Heat Pump w/ Gas Boiler Baseboard Heat Backup

JustinS

I am considering replacing my existing AC single-stage system with a variable capacity heat pump and am trying to determine if I will be able to use my existing gas boiler => hot water baseboard heating system as a backup.

The various installers who have provided quotes have talked about a "hybrid" system which would seem to indicate that it is possible; however, I am struggling to understand the specifics.

I have asked them but given the heat/humidity of late in Massachusetts, my interaction with them has been limited.

I have been proposed Lennox EL18XPV and American Standard Platinum 20

fentonc

You could just manually turn on your boiler and turn off the heat pump when you feel like it's not keeping up (or you've figured out the cross-over point where it would be cheaper / more efficient to operate). Alternatively, you could just set the thermostat for the boiler very slightly lower than the heat pump is set at, so that it would automatically kick in. They also make thermostats that can switch over to an auxiliary heat source if the main one can't maintain the temp after a certain point.

JustinS

fentonc said:

You could just manually turn on your boiler and turn off the heat pump when you feel like it's not keeping up (or you've figured out the cross-over point where it would be cheaper / more efficient to operate). Alternatively, you could just set the thermostat for the boiler very slightly lower than the heat pump is set at, so that it would automatically kick in. They also make thermostats that can switch over to an auxiliary heat source if the main one can't maintain the temp after a certain point.

Hi, thanks for the feedback.

Looking at the Lennox S30 and the American Standard XL1050 (proposed thermostats), it seems like both can control the heat pump and an auxiliary backup heat source. What's not clear to me is if this includes a conventional hot water gas boiler. They mostly seem to talk about gas furnaces and not much about gas boilers. Both are controlled via 24VAC so I'm not sure why it would be an issue.

My preference would be a single thermostat for the whole system like the S30 or XL1050.

pecmsg

Probably set up the T-stat determines when to use the
heat pump
back up
and emergency heat. 

JustinS

pecmsg said:

Probably set up the T-stat determines when to use the
heat pump
back up
and emergency heat. 

Ideally, yes... any reason why a conventional gas furnace would be supported and a gas boiler wouldn't be?

Jamie Hall

JustinS said:

pecmsg said:

Probably set up the T-stat determines when to use the
heat pump
back up
and emergency heat. 

Ideally, yes... any reason why a conventional gas furnace would be supported and a gas boiler wouldn't be?

Not really. The two normally are set to a different number of cycles per hour, so if you can't set that for the boiler that could be a bit of a nuisance, if not a problem.

JustinS

Jamie Hall said:

JustinS said:

pecmsg said:

Probably set up the T-stat determines when to use the
heat pump
back up
and emergency heat. 

Ideally, yes... any reason why a conventional gas furnace would be supported and a gas boiler wouldn't be?

Not really. The two normally are set to a different number of cycles per hour, so if you can't set that for the boiler that could be a bit of a nuisance, if not a problem.

I'm not 100% sure but I think that the CPH settings for the XL1050 and S30 are for the heat pump.

WMno57

JustinS said:

My preference would be a single thermostat for the whole system like the S30 or XL1050.

Then you have a single point of failure, the thermostat. Redundancy. Two stats, two fuels, two heating appliances. Might save you a lot of grief if you go away for a vacation in in the winter.

JustinS

WMno57 said:

JustinS said:

My preference would be a single thermostat for the whole system like the S30 or XL1050.

Then you have a single point of failure, the thermostat. Redundancy. Two stats, two fuels, two heating appliances. Might save you a lot of grief if you go away for a vacation in in the winter.

Hmmmm, good point...

WMno57

Thermostats are pretty reliable. The batteries inside them, terrible. Happened to me last winter, came home to a 40 degree house.

Jamie Hall

Is this where I mutter about the good old reliable T87?

JustinS

WMno57 said:

Thermostats are pretty reliable. The batteries inside them, terrible. Happened to me last winter, came home to a 40 degree house.

Thankfully, my thermostats aren't battery powered :-)

HVACNUT

I'm not familiar with the thermostats you listed, but staging is done though it. As long as everything is wired correctly.
Have you looked into 2 stage heat pumps? You could potentially have 2 cooling stages and 3 heat, with stage 3 being the boiler. That's pretty much my plan when it's time to replace my AC. I'm swinging between 2 stage and inverter. I'm leaning towards the KISS method.

pecmsg

WMno57 said:

JustinS said:

My preference would be a single thermostat for the whole system like the S30 or XL1050.

Then you have a single point of failure, the thermostat. Redundancy. Two stats, two fuels, two heating appliances. Might save you a lot of grief if you go away for a vacation in in the winter.

Since installing a heat pump and the controls are powered off the air handler the old T87 is no in the boiler room wired into the boiler as a back up!

JustinS

HVACNUT said:

I'm not familiar with the thermostats you listed, but staging is done though it. As long as everything is wired correctly.
Have you looked into 2 stage heat pumps? You could potentially have 2 cooling stages and 3 heat, with stage 3 being the boiler. That's pretty much my plan when it's time to replace my AC. I'm swinging between 2 stage and inverter. I'm leaning towards the KISS method.

I hadn't really considered 2 stage heat pumps, both installers started with variable capacity ones.

The whole endeavor began with what will be able to properly condition my 2nd floor (uneven cooling now due to orientation of the house along the lines of +7 degF back vs front). There will be zoning to address this unevenness from solar radiation.

HVACNUT

JustinS said:

I'm not familiar with the thermostats you listed, but staging is done though it. As long as everything is wired correctly.
Have you looked into 2 stage heat pumps? You could potentially have 2 cooling stages and 3 heat, with stage 3 being the boiler. That's pretty much my plan when it's time to replace my AC. I'm swinging between 2 stage and inverter. I'm leaning towards the KISS method.

I hadn't really considered 2 stage heat pumps, both installers started with variable capacity ones. The whole endeavor began with what will be able to properly condition my 2nd floor (uneven cooling now due to orientation of the house along the lines of +7 degF back vs front). There will be zoning to address this unevenness from solar radiation.

So you're going mini splits, or 2 CAC systems?

pecmsg

JustinS said:

HVACNUT said:

I'm not familiar with the thermostats you listed, but staging is done though it. As long as everything is wired correctly.
Have you looked into 2 stage heat pumps? You could potentially have 2 cooling stages and 3 heat, with stage 3 being the boiler. That's pretty much my plan when it's time to replace my AC. I'm swinging between 2 stage and inverter. I'm leaning towards the KISS method.

I hadn't really considered 2 stage heat pumps, both installers started with variable capacity ones.

The whole endeavor began with what will be able to properly condition my 2nd floor (uneven cooling now due to orientation of the house along the lines of +7 degF back vs front). There will be zoning to address this unevenness from solar radiation.

Zoning as in Duct dampers or as in separate systems?

JustinS

HVACNUT said:

So you're going mini splits, or 2 CAC systems?

2 CAC systems, there will be 3 zones in total... 1 downstairs on one unit, 2 upstairs on another unit

pecmsg said:

Zoning as in Duct dampers or as in separate systems?

Duct dampers on the 2nd floor, none on the 1st as it's pretty open floor plan