Help on Plumbing for Thermosiphon

Got coil installed and had some questions on plumbing. I'm running my water out of the drain on the tank into the bottom side of the coil. I plan on raising the tank using blocks. The outlet on the tank will still be about 2" lower than the inlet on the coil. Is this acceptable? I'm also installing a 2nd PRV (one on the tank and one between outlet of coil and inlet on the tank) and going to tie them into each other down the line and vent to the outside. Last question I have is, if I start making to much heat can this be dumped using one of the finned baseboard units using the thermo method or is this only an option using a pump? Any other suggestions or comments? Let e'm fly. Thanks.

Jeff

No need to raise the tank. As long as it's within 10 feet (which it is) and on the same level it''ll thermo just fine. What you're doing looks good so far. Make sure that there are no valves between the PRV's and the pipes or tanks (looks like you're good so far). If all valves are shut off, the PRV's must still work. I think you may plumb the PRV's together and out.I don't think code talk about two PRVs together. Again, no valves. I might plumb them seperatly, and do it with as few elbows and as short a run as you can. The idea is to make it an easy path to blow off.

The overheat... I wouldn't worry about it. From what I've read they are designed well and rarely give a problem. If it does, then cross that bridge. I'm not sure how you'd make a dump zone. If you made a thermo siphon one, it would be hot all the time, not just when it overheats. If you put a pump on it, you'd need an aquastat. Kinda complicated for something that'll probably never get used. Maybe someone else has better words for a dump zone.

I had some of these same questions and this thread may be of some help to you:

Thermosiphon Question for Coil

-Len

Looks good.I don't think you'll have to worry about a dump zone.You're using a gas water heater and should have ample heat loss(stand by loss) up the chimney.Try it without insul on the siphon lines if you need or want more hot water insulate them.
DON

One more thing the top line off your coil(hot) should be hooked to your hot line on the water heater pitching up slightly.The bottom off your coil (cold) should be pitching slightly down toward the tank.

Here I go again.Don't keep that boiler drain upside down on the tank. The line will fill up with lime and crud.

Looks like i'm doing ok so far then. The tank is going to stay about where it sits now. It's going to be plumbed like the drawing below that traderflp drew up. The only thing different will be the drain, and another PRV in line between coil and tank.

That diagram isn't going to work.... the top of the coil need to go to the top of the tank. The bottom of the coil needs to go to the bottom of the tank. I see no need for a swing check, but one wouldn't hurt. I didn't put the drain(s) or valves in the sketch.

One other thing.... You'll probably want to have a mixing valve so water coming from the tank to your domestic use is not too hot. If you get the water up to 170 or 180 degrees in the tank you'll be taking skin off in the shower.

I don't think it's make a big difference if the cold water coming in goes through the coil first or directly to the tank. When you turn on a faucet the water wouldn't be in the coil for more than a couple of seconds.

Shouldn't the hot from the coil go to the hot on the tank?
I've never hooked a coil to a regular tank just to a range boiler.They have separate tappings for a coil.

Yup, good point, and that's why the check valve is needed!

The drawing I made above was to help me sort out the thermosiphon sketch that Richard posted. In the end, I decided to use a small circulator. Here is a pic of the coil. You can see the relief valve which is to the right of the valve on the coil. I think I need to add a PRV on the coil too. Not sure.

Please tell me this will work!! I worked on this a good part of the day and it's how I have it plumbed. Also found out just how much to tighten down the pex fitting on top of the tank (about a 1/2 lb less than I tightened it) cracked the fitting and had to run all the way back up to Lowes to get another. Got all done, filled system and bled air. No leaks as of now. Thanks to all for your input. Makes life easier. I didn't add a mixing valve as of yet. Talked to a few people about my setup and they say it may not get as hot because the coil is off to the side of the grate instead of being over top. Also going to leave pipes uninsulated. Will see how hot it gets. Will add mixer later if needed.

Jeff

ceccil, A swing check valve will only works in the vertical position if the water is running up-wards.

Very good point Don't know why I didn't realize that. The bottom one is flowing in the right direction but using thermo the water probobly isn't moving fast enough to open it. Well, back at it tomorrow. Thanks.

Jeff

You mayhave made the mistake I made in my first sketch. The hot from the coil shold go to the hot of the tank. The reason is that the cold from the tank has an internal pipe that goes to the bottom of the tank. With the hot from the coil going to the cold of the tank it will not "turn the water over" in the tank. It will tend to just make a mini circle at the bottom.

I'm not sure if a swing check will work vertical on the other pipe either unless it's pumped. Horizonal will work fine.

I would have left the hot and cold water lines hooked up to the tank the way it was with a mixing valve of coarse.What you did on the bottom of the tank was fine(connecting the bottom of the tank to the coil like it is)I would connect the hot(top) of the coil to the relief valve port and put the relief valve in the run of the tee right next to the tank.This way the 1 relief valve would take care of both the coil and tank.Connect the bull of the tee in the relief valve port to the hot(top) side of the coil.No need for any check valves.But that's just me.
DON

Freddy,
After thinking about this last night 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.
If you hook it to the cold at the top of the tank I don't know if it will thermosphon because of the drip tube in the tank.
DON