Conventional heat pump t-stats have "emergency heat" setting right there with heat/cool/fan settings. If that's not what you have, install one. At most the only alternation you might have to make is an extra relay between t-stat and boiler relay.

Where are you located?

What are your energy rates?

Size of your house?

Is NG available?

More details about your systems?

Are any of your HP air-to-water?

SR

Where are you located? CT

What are your energy rates? Current: Oil 352.9/gallon 2025-26 season, Elec. 11.19/ kwh

First year 2021 used 1300 gal oil with 3 window AC units

2022 1-HP system and 900 gal oil, heat and AC

2023 2 HPs and 600 gal. oil, heat and AC

2024 2 HPs and 500 gal oil, heat and AC

Size of your house? 3000

Is NG available? No

More details about your systems?

Oil fired boiler with 5 zones, Boilermate

System 1 Mitsubishi 36000 BTU unit with two-12k minis and two-9k minis.

System 2 Mitsubishi 48k BTU unit with 30k Air handler/ducted, 12k mini, 6k mini

Are any of your HP air-to-water? No

I have the dollar amounts of the oil use and electric bills broken down by 12 month periods, though I don’t have the actual kwh usage, would have to do some digging to get info for prior years.

I was certain Joanne already did her research and decided she wanted to use the boiler more and was asking how to make that possible on system with single t-stat since it defaults to HP.

Following is the information which lead me to that conclusion.

"The other side has one thermostat for both heating methods with the HP as the default."

and

"Is there a way to separate the two heating sources so that we can opt to use the boiler instead of the HP?"

I re-read original post TWICE and I still believe I clearly understood what she asked for. I did not see anywhere that she asked if it would be a good idea to use boiler instead of heat pump or if it would be cost effective. Which brings us to why I'm asking those reading this for their help.

I thought fsq4cw simply misunderstood the question so I didn't give it second thought

until Joanne responded in a way that indicated it was ME that didn't understand her question. I was stunned! Why? Because I am older than both recent USA presidents at their inauguration. Much has been discussed recently about mental acuity of men that old and what they can offer society.

This is no small matter and thankfully I have grandkids that are qualified as well as dedicated to supporting me. One is a pharmacist ,one is a paramedic , one is a school teacher and another is an RN. I am blessed these and others frequently pop in for coffee,conversation and offers of assistance, be-it move furniture, plan a concert or discuss health issues. I printed original post and all responses on separate sheets. Do the good folks here think I'm understanding question in original post and should throw sheets in trash or should I ask kids to appraise them for indication therapy might be needed? Thank you so very much for your indulgence .

Klem1, no worries. I am not far behind you in years, and have looked everywhere for my phone while it was in my hand, and once put it in a kitchen cabinet to free up my hands, and closed it walked away. That took a while to find, especially since it was on silent.

You probably just skimmed my original post and didn’t quite take in all of it on the first go-round. Notes and printouts are your friend (and mine!)

Re: Joanne

I’m still somewhat unclear as to how many heat pumps and air handlers you have and of what types.

Usually electrical utility costs are fixed for grid hookup so that might not be of any real consequence unless there are other factors involved. Your electrical rate of 11.19¢/kWh seems very reasonable especially given the efficiency of most well-performing heat pumps.

My preferred installation would be 1-integrated ‘central’ hydronic heat pump (air-to-water or ground-to-water) for everything, heating, air-conditioning, domestic hot water (DHW) where you have true integration and all water distribution. That is likely not practical at this time for your home.

What I would suggest for you would be to find a well experienced hydronic specialist to not only look-at but also test and measure your entire hydronic system. That is its source, the boiler and its distribution system - 2-separate, connected and interdependent systems evaluated completely. That is to first determine whether every component on either side (source or distribution) was properly selected as designed, properly installed in the ‘right’ position and order to provide maximum efficiency as designed and to see if it still is functioning efficiently. They would have to study the layout and accurately measure performance of each zone and zone component and most importantly know how to do this. To check the state of pumps & rotors, zone valves, emitters (radiators) and water chemistry among many other things. Water chemistry and air (oxygen, iron oxide, rust, sludge) which affect pipes, especially iron, pump rotors, especially metal, emitters - almost everything!

All this is especially important if renovations through the years included extending or modifying the original design. All emitters (panel radiators, fin tube radiators, even (high wall) air handlers have to be inspected for dust, dirt, pet hair blockage and inefficiencies. In other words, you need the right person to advise you on what you have, how it’s performing and how it might be made better (greater efficiency).

You need someone you can talk to, communicate with that will explain things on your level - that knows what they’re doing. They will be able to advise how to best use your different systems together and get the greatest efficiency and value out of what you now have.

You might also discuss an annual service contract with them as maintenance is vital to performance and efficiency.

IMPO

SR