Strategy for replacing oil boiler with electric boiler/heat pump

mmnyhv

Our 1800-sf ranch house in NYS has a hodgepodge of heating and cooling systems.

An oil boiler (20 yo, with significant overhaul when we bought the house 3 yrs ago) heats our house via hydronic baseboards. It also heats the water, which is stored/managed by an indirect tank (added 2 years ago). Also replaced the oil tank (2 years ago).

We added (3 years ago) central AC throughout the house via new ducts through the attic. Compressor outside, air handler in the attic. Ceiling vents in each room.

We pulled the baseboard heaters (3 years ago) from the 3 bathrooms and put in electric radiant in the floors.

We finished the basement (2 years ago), and put in electric baseboard heaters throughout to warm that.

That’s all the preamble… The question is, what would be the best move for getting rid of the oil boiler entirely?

Why?

One, we want to transition away from fossil fuels generally.

Two, we have an insanely steep driveway and have genuinely had some close calls in terms of getting oil deliveries during the winter (I had a weeklong stretch one winter where the oil truck could not make it up our driveway and I was driving to the gas station and filling up a 5-gallon diesel can to make sure we didn’t run out of fuel).

Three, the boiler blower is loud and smelly, and switching to a chimney to alleviate those problems will cost around $9k.

Four, maintenance on a 20-yo boiler is real and regular.

So…

Do we keep the hydronic heating setup upstairs and replace the oil boiler with an electric boiler?

Do we let the hydronics go completely unused and instead replace the AC with a heat pump capable of heating as well as cooling, sending heat to rooms via the ceiling AC vents? (We’ve lived in a house with ceiling-vent furnace heat before, so I’m aware that there are drawbacks in terms of heat delivery).

Something else???

In any case, do we add an electric water heater for our water heating needs? Tank or tankless? Or if we use the electric boiler, should we hang on to the indirect tank?

And yes, we do lose power in the winter on occasion. But when we do, we also lose the ability to run the oil boiler, so switching to all electric is no greater risk in that regard.

Thanks for the input.

Jamie Hall

Well... we go around on this from time to time.

If you don't want to go broke and you want to at least come close to reducing your fossil fuel use, you must switch to a heat pump.

Let's take the go broke first. Last I looked, New York had some impressively high electricity prices, and they aren't going to go down. You can figure it out yourself. You will need the same total amount of energy to heat the house, whether you go electric or oil. An electric boiler is straight resistance, which means that the equivalence is 1 KW is equal to about 3400 BTU per hour. Take your oil delivery from last year, multiply that by 140,000, and that will give you the total BTUs you needed last year. Now divide that by 3400 and that will give you the total kilowatt hours of electricity you will use. Multiply that by your electrical rate from the power company and there is your cost. Harder to describe than to do.

Now fossil fuel use... a good portion -- like most of it -- of your electricity is generated by fossil fuels. The overall fuel to house efficiency of the grid is around 33%/ So if you go straight electric resistance heating, you will be using around 3 times the fossil fuel that you are using with your current oil burner.

Now. If you can find a heat pump with a COP of at least 3 at your design temperature, that would use the same amount of fossil fuel as your boiler at that temperature. Since the COP of heat pumps increases with increasing outside temperature, overall you will be using less fossil fuel.

You will also get the running cost for the electricity down to something competitive with the oil burner.

Maintenance on the heat pump will be about the same as the oil burner, if you do it right. The heat pump won't last as long.

You mention the difficulty of supplying oil on a steep driveway. This is a problem., however with decent planning this can be avoided. How often do you get fuel? With that size house I'm guessing every three weeks or so? Some planning ahead with your oil company and you should be able to have a full tank or close to it before any storms...

You also mention that the power goes out from time to time. You can run an oil burner from a 1500 to 3000 watt portable generator. No problem at all. You should have one anyway, if only for the refrigerator. You cannot run ether a heat pump or, worse, straight resistance, from such a generator -- you'd need a much bigger one.

Hot_water_fan

First step is determining the heat load, which should be easy since you'll be able to get oil receipts. Remember to subtract out a reasonable amount of oil for the indirect DHW.

https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new

Unfortunately, you have a 3 year old AC unit, not a 3 year old heat pump. Often, manufacturers make both an AC only and Heat pump version of the same units. If possible, start there for a replacement and you can reuse the air handler. If it's not a variable speed outdoor unit, that might be a worthwhile upgrade. I would usually say that the unit that's right-sized for cooling won't be big enough for heating in your climate, so you'll need some sort of back-up heat. However, you already have some electric back-up in the house, so additional heating may not be necessary. We'll see after the heat loss.

