Thermo-syphon nightmare

Hi there,

My husband and I have a new Baker’s Choice wood stove and have attempted to hook up a thermo syphon system. We’ve tried for the last ten days and it keeps seeming to work and then turning cold. The only thing I can think of now is that we don’t have the tank high enough. We bought a pump to at least get it flowing for now, and the water is STILL cold coming through, even with the pump running.

Did we wreck our coil somehow?

Alana...you sound frustrated, but please do not be too hard on yourself. Thermo-siphon's are often talked about, but they are very difficult to actually get to work, much less work well, and much less reliably so. The first cars used thermo-siphon cooling systems and they were quickly abandoned for the reasons mentioned.

You have a pump, but it may be pushing the water around the coil too quickly. It takes time for heat transfer to take place. If you do not have one already, you may need a flow control valve, or just use a quarter turn ball valve and partially close it. You will have to figure out where the best spot is, but at some point you should be getting some heat.

Ideally you do not want to "shock" the system as it is called, and heat low and slow. That means ideally the water going back to the coil will be 15 degrees colder than what comes out of it. This is called Delta T. After a bit of time the water you are trying to heat will warm up.

Of course I am making a ton of assumptions here, and really need a lot more information like what you have for a set-up, and what you are trying to accomplish. I am really, really, really hoping you have a non-pressurized system though, and assume you do. There are some pretty big safety concerns if you do not.

In any case, welcome to Permies.

Alana could you sketch out the setup including where the water exits the tank, enters the stove, and returns to the tank. It would help if you dimensioned it as well. Usually a thermosiphon fail can be traced back to something straight forward. I do agree you get much better transfer with a pump. the 5 watt el sid always worked well for me. A standard ac pump would push it way too fast resulting in large amounts of luke warm water instead of half a tank of hot water, half a tank of cold. Some things to ponder. Another question I would ask is how many hours a day are you firing the stove? Thermosiphons work both ways so if you are doing short burns you would heat some water then it would bleed heat out when the stove cools...
Cheers,  David