Help on plumbing for thermosiphon

Richard,
I agree that system would be ideal.Much more so in a boiler than a stove.I just can't get my brain around it.I sat here last night drawing pictures and refering to you posts and I still can't see how the gravity part of the system works.I'm not saying it doesn't work but,with the simple science of your system I can't seem to figure it out.
DON

Everyone need to remember that the simple 'U' coil in a stove is NOT the same as an 'instant hot water coil' in a boiler.. The long, finned 'instant' hot water coil in a boiler will raise 50* water to 140* water at the rate of about 5-10 gallons a minute, if the boiler is at 160-180*.

The HilKoil 'coil' in a stoker stove will barely raise 50* water to 70* water if you are running the water from the street through the 'coil' to the sink. These Hikoil 'coils' are meant to slowly heat a 40-50 gallon tank of water to 140*+ overnight or during the day,, over an 8 hour or more period of time..

This is why a thermosiphon system works,, it is slow, but steady, and will keep a tank of water hot or heat a tank of water 'for free' overnight.

I would never run well or street temperature water through a Hilkoil 'coil' in a stoker stove.. use the coil as an auxilary heater for your HWH. Or best, add a tempering tank prior to the cold water inlet to the HWH, and use the 'coil' to heat the tempering tank.. this way the HWH never gets street or well temperature water,,

Any way you plan on plumbing it, the small, in-stove coils do not turn the stove into a boiler,, there is just way too little heated surface.. I think SteveN told us that a HilKoil 'coil' was good for about 5K btu per hour.. not a lot. [ my memory may be off on this number, but it was a small number]

Hook it up as a simple thermosiphon, if you are not happy, install a small circulator in the loop. Either way you are storing heated water for your morning showers, and afternoon/evening laundry... [at least that is how it would be in my household].

Greg L

LsFarm wrote:The HilKoil 'coil' in a stoker stove will barely raise 50* water to 70* water if you are running the water from the street through the 'coil' to the sink.

Which is why I would still disagree, 20 is better than nothing. How many times a day do you use short bursts of hot water for washing hands etc. In that case you're heating 70 degree water that's already been tempered by the room temperature... Just my opinion but you should try and get everything out of it you can. the only difference with the way I have it set up is you're forcing it into the coil first and changing the entry point into the system. In other words there is no reason not to do it.

If you take the last drawing posted by cecil. If you capped the inlet where he had the cold going into the hot water heater and tied the supply to the yellow pipe from the drain you'd have the exact same thing I posted except you're using PRV outlet for connection...

I would let the Hilkoil stay hot, in the firebox, not introduce sudden shocks of 50* water.. the very hot [usually] thermosiphon-heated HWH will absorb the short use of hot water for washing your hands. That's what the HWH does. Only when enough cold water is introduced will the heating device turn on.

The Hilkoil is meant for slow and steady heating of a tank of water, it isn't an instantanous heater... My guess of a 20* rise is a guess, it really depends on flow rate.. and the length of the 'coil', and the temp in the stove, if the stove is idling, or at full fire, etc...

Hilkoils are for slow and steady,, instantanous [imersion] coils in boilers are for continous high-btu transfer of heat. The coil is many feet long, and is finned, and immersed in hot water, and the coil is usually copper,, all favoring transfering a lot of BTU's per hour.

Greg L.

Another thing that will happen with cold water running through the Hilkoil is if you have the stove or furnace off in the summer it will condensate.
DON

Does anyone have any idea how many gallons would move through the coil with a siphon method?

It's hard to say.I will say the coil I made for my wood stove would heat a 30 gal. tank from cold to 170F ish in 45 mins.But it would never get much hotter than that.I think at that point the tank would loose heat(uninsulated) as fast as it would gravity.But the temps in a wood stove go up and down,coal heat is steady.Coil size,piping size and distance all play a part.

I have a 120 gal. electric water heater and all this talk has got me thinking.After all I'm thrifty(CHEAP).
DON

I think, all of you could benefit from a Google search for "solar hot water" and then take a look at their diagrams, with a coal stove in mind, rather than the solar. There are "closed loop" and "thermosyphon" systems.

Naw,seat of your pants.LOL
DON
Oh diagrams...they have pics? I'm in luck.

Yup, Cecils last sketch is a keeper. Certainly if all pipes sloped in the direction of flow it helps. In my mind it doesn't matter if the hot from the coil goes to the PRV or the hot out. If it goes to the hot out, water in the coil does not move (other than siphoning) while the tap is on. If you don't belive me, climb on in there with a scuba tank and some red food coloring. Have someone turn on the water as you drip color near the coil entrance.

I do like Richards idea of having street water go through the coil when the tap is turned on IF the thermal shock doesn't hurt the coil. Only time would tell.

Why do we call it a PRV (pressure relief valve) when actually it's a T&P (temperature & pressure) valve?

Back when I was doing plumbing we sometimes talked about how plumbing is a sport in which the job can be done several different ways & will not only work, but work well. This thermo set-up is a prime example.

Freddy your're right but I'm refering to the drawing Richard posted with the check valve on top of the tank.No check valve no problems.You can tie the hot from the coil anywhere on top of the tank.
DON

In no part of diagram is there a check valve on the top of the tank, it's on the return line from the drain. I'll explain it again.


1. This is the cold water from the street, the check valve here is to prevent water from backing up into the cold water line.

2.It enters the loop, it has no where to go except into the coil.*note I'm using green for the yellow pipe because yellow font sux

3. It exits the coil and goes into the top of the hot water tank on the cold water inlet(it was discussed hooking it to the outlet may be better).

4.It exits the hot water heater from the drain plug through the check valve into the coil completing the loop.


The orange pipe is the regular outlet that goes to the faucets.

It's the exact same thing you're doing except where the water is coming into the loop and I'm forcing it through the coil first.

I don't think it's a good idea to put cold water into a hot coil. There are many more problems when you have a coil in a wood stove because of the uneven heat so I wouldn't want to chance this. I also don't think you would gain much anyway because you'll need to turn over the tank to get all the water hot anyway. I would love to test out all these theories and see who had the best plan of attack for this type of system and how much actual flow you can get. Common sense tells me that once the tank starts to get low from taking a shower the little coil that they sell is not going to be able to keep up but it will take a major load off the electric/gas/oil DHW.

Got the line from drain to bottom of coil replumbed. Now that i'm plumbing the line from the top of the coil to the PRV (or T&P valve for Freddy) I now have another question. The opening for the T&P valve is facing away from the stove and at a goofy angle. I still have the valve I installed on the outlet of the coil, do I still have to have one at the tank? It's only 1-1/2 to 2 ft from the valve at the stove. Don't know if it makes much sense being they would only be about 2' apart. The one next to the stove is brand new, so it should work fine. A simple little project has turned out to be quite an ordeal. Thanks again everyone.

Jeff

ceccil wrote: do I still have to have one at the tank?

Absolutly, positively, without a doubt, yes. We're stretching the code to have a tee between the tank & the PRV, to have it further away would be a bad thing. The PRV blows off when it gets too much pressure OR too much temperaute . By having it more than a few inches from the tank removes it from it's assigned place of duty where it can sense the heat. If you only want one PRV it has to be on the tank.