In this order, I'd try A. integrated electric backup in the air handler, B. more electric baseboards/radiant floors like you already have, C. the electric boiler. The electric boiler is just a lot of complexity for no real benefit. The only benefit of electric boiler is that you have a new indirect tank, but buying an electric tank and eating that loss will probably be cheaper than installing an electric boiler.

You may consider a heat pump water heater, more expensive but about 4x more efficient.

Skip the tankless electric water heater - they require a ton of amperage (possibly requiring a panel upgrade) with no benefit besides marginal space saving.

You can abandon the water baseboards, either removing them entirely, or keep them in place and wait on more air-to-water heat pumps to reach the market (if you think it's worth it comfort wise).

EBEBRATT-Ed

@mmnyhv

I think your going in the wrong direction. Electric power is generated by fossil fuels and as @Jamie Hall pointed out you will use more fossil fuel than if you stayed on oil.

I would fix up the old boiler or put a new one in.

A heat pump in Newyork is a bad choice in the dead of winter.

It's ok in the fall and spring

Unless you go all solar your staying on fossil fuels one way or the other

Hot_water_fan

The EIA has New York's CO2 lbs/kwh at .415 in 2019.
That's about 40-50 CO2 lbs/ 1,000,000 BTUs using a heat pump. Oil is about 191 CO2 lbs/1,000,000 btus.
You'd be saving about 75-80% of the emissions. Solar would push that number higher and save you more money.

mmnyhv

Not to quibble, but our local energy co-op only buys renewable energy generated from within NYS, so the added fossil fuel impact of going all-electric is minimized.

pecmsg

Good luck but the resources aren’t available now or in the near future. 

The best you can hope for is offset with a heat pump for 50 - 65% of the season. You’ll still need oil!

Jamie Hall

mmnyhv said:

Not to quibble, but our local energy co-op only buys renewable energy generated from within NYS, so the added fossil fuel impact of going all-electric is minimized.

Right. All that means is that some other **** is forced to by all fossil fueled electricity. Electrons don't come colour coded, and if you local grid is connected to the rest of the state... that's one of those statements which sounds wonderful and are, bluntly, nonsense.

Hot_water_fan

@pecmsg That doesn't make any sense. You can offset 100% with a heat pump + electric backup. Oil is entirely optional here.

pecmsg

You can but can you afford it. Double and or Triple your current monthly elec bills. Hope you have at least 200 Amp service. Possibly 300 needed!

Hot_water_fan

I don't know @mmnyhv's rates for electricity/oil (they'll change anyway) but the fuel cost of heat pumps, especially with solar, are often very favorable vs. oil. Of course, the heat loss of the house is very important in all of this for backup requirements. Pretty easy electrification here, all in all.

mmnyhv

Heat pumps are hardly unknown up here—nearly every new build and every retrofit I come across is a heat pump (either central or mini-split). Things are vastly different than they were 10 years ago.

mmnyhv

Hot_water_fan said:

I don't know @mmnyhv's rates for electricity/oil (they'll change anyway) but the fuel cost of heat pumps, especially with solar, are often very favorable vs. oil. Of course, the heat loss of the house is very important in all of this for backup requirements. Pretty easy electrification here, all in all.

That's spot-on with our electric rate ($0.18/kwh); our oil here has averaged about $2.80 over the last 3 deliveries.

And thanks for that Green Building Advisor article—I'll take a crack at the calculations when I have some free time.

mmnyhv

OK. So, going through the calculations outlined at the GBA article, I come up with an implied load of 39158 BTU/Hr at a 60°F balance point (I have 2x6 walls, which are indicated to be more likely 60° than 65°).

The question, per your earlier post, is how much of that falls to domestic hot water, rather than heating?

Canucker

mmnyhv said:

OK. So, going through the calculations outlined at the GBA article, I come up with an implied load of 39158 BTU/Hr at a 60°F balance point (I have 2x6 walls, which are indicated to be more likely 60° than 65°). The question, per your earlier post, is how much of that falls to domestic hot water, rather than heating?

I don't know what the calculations were but if it's a heat loss your number has absolutely no dhw included. If it's a fuel use calculation, it depends

mmnyhv

Well, you can refer to the link ( https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new ) for clarification:

You can calculate a building’s heat load in 15 minutes

You have instrumentation already in the house that is measuring the heat load: namely, the existing heating equipment. The way to use it for measurement purposes is:

• Take a mid- to late-winter fuel bill, and note the exact dates covered by the bill — the fill-up dates or the meter-reading dates.
• Look for a specification label on your furnace or boiler that includes the input BTU/h rating and the output BTU/h rating for your equipment.
• Download base 65°F or base 60°F heating degree-day spreadsheets covering those dates for a nearby weather station from a website called DegreeDays.net.
• Look up the 99% outside design temperature (sometimes called the “heating 99% dry bulb temperature”) for your location from a website — for example, from an online document called Manual J Outdoor Design Conditions for Residential Load Calculation.

