HVAC: What's best for cold climates?

[Harvey]

A two stage thermostat will kick in backup heat with a temperature 2° lower than what it’s set for. If you walk into a cold house and bump up the temperature a conventionally programmed thermostat will automatically turn on backup.
That’s fine for a regular heat pump but bad if you have a gas furnace as the furnace temperature is now entering the heat pump coil at a much higher temperature than returning room air, No Bueno!!!
I prefer the Honeywell Vision Pro 8000 thermostats as they can be programmed for that scenario. They have terminals for an outdoor sensor that can decide which heat you want. Say heat pump above 40° while restricting furnace operation to only heat pump defrost cycle.

In the meantime I would suggest that you run the system using emergency heat setting ( furnace) until you can fix it.

I'm not sure i actually have a dual fuel system. I think I have two separate systems. The propane runs a hydronic (radiator) system and the heat pump is forced air.

Does that matter?

 

[Sbob]

I'm not sure i actually have a dual fuel system. I think I have two separate systems. The propane runs a hydronic (radiator) system and the heat pump is forced air.

Does that matter?

I was assuming you had a gas furnace tied in with the heat pump. People sometimes interchange furnace and boiler, you do not have a duel fuel system. Boilers are used with hydronic baseboard systems, but can be used with a hydronic coil in the ductwork for backup heat. Totally fine with a heat pump when downstream of the heat pump coil. Curious though are they on one thermostat or two?

 

[Harvey]

So you are saying we aren't making a mistake by running both?

Curious though are they on one thermostat or two?

This is the question of the hour. They wired for two. Apparently these are "construction thermostats" that will be replaced with Eco Bee (?) at the end.

I never imagined two thermostats. We have one thermostat in NJ and it works well. But it looks like they were planning on putting in two.

They told me I could have one or two thermostats, my choice. But NOONE can seem to tell me pros and cons of each method.

Ideally I'd like the radiant in the basement floor to run at a low level, all winter. I think.

I planned to LEARN by experimentation, what the ideal cutover is (10, 15, 20 degrees?). I assume to make the cutover automatic, I need one thermostat?

What do you think?

BTW @Sbob I really appreciate your expertise and help (and patience!) with this.

 

[Sbob]

So you are saying we aren't making a mistake by running both?


This is the question of the hour. They wired for two. Apparently these are "construction thermostats" that will be replaced with Eco Bee (?) at the end.

I never imagined two thermostats. We have one thermostat in NJ and it works well. But it looks like they were planning on putting in two.

They told me I could have one or two thermostats, my choice. But NOONE can seem to tell me pros and cons of each method.

Ideally I'd like the radiant in the basement floor to run at a low level, all winter. I think.

I planned to LEARN by experimentation, what the ideal cutover is (10, 15, 20 degrees?). I assume to make the cutover automatic, I need one thermostat?

What do you think?

BTW @Sbob I really appreciate your expertise and help (and patience!) with this.

I personally like having some redundancy by keeping the two systems separate. I have a saying “They don’t make junk like they used to." Stuff breaks more quickly than it used to. The efficiency of equipment is much higher but more vulnerable to power surges. It pains me to replace old mercury thermostats that work for 50yrs with something that will quit after 6 yrs.

The downside to two thermostats is you can have conflicting operations, Heat running while the AC is running.
It just takes some mindfulness but it’s not the end of the world just waist some energy.

Basement? 55-60? Just enough to keep moisture out.

Keep an extra thermostat in the house lol. And maybe some boiler parts (igniter, flame sensor)

 

[Harvey]

If you keep it separate how do you manage the cutover from heat pump to propane?

Manually I assume, but how?

 

[Sbob]

If you keep it separate how do you manage the cutover from heat pump to propane?

Manually I assume, but how?

Not necessarily, they can work together while keeping the power supply separate.A quick wiring sketch. You may have some differences but adding an outdoor thermostat to the heat pump and connecting a relay to the wiring to operate the boiler.
You probably have some zones attached to the boiler that may complicate things a little but it’s doable.

 

[Milo Maltbie]

All heat pumps in cold climates have always had a back up furnace for cold days, and it's all controlled automatically. Gas furnace back up systems are relatively new but they're controlled from the same thermostat as the heat pump.
Ideally you want your system controlled from one thermostat, but with a redundant system you will not find in off the shelf plug and play solution. You probably have an electric furnace with your heat pump, and you could disconnect that, which maybe only means pulling an internal fuse. OTOH you may need that furnace to de-ice the outdoor heat exchangers.
You could use an outdoor thermostat to switch from heat pump to gas, with separate inside thermostats for the gas and HP. Unless LPG is way more expensive, you could just run the boiler all winter, or at least in the coldest months. That might be the most comfortable solution. A another possibility might be to modify the HP controls to shut down completely whenever it would otherwise start the back up furnace, and set the gas thermostat a couple of degrees lower that the heat pump. Or you could design a control system that switches based on current electric and gas prices. Good luck with that.
What you really want to avoid is running the boiler for heat and the HP for cooling at the same time. That's more common than you would think in large buildings, especially in the fall. Whatever you do, your control system needs to be simple to use. If you have two thermostats someone is going to set them to work against each other in the most expensive way possible.

mm

 

[Campgottagopee]

BTW @Sbob I really appreciate your expertise and help (and patience!) with this.

Me too!
Thanks @Sbob

 

[Campgottagopee]

I personally like having some redundancy by keeping the two systems separate. I have a saying “They don’t make junk like they used to." Stuff breaks more quickly than it used to. The efficiency of equipment is much higher but more vulnerable to power surges. It pains me to replace old mercury thermostats that work for 50yrs with something that will quit after 6 yrs.

Truer words have never been spoken. And I don't think it matters what industry a person is talking about. Junk used to be made to be fixed, now junk is made to be thrown out and replaced with something even higher on the junk scale.

 

[Sbob]

All heat pumps in cold climates have always had a back up furnace for cold days, and it's all controlled automatically. Gas furnace back up systems are relatively new but they're controlled from the same thermostat as the heat pump.
Ideally you want your system controlled from one thermostat, but with a redundant system you will not find in off the shelf plug and play solution. You probably have an electric furnace with your heat pump, and you could disconnect that, which maybe only means pulling an internal fuse. OTOH you may need that furnace to de-ice the outdoor heat exchangers.
You could use an outdoor thermostat to switch from heat pump to gas, with separate inside thermostats for the gas and HP. Unless LPG is way more expensive, you could just run the boiler all winter, or at least in the coldest months. That might be the most comfortable solution. A another possibility might be to modify the HP controls to shut down completely whenever it would otherwise start the back up furnace, and set the gas thermostat a couple of degrees lower that the heat pump. Or you could design a control system that switches based on current electric and gas prices. Good luck with that.
What you really want to avoid is running the boiler for heat and the HP for cooling at the same time. That's more common than you would think in large buildings, especially in the fall. Whatever you do, your control system needs to be simple to use. If you have two thermostats someone is going to set them to work against each other in the most expensive way possible.

mm

Good advice

Having a dual fuel setup with a heat pump set for outdoor low ambient shutdown has some risks. Reminds me of a humorous story , my friend called saying his heat pump wasn’t running. We had lots of cold and snow for an extended time then a quick warm up. The snow had accumulated on the fan blades so when it started it was severely out of balance. The bolts came off the bracket and it ended up wobbling so badly that the whole outside unit came off its base and literally looked like it was hit by a truck lol. It was Doa ….