Worth upgrading 13 year old boiler to mod/con with heat pump?
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The problem as I see it is that your electricity is quite expensive and even with a COP of 2 at 5 deg F, it’s more than running your gas boiler. I assume you are using a modern thermostat that automatically will select when you run the boiler instead of the heat pump. You can rough in your COP’s by making a graph with the points you know and interpolate between them then find out when your heat pump cost is exactly the same as the boiler cost. Then pick a temp slightly above that to use as your set point for when to operate the boiler. Your heat pump can run more efficiently than your boiler but your power costs too much to bother doing that.
I’m going to guess your heat pump has a COP of 3 at about the freezing point. At that set point it would run at almost the same price as your boiler so, you could probably switch to the boiler when it’s freezing outside. If your power was cheaper you could have run it economically at a much lower temperature, Does that make sense?
I have a 3 ton heat pump that is 12 years old and can only run as low as 27 F before it goes into the thaw mode when the humidity is high. My back up is a propane fired boiler. I have cheap electrical power, at $0.10 US per kWhr and expensive propane at about $3.20 US per gallon. At 27 F the heat pump switches to the boiler which uses a heat exchanger in the air flow of the furnace. So, two heat exchangers, one for the heat pump and one for the boiler. That same boiler provides heat to the water tank.
I’m going to guess your heat pump has a COP of 3 at about the freezing point. At that set point it would run at almost the same price as your boiler so, you could probably switch to the boiler when it’s freezing outside. If your power was cheaper you could have run it economically at a much lower temperature, Does that make sense?
I have a 3 ton heat pump that is 12 years old and can only run as low as 27 F before it goes into the thaw mode when the humidity is high. My back up is a propane fired boiler. I have cheap electrical power, at $0.10 US per kWhr and expensive propane at about $3.20 US per gallon. At 27 F the heat pump switches to the boiler which uses a heat exchanger in the air flow of the furnace. So, two heat exchangers, one for the heat pump and one for the boiler. That same boiler provides heat to the water tank.
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I have one them. It’s a Viesmann propane fired condensing boiler and has a high speed computer controlled fan injecting the propane, a fancy gas valve with a plastic venturi and an auto igniter. The front cover of the combustion chamber should be removed each year for cleaning and the igniter should be replaced. My old boiler in another house was so much simpler.
May I suggest you keep the existing boiler and replace the water heater with a new one. The service life of that boiler is probably 25 years.
If working well, I would keep what you have. When you replace the water heater, get an indirect and add on to the boiler or get a tankless wall hanging one depending costs at that time. Keep future plans in mind (bathroom upgrades/soaking tube etc.) My mom has a walk in therapy type tub with all the whirlpool and micro air jets. She mostly will sit and just use the handheld shower normally. We had gotten it for my dad but he passed before really using it. She just got a new 40 or 50 gallon water heater (electric) and it will NOT fill the tub with hot water. I tried it to clean the jets etc with some bleach as recommended.
I have an older Peerless oil version with hot water baseboard. It had a tankless coil when I moved in. I put a Superstor Indirect on it in place of coil and made it cold start. I don't run out of hot water now, and my oil use dropped about 350 gallons. I have the TACO controller and 4 circulators. The indirect is on a priority zone. I also added a Field Oil Vent Damper, it basically shuts off the flue when not in use so heat stays in the boiler not running out the chimney all day everyday. That helped savings.
I have a Bosch Heat Pump but it is only one zone for my Colonial. I use that for AC for summer (and early in spring through late fall). I set it to heat for the shoulder seasons and winter. Once it gets down colder my boiler T-stat for second floor is right next to heat pump T-stat. I have them set about 1 degree apart. The baseboard will turn on and heat up accordingly, the heat pump helps circulate everything keeping it more comfortable and even quicker. Since setting it that way my oil use is down my electric usage is down a lot since old AC only was very inefficient.
Some of the newer circulators also have freeze out sensors like described. They will turn on for a very short time to keep everything moving.
Many of the new aquastats have a built in economizer like an outdoor reset. I have a Beckett with Heat Manager in it. Old house I installed an Intellicon. It senses how fast the water temperature is dropping. If dropping slow it won't fire the head. It will circulate the 140 degree water for a longer time so you gradually heat up with no fuel just residual heat from boiler. If dropping quick it fires right away up to what ever set point. I think mine also shuts earlier depending on conditions it sees. Indirect water heater zone demand fires instantly to get water hot ASAP. Boiler is setup as cold start so if no heat needed or hot water it goes to room temperature. It never does with 5-6 adults in the house doing showers at different times.
My old house I replaced a Repco oil fired boiler with tankless coil. I installed a Weil McClain oil fired with a SuperStor Indirect. I added the Intellicon and the Flue Vent Damper. Replaced some windows and added extra Attic insulation as well as walls in "nursery" when I redid the room. My oil usage went down about 600 gallons per year. Less than 1/2 what I was using originally. New owner wanted to replace the system with an updated Gas version since they ran gas down the street after I installed it. Plumber told him just get the Carlin gas head and nothing else. Said you will never recover the costs from how efficient it was and how it was setup.
