Copper coil aorund the chimney connecting to the radiators

Hello everyone, I'm new to the forum.
I'm building my first RMH, and I'll try to make it all by the book, except one thing. I have central radiator system in the house, and I want to ut copper coil around the chymney pipe in the bench, and connect it to the two of the radiators on the next floor, without the tank. Can anyone tell me is it possible at all, without the tank? It isn't so big amount of water to heeat, two little radiators. I don't have to have really hot radiators, but it would be nice to use some of the heat for the floor. Here's the scheme. Would it explode or leak? What with the spreading of the water when warm/hot?

Thanks,
First Driver

Jacob Silver wrote:Hello everyone, I'm new to the forum.
I'm building my first RMH, and I'll try to make it all by the book, except one thing. I have central radiator system in the house, and I want to ut copper coil around the chymney pipe in the bench, and connect it to the two of the radiators on the next floor, without the tank. Can anyone tell me is it possible at all, without the tank? It isn't so big amount of water to heeat, two little radiators. I don't have to have really hot radiators, but it would be nice to use some of the heat for the floor. Here's the scheme. Would it explode or leak? What with the spreading of the water when warm/hot?

Thanks,
First Driver

Hi Jacob, welcome to permies!
First of all, the system you planned won't get warm enough to form steam so explosion is not an issue. But you need to do other things in order to get it to work and avoid rupture of the tubes.

What you need is an open system, with a small expansion container of say, half a gallon. So a mineral water bottle upside down with the bottom cut out is enough. That expansion tank need to be above all the other parts of the system and open. To slow evaporation pour some vegetable oil in.

In order to let the whole thing work without a pump you need to let the air come out by itself, so all the pipes should slope slightly upward to the radiator and the expansion bottle. A horizontal situated coil is no good here, a zig-zag in the top layer of the bench is a much better solution. Again, when there's only one spot where the water duct is sloping the wrong direction the contraption won't work, at all. Think your way up from the spot where the exchanger starts, in your sketch the closest to the heater itself. Every pipe, even the radiator has to go up from there.

Don't expect too much of it, I've used something similar for 30 years, a vertical zig-zag behind a small masonry heater. The radiator upstairs in the bathroom never has been hotter than hand warm although it did that 24/7 in winter time as long as the heater did burn every day for an hour or two. Also, your bench will be much cooler with this exchanger.

Hi Jacob, welcome to permies!

Going by your diagram, your system will thermosiphon heat up to your radiators... I haven't the math to comment on how effectively it will do so, especially since more quite a bit more info (distances, tubing sizes, temperature deltas, etc) would be needed.

The risk of overheating is a real one depending on where exactly you mean that collector coil to go, and with less water you'd be able to boil it that much more quickly. A pressure relief valve seems kind of important, but a low-tech alternative would be a system that is not sealed, and is inherently unpressurized...


Would this collector system tie in to the main heating system for the house? Or would you be removing these radiators from the central heat system to dedicate them to this system? If so, would this be switched with valves, or a permanent reassignment?


What sort of corrosion prevention measures are used in your existing radiator based system? How will you address this in the new system? This could impact the effectiveness of a thermosiphon by increasing viscosity; also, I wouldn't want antifreeze-laden water evaporating into my living space, in the case of an unsealed system.


One challenge of building a system like your diagram is the difficulty of experimentation. You don't know how the final system will behave until the bench is built... then, if you find it is getting too much or too little heat, what do you do? Dismantle the bench to adjust? No thanks! I'd suggest you plan on prototyping for a while with some sort of placeholder bench that allowed for easy access to, and adjustments of, the internal copper coil. Perhaps insulate around the chimney a little, but then use removable mass; big bags of something that you can lift in/out of a temporary wooden-framed bench?


An alternative that I personally would probably prefer would be to build the RMH, finish the bench, etc... then take on this project as an add-on, mounting the heat collecting coil around/near the barrel, rather than inside the mass. This would only work when the RMH was burning... but I am a bit skeptical that '2 little radiators' will make much of a temperature difference upstairs when the water inside is only being heated by the warmish mass, rather than the hot barrel. Of course it would be particularly important to consider the pressure issue here.


Another thing to consider is slight changes to airflow that may make a big difference to house comfort. Perhaps it is possible to add ventilation in the ceiling of the room with the RMH, to allow some of the hot air passage into the upper rooms directly?


Edit: and in the time it took me to say, "should do something, but I don't know how much", along comes an expert with first hand experience to give you real data!

Peter and Dillon, thank you very much for answers!

The radiators left from previous system, but I don't use them for 7 years, because I have wood heater, which is enough for good insulated house. So, I considered them to be isolated.
Your words gave me peace, I think I will give up from this – it is too much experimenting, complicated, copper pipe (22mm) isn't cheap, and results seems uncertain. As I have chimney (13cm) in the center of the house which heats a floor a little bit, which I will loose when I build RMH, I thought connecting radioators would replacing this loss.

Beside this, I had antifreeze in the system, and I don't know about the rust, since my system is shut for 7 years.
As life tought me, everything which seems complicated indicates on problems, much, much, bigger.
It is much simpler to bulid a little RMH on the floor or - as Dillon said – add the ventilation in the ceiling above the barrel, which seems to be more than enough.

Thanks a lot,
Jacob