Add-on Wood Furnace Help!!

[thecontrolguy]

Folks;

As usual, I stand in awe of the combined wisdom and experience on this forum. Hope to tap some of it.

The situation is that I am replacing the (awful!) oil furnace that I've McGyver'd along for the last few years with a new electric furnace. (Broan 21B15M) The reasoning is that here in B.C. the electricity is (mostly) hydro generated (aka renewable) and it is an easily maintainable back-up. Also, I need a blower to move the air through my big RSF add-on wood furnace. AND, I hate the continuous stank of oil in the house

Now, the pickle is that I have a small electric sub-panel that is mechanically interlocked to allow me to power certain loads with either the regular hydro power or my 6500 VA genset. (all legally installed) It is limited by the 30 amp, 2-pole feed and so I cannot power the electric furnace from this panel. Which means, I can't get heat during a power failure. Actually, if the power fails while the wood furnace is stoked, the ducting gets too hot to touch!! Yikes!! So I need a blower.

Therefore I (conceptually) figured out how to run a dedicated 240 vac circuit from the essential panel and add a relay to disable the heating elements, power the low-voltage controls and thermostat, and power the blower if needed by the wood furnace. However, this kills the factory warranty, inspection approvals, and CSA / ULC approvals for modifying a factory approved device. Has anyone encountered this problem and figured out a legal and safe work-around that will keep the insurance valid (and the wife happy!)??????

Thanks for ANY help. Cheers.

 

[kabbott]

When running off the genset could you use a relay to cut the thermostat wire, and just run in fan on manual mode.?
In other words use relays in the low voltage TT lines only.

 

[thecontrolguy]

When running off the genset could you use a relay to cut the thermostat wire, and just run in fan on manual mode.?
In other words use relays in the low voltage TT lines only.

Thanks for the thought kabbott. I not only need to break the call for heat to the electric furnace during the time period the house is on essential power (genset), I also need to get power into the furnace for the fan, that is normally powered from the high-current feed (100amp, 240 vac) from the normal power electrical panel. This is where the local inspection branch gets all hinky.

 

[smokinj]

When running off the genset could you use a relay to cut the thermostat wire, and just run in fan on manual mode.?
In other words use relays in the low voltage TT lines only.

Thanks for the thought kabbott. I not only need to break the call for heat to the electric furnace during the time period the house is on essential power (genset), I also need to get power into the furnace for the fan, that is normally powered from the high-current feed (100amp, 240 vac) from the normal power electrical panel. This is where the local inspection branch gets all hinky.

dont your thermostat have a fan only setting?

 

[Gooserider]

When running off the genset could you use a relay to cut the thermostat wire, and just run in fan on manual mode.?
In other words use relays in the low voltage TT lines only.

Thanks for the thought kabbott. I not only need to break the call for heat to the electric furnace during the time period the house is on essential power (genset), I also need to get power into the furnace for the fan, that is normally powered from the high-current feed (100amp, 240 vac) from the normal power electrical panel. This is where the local inspection branch gets all hinky.

dont your thermostat have a fan only setting?

It probably does, but I think I see the problem - regardless of what the thermostat turns on, there is still only ONE feed line to the furnace, namely the same line that feeds the elements, and which is locked out when on the genset - IOW, the thermostat can turn the fan on, but the fan won't have AC power...

The only real solution is to have seperate AC lines for the elements and the fan, running from different panels so that the fan power could still be live, however this doesn't seem to be something the OP can get past the inspectors...

I only see two solutions - one is to hand the problem to the inspector types asking them how to rewire the existing unit in a way that they will be happy with, or to come up with a second "emergency only" blower for the wood furnace and hang that off of the wood unit somehow (which would also have to keep the inspectors happy)

Gooserider

 

[thecontrolguy]

It probably does, but I think I see the problem - regardless of what the thermostat turns on, there is still only ONE feed line to the furnace, namely the same line that feeds the elements, and which is locked out when on the genset - IOW, the thermostat can turn the fan on, but the fan won't have AC power...

The only real solution is to have seperate AC lines for the elements and the fan, running from different panels so that the fan power could still be live, however this doesn't seem to be something the OP can get past the inspectors...

I only see two solutions - one is to hand the problem to the inspector types asking them how to rewire the existing unit in a way that they will be happy with, or to come up with a second "emergency only" blower for the wood furnace and hang that off of the wood unit somehow (which would also have to keep the inspectors happy)

Gooserider[/quote]

Thanks, Goose. Your point is well taken, btu ends up exactly where I stand. The "Safety Authority" around here is all about putting the requirement of liability on the contractor(s) and not getting involved in this type of thing. Therefore, no help from the electrical inspectors. Electrical code in Canada gets hinky when a device is powered with two separate sources and also any sort of modification of an approved device without the factory OK. I am still waiting to hear from Broan, but may end up having to take matters into my own hands, so to speak.

Too bad for me. Thanks anyway, though.

 

[kabbott]

This could be done very easily with a relay/contactor/transfer switch whatever.... something triple pole-double throw..... that switches from on power source to the
other and cuts the TT line to the unit so the elements can't turn on(just the blower).problem is getting the "MAN" to approve it and if it is a hefty load you will
end up with more money invested than you would like i am sure.

I myself have a 20kw 12 wire genset that I wanted to have auto switchover, that was until I priced the auto transfer switch for twin 150 amp services.YIKES

I took the cheap way out and went with mechanical interlock for both panels. Anyway I know this can get expensive quickly.
Maybe the answer IS a second blower unit?????
I don't have any better ideas...sorry

kris