I have an older Peerless oil version with hot water baseboard. It had a tankless coil when I moved in. I put a Superstor Indirect on it in place of coil and made it cold start. I don't run out of hot water now, and my oil use dropped about 350 gallons. I have the TACO controller and 4 circulators. The indirect is on a priority zone. I also added a Field Oil Vent Damper, it basically shuts off the flue when not in use so heat stays in the boiler not running out the chimney all day everyday. That helped savings.
I have a Bosch Heat Pump but it is only one zone for my Colonial. I use that for AC for summer (and early in spring through late fall). I set it to heat for the shoulder seasons and winter. Once it gets down colder my boiler T-stat for second floor is right next to heat pump T-stat. I have them set about 1 degree apart. The baseboard will turn on and heat up accordingly, the heat pump helps circulate everything keeping it more comfortable and even quicker. Since setting it that way my oil use is down my electric usage is down a lot since old AC only was very inefficient.
Some of the newer circulators also have freeze out sensors like described. They will turn on for a very short time to keep everything moving.
Many of the new aquastats have a built in economizer like an outdoor reset. I have a Beckett with Heat Manager in it. Old house I installed an Intellicon. It senses how fast the water temperature is dropping. If dropping slow it won't fire the head. It will circulate the 140 degree water for a longer time so you gradually heat up with no fuel just residual heat from boiler. If dropping quick it fires right away up to what ever set point. I think mine also shuts earlier depending on conditions it sees. Indirect water heater zone demand fires instantly to get water hot ASAP. Boiler is setup as cold start so if no heat needed or hot water it goes to room temperature. It never does with 5-6 adults in the house doing showers at different times.
My old house I replaced a Repco oil fired boiler with tankless coil. I installed a Weil McClain oil fired with a SuperStor Indirect. I added the Intellicon and the Flue Vent Damper. Replaced some windows and added extra Attic insulation as well as walls in "nursery" when I redid the room. My oil usage went down about 600 gallons per year. Less than 1/2 what I was using originally. New owner wanted to replace the system with an updated Gas version since they ran gas down the street after I installed it. Plumber told him just get the Carlin gas head and nothing else. Said you will never recover the costs from how efficient it was and how it was setup.
Remember, the power plant that produces your electrical power consumes something. If it burns 1 gallon of oil, or 10 pounds of coal, or 132 cubic feet of natural gas, what you get at your home is 14.25KWh, national grid average.
So, if it matters to you, you can see that running a heat pump with a COP under 2, will consume more energy than simply burning the fuel in a relatively efficient manner. A COP of 3 is roughly equal, energy in to heat out.
In other words, what's it matter if the heat pump is efficient, if the grid is not?
Cost is another matter entirely. And, as always, don't forget to look at your total electric bill for the real cost, not just the KWh rate.
Energy audit says it’s as good as I can get it short of replacing a couple of windows. I’ve been slowly picking away at windows the past couple of years. I have a big picture window I plan on replacing In the spring.
I am in a suburb of providence. We usually have a week or 2 out of the year it will dip to single digits or around zero. But not consistent. I would say based on those numbers they are on the high side of averages based on what I observe where I live.
currently controlling the heat pump with the Mitsubishi remotes. I have 4 heads controlled by a branch box. I use nests for the boiler. I plan on watching my power consumption and thought about getting a “sense” module to monitor heat pump power consumption. If I can keep it at 30kWh per day for heating only it will be cheaper than my boiler. It will be tough to distinguish without monitor as I have electric oven and stove top, and electric dryer. And yes, what you say makes sense. I was leaning toward keeping the one I have but have found the fuel savings will not be worth it. If the boiler had issues it’d be a much easier decision. But it really doesn’t.
it’s not worth it to me to modify the current boiler supply/return piping and get the indirect heater. Not worth the cost or time to me. But if I as already there changing the entire set up with a condensing boiler i would do it. I’ll just change the water heater (going to an AO smith 40 gal/40k btu). Heating my hot water only not including connection fees only costs me about $22/month. It would cost me probably close to 2500$ for an good indirect tank, circulator, controller and piping. The AO smith costs 1025$. I’ll probably need a couple hundred bucks worth of copper pipe/fittings to do that.
This will be a good experiment. I take it you’ll try to run the heat pump to at least freezing conditions (32 F). Since the cold weather will be be from Dec 1, to the end of Feb, I’d recommend running the heat pump and occasionally taking output temps at a hot air register ( the same one each time). I use a laser guided infrared heat gun you can get from your local big box store or Amazon.
As you go lower the outside humidity might start to cause freezing issues on the outdoor coils and the system might go into the defrost mode. If that happens I would switch to the boiler mode. If it doesn’t, keep going and record your temps at the register. You might spend an extra amount on power but at least you’ll find out what the heat pump is capable of. Many of us will be very interested to see how it does. Finally when the heat pump is near it’s max it will on almost 100% of the time. She’ll be giving all she’s got Captain.
As you go lower the outside humidity might start to cause freezing issues on the outdoor coils and the system might go into the defrost mode. If that happens I would switch to the boiler mode. If it doesn’t, keep going and record your temps at the register. You might spend an extra amount on power but at least you’ll find out what the heat pump is capable of. Many of us will be very interested to see how it does. Finally when the heat pump is near it’s max it will on almost 100% of the time. She’ll be giving all she’s got Captain.
