> On Aug 31, 2021, at 07:15 , Mark Tinka <mark@tinka.africa> wrote:
>
>
>
> On 8/31/21 16:06, Mel Beckman wrote:
>
>> I think you’re forgetting about the all-important blower fan in a gas-fired
>> furnace.
>
> Well, I was referring to a pure electric furnace, not one that uses a blower
> over a gas-fired one :-).
>
> In that case, the blower is not a major draw on power.
>
> But again, we don't have those things here, so :-).
>
>
>> 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.
>
> Makes sense.
>
> Does this, then, mean that if the blower itself were to fail, the gas burner
> would not light?
Yes… Sort of.
In most cases, the burner lights off ever so slightly before the blower starts
up (if you’ve ever tried to light a campfire in high wind, you’ll understand
why).
However, if the blower fails to start producing wind on demand, the gas to the
burner will be shutoff and the system will go into an error mode requiring a
reboot or service intervention.
Of course a reboot without correcting the blower issue probably results in a
repeat of the process.
Owen
