Control assistance

allenn · September 11

I have a gas furnace with a thermostat that controls it on one zone. I am looking to add a separate duct to draw heat from another area of a house where there is a woodstove. I am looking to tie the new duct into my existing return to have it distribute it into my home. I would like to add a 2nd thermostat to my furnace to kick on a fan only option when the room with the woodstove gets to a very temperature in order to get the heat out of that room. Any thoughts?

mattmia2 · September 11

Just connect it in parallel with r and g on the furnace

Jamie Hall · September 12

Do you want to activate a fan in the new return duct from the wood stove room to help move air into the rest of the system, or turn on the existing fan in your existing furnace to just increase circulation in the existing system with some heat being pulled from the room with the stove?

Two very different problems.

If you have that new duct, by far the simplest approach will be to put a fan in that duct and a 120 volt thermostat powering that fan in the room with the stove. This will move air into the existing return. Some of that will blow back out the other returns in the house. Some of it — probably a smaller fraction — will move through the furnace filters and appear at the heating registers.

Or… you could have that new duct with no fan, and a thermostat in the stove room to turn on the fan only option on your furnace — assuming that the furnace control system has such an option. Some do. Some don't. That will draw some air from the stove room, just like any other return would, and most of the air from the rest of the returns. Not sure how much good that will do.

Or, if your boiler control does have a fan only control input, you could have a thermostat in the stove room which activated that, as above, and through a relay activate a new fan in the new duct. This would get more of the return air from the stove room and less from the rest of the house.

EdTheHeaterMan · October 2

This might work for you

Screenshot 2024-10-02 at 12.21.16 AM.png

SuperTech · October 2

Wouldn't adding that return have the potential to negatively affect the draft on the chimney for the wood stove? If you are pulling more air out of the room then the furnace fan is adding to the room I can see it causing a back draft problem.

EdTheHeaterMan · October 2

Back draft may happen ONLY if that new duct causes a negative pressure in the room. So if the wood stove room has the doors shut and any supply register are sealed off, then that room may have a negative pressure. However I see the wood stove room as one that has the entry way from the rest of the house always open, with an open floor plan to the rest of the house. There is most likely no closable door to that space. But that is just my thoughts on that matter. @SuperTech, you are correct to point that out, just in case I am wrong about my floor plan assumptions.

mattmia2 · October 2

Regardless of if it will backdraft the appliance or not I think a return in the same room as natural draft equipment is prohibited.

EBEBRATT-Ed · October 2

Use a Rib RIBU1C relay. Wire the NO (orange & blue wire) contacts to R & G on the furnace. Take 24 volts from the furnace transformer and run the common 24 volt wire to the rib relay coil (yellow/white wire). Run the other 24 volt wire to R on the wood stove thermostat and a wire from W on the thermostat to the other Rib relay coil wire white/blue wire

EdTheHeaterMan · October 2

https://forum.heatinghelp.com/discussion/comment/1812711#Comment_1812711

You probably want to use R and Y on the wood stove thermostat Ed. You want to bring the system ON with temperature rise. R and W will bring the system ON with temperature fall. I made that mistake on the first diagram above, before I posted it, then corrected it before posting.

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