It's most likely to happen above 32F outdoor. The further below 32F it gets, the less humidity there is in the outdoor air and the less likely it will need a defrost.
The worst is when it's between 32F and 40F and raining outside. Then it's one defrost cycle after another.
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I didn’t realize it’s a mini-split. Instead of a register, use your temp gun to monitor the output temp of one of the heads, and then consistently monitor the same head across the winter. I’m going to guess it will be around 100 F but I will be interested to see if it changes as the outdoor temp goes lower. Keep us posted!
Your electric cost is sky-high and will go higher over the years, if it was me I wouldnt give up my gas boiler for any reason and the unit at its current age is young. Even if you're dying to get rid of it, better stuff will come along in the next ten years which will make you wish you waited or at least that is how I would feel.
Keep in mind I have solar will off set some cost in winter, but not a lot. I haven’t had electric bill from March and my first will I will have to pay is December.
I wasn’t giving up a boiler all together, just debating whether to upgrade to a condensing unit or not. But the fuel savings does not seem worth the investment.
Yeah, I got most of your meaning while I have my first coffee of the day.
Sometimes I type too much and the meaning gets lost. If I am understanding correctly you would get rid of the natural gas. Me personally I wouldnt. I dont like the idea of being held to one utility without choices. Yes I picked up on the solar but also your statement its output isnt much in the winter. I did miss you would keep the boiler.
I do think for you it's a gray area.
For me, if I had the choice I would always choose to stay in N.G. Last home of 15 years had second floor heat pump, first floor NG.
Electric was inexpensive there too.
Our new home in our area the electric is dirt cheap 24 hours a day at 10 Cents kWr. Plus typical service charges that bring it up to 13 cents when averaged in. We do have a heat pump and we are in the Carolinas so that is fine/thoughless. Have a L.P. fireplace, hot water and stovetop. Oven is electric. I almost wish I didnt have LP but had no choice for the builder. The entire community that has been and still being built is LP I don get it, but whatever, people seem to love it. Call me crazy but I think the electric might be more cost effective? I guess some consider cooking with gas an "upgrade" and that silly instantaneous hot water heater. I prefer a tank but it is what it is.
Not really complaining, love the house.
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Yeah, I got most of your meaning while I have my first coffee of the day.
Sometimes I type too much and the meaning gets lost. If I am understanding correctly you would get rid of the natural gas. Me personally I wouldnt. I dont like the idea of being held to one utility without choices. Yes I picked up on the solar but also your statement its output isnt much in the winter. I did miss you would keep the boiler.
I do think for you it's a gray area.
For me, if I had the choice I would always choose to stay in N.G. Last home of 15 years had second floor heat pump, first floor NG.
Electric was inexpensive there too.
Our new home in our area the electric is dirt cheap 24 hours a day at 10 Cents kWr. Plus typical service charges that bring it up to 13 cents when averaged in. We do have a heat pump and we are in the Carolinas so that is fine/thoughless. Have a L.P. fireplace, hot water and stovetop. Oven is electric. I almost wish I didnt have LP but had no choice for the builder. The entire community that has been and still being built is LP I don get it, but whatever, people seem to love it. Call me crazy but I think the electric might be more cost effective? I guess some consider cooking with gas an "upgrade" and that silly instantaneous hot water heater. I prefer a tank but it is what it is.
Not really complaining, love the house.
If cost of electric was cheaper I would strongly consider it especially if it can do what it takes this winter. Full capacity at near 0*F is pretty good. I really only opted for this mini splits for cooling. Never really considered it for heating until I saw how fast it can bring the house temp up at 40 degrees. It brought the house up 10 degrees in less than 45 min and only consumed 2 kWH
Unless that changes I’ll be hanging on to gas fired equipment
Yeah, it's amazing how technology has leapfrogged. Gosh I remember decades back a builder building high end homes on Long Island with heat pumps. It was really sketchy at the time with concerns of temps around 30 degrees coupled with high Electric costs.
It's pretty cool having a project like you do, options good and you really have a handle on things. We all know electric will not get cheaper, though who knows what will happen with NG.
Im sure you are thrilled with the panels.
On the cost issues, when comparing one State to another State you need to add all those “add ins” and divide by the total amount to get a cost per kWhr, but when comparing your own electric cost vs natural gas cost, one doesn’t have to add in the “fixed” costs, just costs that change with the amount consumed. The premise is that you aren’t going to get rid of the service, so those fixed costs are always there, but they don’t count when deciding to run the heat pump vs the boiler.
Just so I understand, is that water tank heated by the boiler?
No. Stand alone atmospheric vent. Not worth it tapping into this boiler for indirect. It costs so little to heat hot water this way hard to justify the cost of indirect and time to plumb it. The setup would be twice the price of the one I just bought. If I was going to replace the boiler it would be different because I’d be changing the piping any way and purchasing necessary controller (no provision for independent DHW control with this aquastat). I’ll also have hot water in the event of a power outage this way.
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