hot water from your wood stove thermo-siphon problems

[birdie4]

 great to see people are still talking about the hot water system from the wood stoves.

Got a question for you maybe you can help. We have had a thermo-siphon system for about 20 years works great! Last year we bought a new stove, same brand etc, but opted not to drill the holes in the stove and try them on the outside first. We looped it on the side and around to the front then back again and up the wall to the tank. At the tank in the attic we changed the pipe configuration slightly, because we actually added a second floor,  the pipe runs up the wall makes a 90 degree right turn then runs about 12" then another 90 degree left turn then into the tank. The problem is it does not seem to be siphoning and circulating properly into the tank. It is definitely getting hot and no pipes are running downhill or anything but this is absolutely driving us crazy trying to figure this out. Do you think you know what is happening or know someone who can help? Thanks for your help look forward to hearing from you. D & B

[fanman]

good moring birdie4,

sounds like to me its not getting hot enough, you say it is hot, im not for sure what temp is needs to be before siphon happedns, but i bet if you put the pipe back in the stove, it will start siphoning again, thats all i know

[birdie4]

Thanks but the reason I knew it was hot is I could hear it boiling at one point in the pipe at the stove and when I went up to the second floor and checked the pipe going into the tank it was not hot at the top? go figure, that is why I am wondering if the 90 degree, vertical, bends after coming out of the wall, there are 3 from the wall to the tank to the tank, may be the problem? Thanks

[Darren73]

hi,

can you sketch out the layout as you have it installed. I remember when the thermosyphon hot water system was installed in my parents the "horizontal" runs actually sloped up towards the tank at about 1" per 3 feet

Darren

[nick1234]

did you change the size of the hot water pipe.If i remember hot would be 3/4 and cold 1/2 due to the fact that hot water is lighter. No downs on the horizontals run slight up slope better. As for coil on outside of stove not much of a boiler. Cold water coil cools to fast by inrush of water you need a small tank(or larger pipe 2 inch dim.) as boiler bolt it to the stove (better inside)remember cold in bottom hot out top

 have fun

nick1234  

[birdie4]

can't seem to upload the drawing for some reason but let me try to explain it to you. the water flows along the side on the woodstove out at a 90 degree to the wall, up another 90 about 8", then 45 to the wall and up about 8'in the wall, once it comes out of the 2nd story wall it makes a right 90 over about 8" the left 90 about another 6" then a right 90 into the tank does this help? there are not really ny slopes so to speak but it does rise.

[birdie4]

Thank you for responding it does run up about 8 feet actually but it has alot of 90 degree turns, horizontal, Do you think that makes any difference?

[scottsAI]

Birdie4,

Two possible problems:

For a thermo-siphon to work, the hot pipe as it exits the stove MUST be sloping UP for several feet. No horizontal or downward dips. Will stop it cold.

The coil on the wood stove, the last segment going out must be the hottest and higher than the cold coming in. Once you have a few feet of Rise, horizontal and even downward dips can be somewhat tolerated. 90 deg bends slow the flow, should not stop. Basically since it was working before it should be fine unless added many more. Slow 90 deg bends are available in some pipes, much better for this application.

If there is a hot spot within the loops which is higher(above) than the output pipe, it might not work (starting problem). The hottest water must be allowed to float up like a bubble, downward it will not flow! Since I mentioned bubbles, no air must be in the pipes!! Starter pump can overcome some problems get it going then turn off.

The cold loop must start at the bottom (lowest point), wrap the next loop higher than the loop before. Spiraling up as you go around the stove (this is best). If an up/down loop is used the last segment of the loop must end at the highest / hottest point as it leaves the stove and is called the HOT pipe. The hot pipe must be insulated, not allowed to cool much going up.

How does this align with what you have?

Have fun,

Scott.

[birdie4]

Thanks alot for your help. It all sounds good and all of these things are in fact in place with one exception. When the plumber reconnected it this summer he did add about 3 more 90 degree horizontal angles and eliminated the slight slope upward in the attic that it had before. The tank is about 10 feet above the stove. The water is hot up to the point it enters the wall and then up in the attic where it exits the wall and makes the first 90 it is no longer hot. We tried bleeding it and draining the tank agan to try to force any air that might be in the line but no cigars. The plumber seems to think that the flow would not be impeded at the attic where it levels off with all the 90's but What are your thoughts???

[nick1234]

did you change tank. Use only old style tank with side connections (for heating) new tanks with top in do not work well  to knowledge. Cold water in to boiler must come from tank bottom or (side bottom old type tank) or there are flow problems.  If you must use new type tank use top heating element connection as hot in but you will have to make a fitting  for that. keep hot and cold runs separate if hot run heats cold run flow will also  be effected

enjoy

nick1234

[scottsAI]

Birdie4,

3 More 90's(at tank? 3/4 inch) and a horizontal run at the tank should not be a problem.

Any way to force flow? Like pressurizing the cold side?

Goal is to get hot water up to the tank, once.

How is the cold water added to the tank?

I strongly suspect air in the lines, even blockage. Assuming there are shutoffs in the system, check open!-)

If the firebox loop is always sloping up, then no place for air to accumulate...?

The water is hot up to the point it enters the wall and then up in the attic where it exits the wall and makes the first 90 it is no longer hot.

If none of above is the problem (air / blockage), must be a hot spot above the elbow in the wall. Very hot. Conduction can heat the water up to the elbow in the wall, not flow. Therefore loop flow is not getting started. A hotter spot is less dense, requires a driving force to bring it back down, if absent then loop not able to start.

If none of these work, will need pictures next! Heck send them anyways!

Have fun,

Scott.

[birdie4]

I'll try to get some pictures to send where do I send them?I'm not familiar with how to do that on this site.

Anyway, if I had a hot spot in the line wouldn't I feel it? It is very hot right over to the wall going up to the attic but in the attic it is cold at all the 90's so it seems to not be flowing up all the way and I don't really have a way to force it that I know of. I have not changed the tank from before only the 3 90's and the horizontal lines, remember before it had a slight rise out of the wall all the way to the tank and now it is level once it comes out of the attic wall. once the loop flow gets started will it continue or can it keep stopping on me? Thanks again I'll try to post some pictures.

[thirteen]

You might use a small level on the line going to the tank. It may look level but may not be. You might check all of the lines. If the line is long enough I would try and raise the tank just a little to get a slight angle upward. I am wondering if the lines are copper pipe or galvanized or black pipie.  Most will bend some to allow the tank to be raised. Could something have gotton into the lines or tank causeing a restriction. Also could the pipe inside the wall be grimped or bent. I had this problem years ago when I remodeled a garage wall. I had used a large nail to secure a 2x4 for a support on the wall cabinets.  After getting everything hung I pulled the board off but the nail remained. I just drove it into the wall stud not realizing that my pipes were behind it. The water did not run correctly in the shower. It always had low preasure on the hot side. I had driven the nail into the pipe. It took 1 1/2 years for the nail to leak and cause problems.  The lawn was always greener on that side of the house. Could your pipe have been bent or crimped sealing it up in the wall. Just some ideas

[thirteen]

if you have isolation valves in your lines could one of them be bad or broken or just not open all of the way? And some one else mentioned sweeping 90's instead of 90's that would help. There used to be an old rule that for every elbow you put in a line you add 8 - 10 feet of pipe restriction. It's been 25 years since I was told that so it may not be right. I have the best memory in the world it's just short. HA HA justy an idea to think about

[jimjjnn]

2 ea 45 degree fittings will workbetter than a 90 degree fitting as it allows a less restrictive flow