Help on plumbing for thermosiphon

This is how ours was set up BIG BEAM, plumbing wasn't exactly the same because our coil has two pipe same height on the back of the furnace.

BIG BEAM wrote:No need for any check valves.But that's just me.

I can understand your point about the check valve on the colad water inlet especially if you're blowing PRV. I also note more than few people have already set it up this way and I haven't heard anyone mention PRV troubles. As far as the one in the loop, don't you think it's practical to insure it's going through the coil first? The idea is to make it as economical as possible and extracting as much heat from the coil is first and foremost and sending cold water through the coil first when its at its coldest would be how you would accomplish that.

BIG BEAM wrote:if you hook the hot from the coil to the hot on the tank when a tap is opened the hot from the coil will go right into the hot water line bypassing the tank.

No it won't. Water takes the path of least resistence.
Take a look here. They show a diagram of how to hook the one they sell up.

http://www.therma-coil.com/plumbing.htm

Richard makes a point. The heat picked up during a quick pass might not be much, but any is more than none! Maybe it should be done similar to his idea.

Freddy look at the pics
What will make the water go into the tank if the hot coming out of the coil is connected to the hot on the tank and a tap (hot water) is open?
DON

Freddy I just looked at you link and that is just what I said to ceccll on how I would do it.

That pic freddy linked to should be the "standard" we use here.One more thing some water weaters have their PRV on the top of the tank that is where you should connect the hot from the coil.Either location will work fine.

The reason I think that link should be the standard is because must of us on this forum are here to build systems that work at as low a cost as posible and still work well. KISS
After all we're all here because ...well we're cheap,I know I am.Maybe thrifty is a better word but that's not what my wife calls me.

One more thing .The tank doesn't HAVE to be elevated it will work better that way but is not mandatory.If the tank and boiler were both on the floor the thermosipon will most likely produce 1/3 -1/2 gals /min(3/4" pipe).In a 40 gal. tank thats 1.5 hrs.for a full tank and that's faster that electric.
DON

BIG BEAM wrote:What will make the water go into the tank if the hot coming out of the coil is connected to the hot on the tank and a tap (hot water) is open?

The water pressure coming in from the cold. Connecting it to the hot is no different than connecting it to the PRV as far as water flow is concerened. Either way when it's thermo siphoning, it makes the loop, when the tap water is opened water comes in from cold and out the hot. While the tap is being used the coil has equal pressure on both ends and the water in the coil does not move. (Unless you use Richards swing check to force it through the coil.)

Yup, the diagram in that link is a beauty, nice & simple & will work well.

I do like the idea of a second PRV very near the stove. When I first had my home made coil in my woodstove it had too much coil. The water would turn to steam and instantly collapse back below 220*. It would hammer! Ba-bang! I shortened my coil and had no issue after that, but I'll bet a PRV at the coil would have released a tiny bit of pressure and stopped the hammer.

Not with that check valve system.The cold water goes to the coil first,gets heated,comes out the coil hot then gets tied into the hot on top of the tank.It won't go into the tank because if the hot water tap is open it will go right into the hot water line.So the hot water isn't coming from the tank it's coming from the coil.I'm not talking about the thermosipon part of the system I'm talking obout when you draw hot water.
DON

I forgot
The coil I made for my wood stove did that hammer thing too.I had 10.5 ' of coil in my stove.That hammering just got things going.LOL Never hurt anything so I left it.
DON

Hey Freddy aint you supposed to be installing a boiler?How's it going?

Ok, here we go. Can we agree this diagram will work? Still going to keep the 2nd PRV. I just like the added security, just in case. Should I just do away with the check valves? I'm still going to hold off on the mixing valve until I see how hot it gets. Draining the tank was a pain. Was going to drain it into sump pit but pump wouldn't work. Had to drain entire 40gal. into 2gal. buckets and carry over to washing machine to dump. Gotta get that pump fixed!!

Jeff

I was going to plumb mine exactly as you have illustrated. I was told it would siphon but very slowly. I have no idea though.

BIG BEAM wrote:Not with that check valve system.The cold water goes to the coil first,gets heated,comes out the coil hot then gets tied into the hot on top of the tank.It won't go into the tank because if the hot water tap is open it will go right into the hot water line.So the hot water isn't coming from the tank it's coming from the coil.I'm not talking about the thermosiphon part of the system I'm talking about when you draw hot water.
DON

Since both hot water pipes (coil hot water and DHW feeds) are not connected inside the tank then some amount of mixing has to be going on. Wouldn't the amount of mixing be totally dependent on where the two hot water pipes end inside the tank? If the coil pipe ends right at the top of the tank and the DHW pipe starts in the middle of the tank then wouldn't that determine the amount of the mix? Check valve or not the water whether the tap is on or not is still going in the same direction.


Jeff,
You shouldn't need a mixing valve between the stove and the hot water tank, but you should already have one setup between the hot water tank and the feed to the house.

ceccil ,

Do it how you want but IMO it's pointless to feed a HWH with the feed from the street if you don't run it through the coil first. I'd venture to guess it would be more efficient to skip the loop and just run it through the coil into the HWH. Raising 40 gallons of water to X temperature consumes a lot more energy than maintaining it.

BIG BEAM wrote:It won't go into the tank because if the hot water tap is open it will go right into the hot water line.So the hot water isn't coming from the tank it's coming from the coil.

If the cold water "inlet" goes all the way to the bottom of the tank then no, whether you use the hot water "outlet" or cold water "inlet" for your source for the faucet it still has to navigate the entire length of the hot water heater doesn't it?

Freddy,

Love the diagram, and agree it should be standard for people to see how things are done since it points everything out very clearly.

Adamiscold wrote:Love the diagram, and agree it should be standard for people to see how things are done since it points everything out very clearly.

I'm building my "second furnace" now complete with coal bin and everything else. Once I have it done I'll be able to provide detailed 3-D images from any angle. Make panels transparent etc. For that matter I could bring them to life as video. If you've seen the some of the bin pictures I posted using it you'll know what I mean. Once I get it built, from there generating all kinds of images will be very easy, e.g I can color pipes blue or red, make new ones etc.

ceccill,
That's the way I would do it if it were my house.That's the way I did it 25 yrs.ago and it worked VERY well in a wood stove.
DON

Sorry,forget the check valves they're not needed.Rember to pitch the lines to and from the coil like you would a drain line at least.The more you pitch the lines the FASTER the system will work.
I bet by about now you're getting great at soldering

Don, I'll ask again why not send it through the coil first? Why use electric or gas to heat water when you're going to have excessive unused heat the coil can generate? In that setup you're only utilizing the thermo siphon action to heat the water. One other benefit I'll add to my setup is you have practically unlimited hot water. If you're using hot water it's all going through the coil first, if you deplete the volume of hot water in the hot water tank it's still hot because it went through the coil...