'I paraphrase, "the furnace should not run much longer than the 5 minutes at a time because it was hard on the equipment especially the burner." He also said that it was more efficient to run the furnace more frequenty but for shorter periods.
What do you make of that? It seems that the constant cycling on and off would be worse. Opinions?
ME: If Honneywell told you this, then, im mighty surprised ; Running the furnace more frequently for shorter periods...might afford you the greatest amount of comfort, BUT, it will come at an expense --- both to the equipment life and fuel consumption. What you want to do , is, to experiment with the cycle rate of the thermostat until you achieve close to a 2 degree f. drop in room temp. before the next furnace cycle starts ; whatever a 2 degree F. drop equates to in terms of 'cycles per hour' , is where you should set it. This way, youll achieve satisfactory comfort and not short cycle the furnace excessively. (Bear in mind, that, you may need to make a periodic adjustment to this as the outside temp. gets significantly colder/warmer thruout the winter ).
1. As I mentioned in my first post I have the Vision PRO that is set for 4 cycles per hour for the 1st stage of heat. The installation manual gives a range of typical cycles per hour based on the type of system you have. It recommends
1 cycle for steam, 3 cycles for hot water or 90% forced air system, 5 cycles for forced air systems under 90% and 9 cycles for electric forced air systems.
Does anyone know why 3 cycles is recommended for 90%AFUE and above and 5 is recommended for below 90%?
2. Why would you have to muck about with the number of cycles when the outside temperature gets warmer or colder?
I wouldn't tweak with the cycle rate per hour based upon outdoor temp changes. I'd find a cycle rate that works well for normal cold weather and leave it at that.
On my own VisionPro I've lowered the cycle rate for my Trane 80% from 5 CPH to 4. This gives a longer interval between calls for heat and allows for a slightly higher temp drop before the stat calls for heat, which translates to slightly longer run times for the furnace. That in turn means more comfort and less stress on the equipment, along with fuel savings as the furnace isn't constantly bumping on and off.
The previous owners of our house oversized the furnace and a/c, anticipating finishing out a garage conversion, which they never did but I've since done. Even so, after running a heat calc on the house I'm a ton oversized in cooling and could do fine with a 50 vs. a 60k BTU furnace. Just goes to show the size-by-thumb method is bogus.
Building Physics Rule #1: Hot flows to cold.
Building Physics Rule #2: Higher air pressure moves toward lower air pressure
Building Physics Rule #3: Higher moisture concentration moves toward lower moisture concentration.
I also have a Trane 80% 2stage VS and the Vision pro. I had the cycle rate lowered from 5 to 4 in November and so far everything seems to be ok.
I was just wondering why the Trane installation sheets would recommend 3 cycles for 90% or better, but 5 cycles for below 90%?
What kind of difference does this cause because the efficiency is lower?
Last week the temp was in the single digits and I had good long run times. And sometimes less than 4 cycles per hour. This week it is in the mid to upper 40’s. The system runs a bit to recover from set back, and then may not run for 5 or 6 hours, so I really didn’t see the need to move the cycle rate all the time. With the VS blower I keep it set to “on” during the heat periods to distribute the heat from the upper floors throughout the house, so maybe that accounts for the long off times when the weather is mild.
I have read a release from Honeywell that shows that their thermostats use tri-ads(voltage stealing) boards and they are having problems with furnace boards. To use these thermostats you needed a resister accross the terminals.
I just started using the White Rodger that didnot use that type of board.