About a year ago I joined in a thread, which is now locked, called:
Fully Modulating Furnace, Regular or Communicating thermostat?
Its purpose (when it started) was to answer the question whether one should use a regular or a communication thermostat with a fully modulating furnace. I just then bought a York 100K fully modulating furnace and wanted to know if the "future" communicating thermostat from York would help keep my house in California an a rather constant temp during the day.
What we found out when we were able to talk with the designers of the controller at JCI was that setbacks completely messed up the controllers algorithm and it had to "start all over" every time a setback happened. The long and the short of it is that with setbacks on a normal - or even on their communicating - thermostat causes the system to start at low burn levels, and then quickly escalate up to max burn within 3-8 minutes after the first heat call after a setback completes. And this repeats for each new setback.
I found a way to program the York controller with a PIC chip to always stay in diagnostics mode and set the controller at 30% burn rate and low fan condition. This lasts only for 120 before the controller does an automatic reset and starts over. The PIC chip sees this happening and puts the controller back into diagnostic mode for another 120 minutes. This is a very primative and dumb way to get low furnace burn, BUT it does work and has no problems with 4 setbacks-a-day. I can share with anyone who wants how to wire and program the PIC, but it probably voids a warantee and you need a PIC programmer (which can be purchased for under 6 McDonalds burgers).
MY QUESTION IS: has anyone found a thermostat that will keep the York fully modulating furnace at a fixed burn rate? Is so, where can it be found, and does it allow you to set the fan rates as well?
POSTSCRIPT: I got "tagged" by the moderator a number of times for not "setting it and forgetting it". A nice mantra, but very costly. I have used the furnace for almost 1 year now. I live in Silicon Valley where the winter temperatures only get below freezing about 8 times a year and for only a few hours when it does occur. I need a furnace for only 6-8 months a year. I kept track of the daily temperatures over the last winter and used PG&G's SmartMeter to measure gas usage each day. I kept the furnace at 68-70 deg F during the day and set it back to 60 deg during the nights. Slightly different timing and temperatures for the weekends, but all are typical. By using setbacks from 11PM until 8AM during the weekdays (and almost the same for weekends), I saved over $600 in just gas costs. There would be a little more for electrical savings from decreased fan use. This just amplifys why the Federal Government MANDATES that all new public housing must have programmable thermostats: they save huge amounts of money and natural gas. So setbacks should be part of every new furnace.