Adding a heat pump to a steam setup

1peterpan1

Hello everyone,

I'm exploring the possibility of integrating a heat pump into my home's heating system and would appreciate any advice or experiences you might share. Here are the key details:

• Home Details: Our home is a 2,000 sqft, two-story single-family house built around 1943, located in New England.
  
• Current Heating System: We currently use a one-pipe steam heating system powered by a natural gas furnace that's about 15 years old. While we're generally satisfied with the heating performance, the annual cost for natural gas is approximately $3,000, which is quite high.
  
• Existing HVAC System: A few years ago, I installed a ducted HVAC system for cooling, with the main unit in the attic and ducts extending to the ceilings of both floors.
  
• Interest in Heat Pumps: With the availability of massive rebates, I'm considering the feasibility of installing a heat pump to utilize the existing AC ductwork during winter. The goal would be to primarily rely on the heat pump, reserving the steam system for backup during particularly cold spells.
  

Concerns & Considerations:

• Efficiency of Ceiling Outlets for Heating: I'm aware that having outlets in the ceiling might not be ideal for heat distribution, given that heat rises.
  Climate: Our region experiences significant cold in the winter, which raises questions about the heat pump's effectiveness and the need for supplemental heating.
  

Questions for the Community:

1. Has anyone successfully integrated a heat pump with existing AC ductwork in a similar climate? What was your experience like?
   
2. Are there specific models or systems you would recommend that are effective in colder climates?
   
3. Any suggestions on how to address potential issues with ceiling ducts for heating purposes?
   
4. For those who've navigated the rebate process for such an upgrade, any tips or advice?
   

GW

Hello New Englander

are you discussing whole home rebate $10.000 or partial home rebate 1250/ton? The word “integrated” is specific language in the masssave program. Too confusing not knowing what topic we are on

technically, the steam system will need to be disabled, or removed.(whole home rebate). MassSave contractors have to follow the rules (rules changes several times in 2023). The electrification movement is still at its infancy. 

Duct layout, you need to get some HVAC people there to give you some opinion and commentary. The layout of the duct system is key, to how comfortable you’ll be when it’s single digits outside. Bathrooms— you’ll need some electric 

Clearly, you have an older home (steam), seems unlikely ducting sized for AC is going to heat your home well. (Whole home rebate). Currently, natural gas is the least costly means to heat a home. Electric rates in MA are very high. (Unless you’re current heating system is running poorly- your heating wills will certainly be higher)

We have worked with Bosch heat pumps and Bryant extreme heat pumps.

if we’re talking, partial home rebate, yes, good move.
whole home—- better have a really good hvac guy to properly set the table (expectations) 

Gary 

Hot_water_fan

This is a common situation. To compare fuel costs:

gas: $/therm x 10 / COP
heat pump: $/kwh x 293 /COP

If it makes sense, then look into a cold climate heat pump. I have a ducted Mitsubishi that does great in the single digits, and here, is substantially cheaper than gas. 

Jamie Hall

We have a Carrier four head mini-split for my wife's apartment (don't ask...) which supplements Cedric in her area -- she likes it a lot warmer. The Carrier works well down to about 0, but pretty well quits below that. It is NOT cheaper to run than Cedric, but is cheaper than electric space heaters. She likes it, and it is a very good arragement.

If you need to rip out the steam to get your hands in the taxpayers' pockets (which is what the rebate is), don't do it. You won't be happy with the results -- either in terms of usual day comfort or when it gets genuinely cold out.

If, on the other hand, you plan to use it on warmer days -- say 20 and up -- while you won't save money in Connecticut, nor saving on fossil fuel, you will have the satisfaction of having it.

Hot_water_fan

@Jamie Hall no politics please. 

ethicalpaul

It will work fine. And it is cheaper to operate than Cedric, within its operating range. At -20F Cedric wins for sure.

hot_rod

Start with the fuel cost calculation first. As you can see energy costs can vary quite a bit. Be sure to use delivered cost from the bottom line if your bill.

In areas of Maine  power costs go as low a 1 cent per kwh for off peak rates

a heatloss calc and energy audit with a blower door test might show ways to lower you energy use

Jamie Hall

Yes. As @hot_rod says, the energy cost calculation is critical in evaluating this sort of thing. Start there.

GW

Jamie the rebates in MA are Utility. To call it 'tax payer' is semi OK but not exactly correct.

bombaloo

What is your homes thermal envelope like. Did you do air sealing and insulation? R60 roof? Exterior insulation? Spray foaming rim joists? These types of improvements could lower your gas bill. 

