On 8/31/21 07:06, Mel Beckman wrote:
Mark,
I think you’re forgetting about the all-important blower fan in a gas-fired
furnace.
We're *really* getting in the weeds here. A single note to the list
about not backfeeding has really blown up.
That said, the reason the code requires furnaces to be hardwired is to ensure
that the blower interlock system can’t be bypassed. An electrical interlock
ties a heat recover ventilator to circulation air blower operation of a
forced-air furnace system. This ensure that the blower circulates supply and
return air within the structure. A plug-in power source leads to the
possibility that this interlock could be accidentally defeated, resulting in an
overheat within the flame box.
This doesn't compute. In a conventional forced air furnace the 24V
transformer operating the thermostat, logic, and gas valve is powered by
the same electrical source as the blower. In the event of someone
unplugging the furnace, or for that matter a power failure, the gas
valve will close when the power disappears.
Yes, there are old-school pilot light thermocouple-powered gas valves in
wall and floor heaters that require no electricity at all. They rely on
convection to distribute the heat, not a blower.
--
Jay Hennigan - j...@west.net
Network Engineering - CCIE #7880
503 897-8550 - WB6RDV
