Our upstairs Lennox furnace always fires off on high stage whenever the fan setting on the thermostat is set to "on" and then switches to low stage 15-20 seconds after. We don't usually keep the blower always on all the time but we decided to try out the fan on mode. The furnace operates normal with the fan set to "auto". Our thermostat is NOT wired for 2 stage.
Is it normal for the furnace to perform like this with the blower circulating air nonstop? Thanks.