Steamhead

@1peterpan1 , do NOT rip out the steam system. Get the heat pump if you want, but keep the steam. Don't abandon something that works well for something that doesn't.

Get a pro to look at your steam system to make it work as well as it can. If you're near Boston, call @New England SteamWorks . If you're on the other end of the state, call @Charlie from wmass . They're two of the best.

New England SteamWorks

And then there is this:

ethicalpaul

Yes ever since fracking, natural gas has been very cheap. Even in my CT house that I talk about all the time, I only just broke even against natural gas with my ground source heat pump, but that wasn't an option for me, I only had oil available, and the article conveys that vs oil it still a clear winner (as I found)

Charlie from wmass

Nj and MA are different climates. We are tundra compared to NJ.

ethicalpaul

Who said anything about NJ?

The article that I screenshotted above and was linked higher above was written in MA

Jamie Hall

Charlie from wmass said:

Nj and MA are different climates. We are tundra compared to NJ.

Not only that, but there's MA and MA. Boston metro is pretty balmy compared to the Berkshires...

Charlie from wmass

Your signature says nj and ct is also 2 growing zones warmer

ethicalpaul

I have lived in different places, it's true The article, though, as I said, is from MA.

I even lived in Michigan which will give MA a run for its money, but let's be honest, neither of those states can hold a candle to the plains.

winnie

I'm late to this thread, but have relevant information.

I live in a house built in 1935 with an oil fired one pipe steam system.

I installed Fujitsu minisplit heat pumps. I removed the old central air system, specifically the old and leaky attic ducting. I specifically kept the steam heat system.

My thought process is that heat pumps get less efficient as the temperature difference increases. COP is highest when you need minimal heat and lowest when you need the most heat.

On the other hand the steam heat is inefficient when you only need a little bit of heat; think about operation on a cool spring day; the thermostat calls for heat, the boiler fires up and spends 5 or 10 minutes building up steam, then the steam gets to the radiators, the room gets the bit of heat that it needs, and then the boiler turns off a couple of minutes later.

So my design intent was to use the minisplits for shoulder season heating, and to keep using the oil for heating on the coldest days. I pre-calculated that my cut-over point was to use the minisplits for heating above 32F, or if I only needed to heat 1 room, and use oil whenever the temperature was below 32F. I'll probably revise these numbers at some point.

Over the past couple of years I've found:

1. The minisplits always blow air, even when heat is not being called for. This means you have a fan blowing even on a cold day. I definitely prefer the way the radiators feel when I am near the heat source. Away from the minisplit heads I can't tell the difference.
2. The minisplits are capable of producing heat even on the coldest day. They are rated to heat down to -5F, but produced heat at -8F outside. But per design I don't use them in this fashion. Just an option if something goes wrong with the oil system.
3. My annual electricity consumption went up by about 1000 kWh. My annual oil consumption went from about 350 gallons to 150 gallons, down by about 200 gallons.

Note that 200 gallons of oil is about 7800 kWh of heat. This apparent out of this world COP (replace 7800 kWh of oil with 1000 kWh of electricity) is because my summer air conditioning is more efficient (less summer electricity use) and I'm cutting out the least efficient oil use. My guess is that to replace the last 150 gallons of oil would take 2500-3000 kWh.

Hope this info helps.

Jonathan

ethicalpaul

That was really well written and presented and even better, I agree with the whole thing. What are you doing for hot water? Please don't kill me by saying an indirect.

DCContrarian

I would use the process outlined in this article:

https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler

To use records of gas usage to determine your approximate heating load. From that you can determine how many CFM of ducted air you need, figure 100 CFM per 3000 BTU/hr of heating. Then measure the height and width of the main trunk of your ductwork and go to an internet duct sizing tool to see i there's any chance your ductwork will be able to support that level of airflow. This will tell you if your ductwork is capable of handling the heating load (or rather, not incapable). This will quickly tell you whether the idea is worth pursuing.

There's a good chance it won't be. Massachusetts is pretty strongly heating-dominant, and if it was sized strictly for cooling it will be too small for heating.

GW

Winnie,

1000 kw is about $350 or so?

200 gallons is about $600 or so?

looks like you're ahead of the game by a mere $250

Also, if you don't want to feel the air blowing, you can simply turn the units 'off'. I know Mits has a small wire/jumper you can snip, to stop the fan from blowing. But- this is the only way the system knows how to sample the temperature of the room.

ethicalpaul

yeah and it samples the temperature near the ceiling, a very unfortunate aspect of heating with a mini split