It then runs through the calculations. Here are my inputs:

99% temp for area = 2° F
Heating Degree Days during billing period (2020-11-05 to 2021-01-10) = 1582
Gallons of oil used during period = 211.6
Boiler efficiency = 87%

And my calculations (note that some decimals have been rounded by the spreadsheet):

BTUs used during period = 138700 BTUs/Gal of oil * 211.6 Gals of oil = 29348920 BTUs

Net BTUs delivered by system = 29348920 BTUs * 0.87 efficiency = 25625550 BTUs

BTUs per Degree Day = 25625550 BTUs / 1582 DD = 16203 BTUs/DD

BTUs per Degree Hour = (16203 BTUs/DD) / (24 Hours / Day) = 675 BTUs/DH

Implied load = (60° [balance point] - 2° [99% temp]) * 675 BTUs/DH = 39158 BTUs/H

Jamie Hall

That's actually not too bad, and your existing entrance panel may be able to handle it. 50 amps at 240 volts resistance heating. Now please note: a heat pump, operating in heat pump mode, will probably only use about 20 amps of that. However, if the heat pump can't handle the load on a cold day, it will switch to resistance heating -- and draw that 50 amps. It will also draw close to that if it has to defrost (it will). So you'd need probably a new 60 amp 249 volt (that's double pole) circuit.

Your electrician will be able to tell you whether you have the space and capacity in your service entrance and switchboard to handle that.

Needless (I hope) to say, you'll not run that off a normal size household generator when the power goes out. Also, you'll not run that off of solar PV panels, if you were thinking along those lines.

Robert_25

Hot_water_fan said:

I don't know @mmnyhv's rates for electricity/oil (they'll change anyway) but the fuel cost of heat pumps, especially with solar, are often very favorable vs. oil. Of course, the heat loss of the house is very important in all of this for backup requirements. Pretty easy electrification here, all in all.

How are you calculating the cost of on-site solar? I see that you have allowed $0.06 per kwh for it, but not sure how you arrived at that figure.

mmnyhv

Jamie Hall said:

Well... we go around on this from time to time.

If you don't want to go broke and you want to at least come close to reducing your fossil fuel use, you must switch to a heat pump.

...

You will also get the running cost for the electricity down to something competitive with the oil burner.

If the spreadsheet from this thread is accurate (I plugged in the actual oil and electric prices for my area, along with the HSPF of a likely heat pump and the modifiers for my actual location...), then heat pump is definitely the only thing that, long-term, will be similar in running cost cost to (currently priced) oil.

Geothermal would be something, but I don't know if I want to go to that level of expense and disruption.

Hot_water_fan

@mmnyhv



Without a summer fill-up, we can estimate it based on daily usage. It drops your total heat loss 5-18% based on these usage levels. Mid to low 30k Btus is a great spot for a heat pump, plenty are in that range.

Hot_water_fan

@Robert_25



It's variable for every situation based on financing, solar output, initial cost, etc. Here's one set of levelized cost of energy inputs that gets you $.12/kWh.

mmnyhv

Hot_water_fan said:

@mmnyhv
Without a summer fill-up, we can estimate it based on daily usage.

Here's a log of my fill-ups since last winter (I don't have readily available data earlier than that):

mmnyhv

Also, re: DHW: since I already have the indirect tank, can I use that in conjunction with an electric tank water heater to increase my DHW supply? Or should I just ditch the indirect?

Hot_water_fan

If the spreadsheet from this thread is accurate (I plugged in the actual oil and electric prices for my area, along with the HSPF of a likely heat pump and the modifiers for my actual location...), then heat pump is definitely the only thing that, long-term, will be similar in running cost cost to (currently priced) oil.

That COP of 179% for the air-source heat pump is way low for today's technology (would include a lot of resistance heat)- The cold climate Mitsubishi can hit that at 0 degrees and max output and would be >3 for all temps above 20. Modulating compressors greatly improved efficiency and often approach geothermal numbers.

Hot_water_fan

Also, re: DHW: since I already have the indirect tank, can I use that in conjunction with an electric tank water heater to increase my DHW supply? Or should I just ditch the indirect?

You could, with some work. Do you have any huge hot water users? Like a jacuzzi tub or something?
Hindsight is 20/20, it's hard to ditch it when the indirect is so young. Maybe someone on here will buy it off you.