out of this loop) And I am guessing I will need a circ pump for this line as my dhw is quite a ways from my stove.
I have two DHW tanks, one is about 30 gallon and one is about 80. The small one runs the kitchen. Could I hook these two DHW tanks up in series. And if so which one first? The small one is close to the boiler and in line with the big one which is about 90 feet on away from the boiler

Since you have a DHW coil in your stove, you should not deed a sidearm. The sidearm is used to heat water when you don't have a DHW coil. You will need a mixing/tempering valve somewhere in your DHW system to make sure that water delivered for use is not too hot. The water coming off the DHW coil could be scalding hot, up to the water temperature in your stove.

You may or may not need a circulating pump, depending on how hot you keep your stove, how well the DHW water coil works, and how much hot water you use. Usually domestic water pressure simply moves "cold" water through the DHW coil when a hot water faucet is turned on, thus heating the cold water to hot, and then delivering the hot water to the faucet.

How you plumb the hot water tanks for interim storage becomes a separate issue, and can get a bit more complex. It seems to me that, ideally, you would have a circulating pump and control system to circulate hot water from storage through the DWH coil when the stove is hotter than the storage, thus heating the storage. You might consider a differential controller for this.

In all cases hot water for use would be drawn from storage using the domestic water pressure. As hot water is drawn from storage and storage temp drops to below stove temp, then the differential controller would start circulating storage through the DHW coil to heat storage. Hot water from the DHW coil should be supplied to the top of the storage tank with return to the DHW coil from the bottom of the storage tank. Hot water for use from storage should be drawn from the top of the storage tank, with new water resupplied to the bottom of the storage tank.

How you plumb the two tanks is a matter of choice and may depend on which one you want to have priority, that is, which one needs to be sure to have the hottest water.

Since I do not use this kind of setup, I'm speaking from my own logic. Others may have better advice.

 

[maplewoodshelby]

Thanks for the reply. Forgive me as I have very limited knowledge of hydronics
My stove is the Energy King 450 and I'm still deciding but probably not going to have storage.

What I get from your post is that the DHW coil on the stove basically acts like a stand alone domestic hot water tank.
So it is not a closed loop thing but actually the dhw coil needs to be supplied by the water line and the force of the water pressure will move hot water from the DHW coil(on stove) to my existing hot water tanks (which I can now turn off power) and then throughout the house?

Am I correct in this thinking?

 

[jebatty]

I don't think so. The DHW coil is like the heating element in an electric hot water heater. It simply heats water passing through it. The "storage" I was referring to was your two hot water tanks; that is, they will store hot water heated by the DHW coil until you have a need for hot water. Perhaps I don't understand what you are asking.

 

[Nofossil]

One very classy solution is to mount your DHW tank (which could be an electric hot water heater) so that it's higher than the coil in the wood boiler. Plumb the coil to the top otlet and bottom inlet of the DHW tank using tees at the tank. Make sure you have a mixing / antiscald valve after the tee on the tank outlet.

Any time the boiler is hot, it will circulate heated water to the DHW tank by gravity (also called thermosiphon). No pumps, no valves, no controls.

If the coil in the wood boiler has a top and bottom, they should be connected to the top and bottom of the DHW tank to encourage gravity flow.

 

[maplewoodshelby]

Well I'm trying to figure out how to do a diagram on here with no luck so i will just tell you


BOILER------------30 gallon tank-------------80 gallon tank

The thermosiphon method is not an option for me as my tanks are lower and far away from boiler.

The first tank is about 15 feet away and it is the 30 gallon then farther in the same direction another 50 feet is the 80 gallon tank.
So I'm looking for ideas on piping this

Here is my basic understanding and plan

Starting at the stove. DHW coil then go with relief valve, then pipe to first small water heater and tee in with the cold water in pipe, (install valve on cold water in pipe above tee so i can control) At the hot out of the small tank install tee, one pipe going to kitchen (as original) and then one pipe heading toward the big water tank 50 feet away, tee in on the hot side of the big tank, at the bottom pressure valve tee in and run back to the boiler.
Now does anyone think this will work and where would you insert your circulating pump? I also realize I have left off eitehr tempering valves or mixing valves but I will get to if you guys will think this will work

On the first tank tee in with the cold water line, If I put a valve above the tee in on the water line then i could turn it closed in winter (kind of taking it out of the supply line) and open it back up in summer when not burning wood thus not using DHW coil to heat water

Tell me what you think fellows

 

[maplewoodshelby]

Anybody got any thoughts

Sammy

 

[tom in maine]

Let me throw another concept out there:
I cannot take credit for this although it is rather self serving.

Install your coil in the wood stove and then run it to an unpressurized tank.
Pump unpressurized tank water into the coil and back to the tank.
Of course, you need another heat exchanger to interface with your plumbing system, but there
are several advantages.
1. It is explosion proof, since it is unpressurized and should have no shut offs on the system. You should still install pressure relief
valve(s) for redundancy.
2. There will be no buildup of scale in the wood stove coil which regularly happens in coils that use household water. The tank water is only put in the tank once.


You need a pump large enough to fill the system, but the head height is usually not very high.
We have done these systems and they work very well.

Prof. Dick Hill from the University of Maine--the Godfather of all gasifier wood boilers suggested the concept to me since we were building
these types of tanks.

 

[maplewoodshelby]

[coloPump unpressurized tank water into the coil and back to the tank.
Of course, you need another heat exchanger to interface with your plumbing system, but there
are several advantages

So basically your saying from the stove, pipe to unpressurized storage, then from storage, pump to water heaters and use heat exchanges on water heater.

Seems abit overkill although I do see the advantages you are talking about. I'm not worried about replacing the coil in the stove as it is easily replaced and I would not have to deal with heat exchangers and two seperate pumps

 

[smokinj]

One very classy solution is to mount your DHW tank (which could be an electric hot water heater) so that it's higher than the coil in the wood boiler. Plumb the coil to the top otlet and bottom inlet of the DHW tank using tees at the tank. Make sure you have a mixing / antiscald valve after the tee on the tank outlet.

Any time the boiler is hot, it will circulate heated water to the DHW tank by gravity (also called thermosiphon). No pumps, no valves, no controls.

If the coil in the wood boiler has a top and bottom, they should be connected to the top and bottom of the DHW tank to encourage gravity flow.

+1 This works great without the pump

 

[tom in maine]

There are two plumbing setups with an unpressurized system:
First, you pump out of the tank into the coil and back to the tank again, circulating tank water.

Second, you have a copper coil heat exchanger in the tank with a tempering valve, that ties into the household DHW system.

Since the DHW part of the system sees no fire or high temperatures of the fire, there is minimal to no scale buildup and much less likelihood
of an explosive failure. If the tank did get near boiling, you would hear it percolating. (Which is pretty cool!)

It is not as cheap as the other pressure systems, but it allows a larger storage tank and is half of a solar DHW system. Just add collectors and another pump and
you are in business.

Tom