Log Wood Burner

[sasik]

My costumer have a log wood burner with five radiators and one hot water cylinder. Four out of the five rads are pumped and the hot water cylinder and one rad (the heat leak) are working via convection. My question is, can I change this system from a partly pumped system to a fully pumped system by simply connecting the two separate circuits together? and if so will it work or it will cause more problems in the future?

Thanks sasi

 

[Plouasne]

Have you ever seen a log boiler "dancing" because it was burning fast and the pump failed, the water was literally boiling hard inside the boiler, not a pretty sight to see, its enough to want you to change your knickers

My advice to you would be to have the pump on the return and fit a venturi "Tee" also known as an injector "Tee", just after the pump to pick up the cylinder return, this will help you have a gravity circulation if the pump fails or there's a power cut, with the pump running it will help to "drag" the cylinder heating water around the cylinder circuit a bit faster

 

[migoplumber]

plouasne's advice is ok. however i would add that solid fuel is probably more dangerous than unvented, if you are even slightly unsure of the controls involved (as your question implies) then pass it on to somebody who knows and add your 10%
you can assist and learn and the client will remain safe

good luck

 

[sasik]

Hi Plouasne

I can see your point, but I will try to refine my system a little bit more. I have one set of flow and return out of the log burner for the rads (pump on the return) and one set of flow and return for the hot water cylinder + heat leak rad (no pump). I want to connect the "heat leak" rad to the pumped circuit but still keep it as the heat leak source for the log burner. So if the pump wouldn't work for some reason the flow and return for the cylinder will be still open. The heat leak rad is just tee off the cylinder. Please let me know if it make sense to you and if so will it be safe (the last thing I want to see is a log burner doing a break-dance in my costumer living room!)

 

[migoplumber]

sasik, your cylinder would be an ideal "heat leak" as you call it, but imagine your electrical failure, no pumps, no zone valves working. 130 degree steam "heat sinking" into your cylinder, the water inside the cylinder will become unhappy angry water turning itself into steam as well. guard that thought befor you continue.
i am trying to give you good advice!!

 

[Plouasne]

Sasik,

This is the way I would go about it,

1) Cold feed from expansion tank direct to boiler

2) Central heating flow from the boiler

3) Hot flow from boiler to Cylinder, "Tee" of with a sweep "Tee" to cylinder continue to rise to expansion tank as the open vent pipe (6" plus 1/2" per foot difference between bottom of boiler and the water line in the expansion tank before turn over of the open vent pipe), also "Tee" off with a sweep "Tee" at high level and drop to heat leak rad (it goes without saying that there should be no valves on the heat leak rad)

4) Return from cylinder with a sweep "Tee" to pick up the heat leak rad

5) The cylinder return is connected just after the pump, on the central heating return, with a venturi or injector "Tee", the cylinder return must be connected on the branch of the venturi "Tee"

The Idea of this is that the pump will create a pressure drop in the venturi "Tee", which will help to circulate the cylinder side of the heating water, around the system, and at the same time allow a free gravity circulation, if the pump is not working

Pipe sizing, including expansion tank size, and expansion tank overflow size, should be designed, failing this to be taken from a recognised source of information, for example the Chartered Institute of Plumbers and Heating Engineers, Design Guide, and also follow the boiler makers instructions with regard to a pipe 'stat to control the pump, if applicable

 

[sasik]

Hi plouasne and migoplumber, thank you very much for your comprehensive advice about that mater.

thanks sasi