To stage 10kw, someone would have to redo the controls on the heat kit. Usually it would take 15kw and up to stage.
Jim, Rheem hasn't replaced demand with time in ages. That was the way they replaced the Ranco DD1 board in the early 90s. Now it is 100% demand and replaced that way. I don't think ICP has been demand in some time either. They used the DDL board Rheem used for a short time. That board was unreliable. They went back to timer, Rheem found a different vendor with a more reliable board. I assume York has a lot of demand boards still. Lennox/Allied in select high end units. Actually Allied in the 16 SEER but not the 18 SEER. I think they needed it to get a HSPF target. Obviously Trane has been demand forever. Oh, and Nordyne on high end too. Still want to replace my time board with the board out of the FT4BF. Looks like it will work!