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[pwdiver]

I had post earlier about a RTH8500D thermostat as I had stated not sure if possible would like to use the thermostat to control just the air handler for the heat and have the heatpump set as the backup heat not the Electric strip's if this is possible great, but I did not want 2 thermostat's like I had setup before. The current Honeywell RTH8500D is working great as it is setup now I just dont have backup heat if the boiler goes out. Any suggestion would be aprreciated.

[pwdiver]

Ive been in contact with Honeywell tech support on there thermostat's they say that none of there's will do what I want, I guess Ill have to canvas some of the other manufacture's about there product's I guess if I had to I could go back to 2 thermostat's but I dont want to.

[boilerman]

I'm surprised the Honeywell representative told you that. The Honeywell multi-stage YTH8320ZW100 has 3 heat and 2 cool source capabilities all on one programable thermostat which  should do what you want.

[pwdiver]

Thanks for the info I will look into that one.

[marty]

I want to chime in I went down this same road too (trying to eliminate second thermostat) and I also contacted Honeywell and was told no thermostats will do this.  boilerman-- have you actually used one of these thermostats in this setup?

[pwdiver]

My current Honeywell thermostat is a RTH8500D its working great for the boiler Im able to have this ramp the temp down at night and then back up in the morning. I f I have to Ill use this the way I currently have it and add another preferably Wifi for the heatpump like I had with the 2 wire thermostat I had previous.

[boilerman]

Here is how I've used the Honeywell 3 stage Thermostat I referred to. My dealer did not stock this thermostat, but ordered it from CB for me.
Just followed this wiring diagram illustration from the central boiler site. Here is the link to that diagram.
http://centralboiler.com/media/1106/c175.pdf

I purchased the DPDT relay switch (double pole double throw) from local heating supplier.

[schoppy]

I have a Honeywell programmable T-stat for my system but don't have the model number handy. It has multi stage and emergency heat capabilities. I used Geothermal for my primary heat source and LP for backup before I added my OWB (which was mainly for a new shed) but I decided to put all my heat loads on the OWB if I was going to keep burning wood. I didn't change anything regarding my T-stat with the exception of adding a strap on aquastat to my supply pipe set at 120 degrees which interrupts the 24 volt line to my geothermal contactor.

As long as the water temp is above 120 (or whatever temp you want) the T-stat cycles the furnace fan on as normal. It doesn't know or care that the geothermal isn't doing the heating. When the temp drops below 120 the contacts in the aquastat close and the geothermal kicks back in. Has worked flawlessly for me.

[RSI]

My current Honeywell thermostat is a RTH8500D its working great for the boiler Im able to have this ramp the temp down at night and then back up in the morning. I f I have to Ill use this the way I currently have it and add another preferably Wifi for the heatpump like I had with the 2 wire thermostat I had previous.

The central boiler diagram that Boilerman posted with the summer / winter switch will fix the problem I mention a few days about screwing up the a/c. If you are using the programming and changing the temp a lot, it may start running your heatpump due to the temp differential between primary and secondary temps being exceeded. If you used an aquastat like Schoppy you would not have that happen.

[pwdiver]

Thanks for the info I have more to think about now, thanks for the diagram Boilerman

[mlappin]

The nest can also be set for three heating sources, just use the * terminal for your third heat source. On mine * is used for the humidifier. From the menu you can also set G to be on for a call for heat with a heat pump.

[RSI]

My brother called me today and wanted to get a single thermostat working. He has a gas furnace so a little simpler than a heat pump.

To get it to work the way he wanted, we had to go with this wiring: (Hopefully the columns line up below)
thermostat     furnace
C                     C
RH                   RH
Y                     G
O/B                 Y   (thermostat to energize on cooling)
W1                 W

The reason we used this wiring was because he wanted to be able to manually turn on the gas heat. Using W1 and W2 it appeared to work but would have to hit the differential setting and he wanted to keep the hour delay setting before the gas furnace comes on.

It may be possible  to get a heatpump to work by using 2 stage heat pump settings. I think it would require adding a relay and may not have an option to turn on the heat pump manually without raising the thermostat temp.

[mlappin]

My brother called me today and wanted to get a single thermostat working. He has a gas furnace so a little simpler than a heat pump.

To get it to work the way he wanted, we had to go with this wiring: (Hopefully the columns line up below)
thermostat     furnace
C                     C
RH                   RH
Y                     G
O/B                 Y   (thermostat to energize on cooling)
W1                 W

The reason we used this wiring was because he wanted to be able to manually turn on the gas heat. Using W1 and W2 it appeared to work but would have to hit the differential setting and he wanted to keep the hour delay setting before the gas furnace comes on.

It may be possible  to get a heatpump to work by using 2 stage heat pump settings. I think it would require adding a relay and may not have an option to turn on the heat pump manually without raising the thermostat temp.

I quite farting around with it, getting the Nest fooled into thinking my wood heat was a heat pump that is. Just about time I think I had it fooled it would still kick the gas furnace on just to be contrary. Installed a line aqua stat and took the W wire from the nest to the common on the stat, above 130 and the W gets connected to the G terminal on the furnace, below 130 the W wire connects to the W wire on the furnace. I may just manually adjust the aqua stat once in a great while to exercise the gas furnace once in awhile.

One distinct advantage to the two thermostat system is by a bit of programming I could have the gas furnace run once a day even if only for 5 minutes.

[pwdiver]

Thanks for all of this info, I even contacted Nest and got a reply saying that there thermostat would not do what I wanted. Im still looking

[mlappin]

Thanks for all of this info, I even contacted Nest and got a reply saying that there thermostat would not do what I wanted. Im still looking

With the clever use of a relay or two and maybe an aqua stat it should work, Nest meant most likely directly out of the box it won’t do what you want.

I’m not overly impressed with who I spoke to at Nest or her supervisor about troubleshooting why I had an intermittent use of my humidifier. No matter how many times I explained normally my Orange wire which is connected to a relay to close the for the humidifier to kick on is hooked to the * on the Nest and it won’t do nothing now and hasn’t for a week, but if I disconnect the White wire going to the W connection and hook my humidifier wire to the W connection and turn the thermostat up, then the humidifier would kick on.

Took 15 minutes to get em to send me a new back plate.