Transitioning home heating from carbon fuel burning to electricity

If the existing homes have forced air furnaces, that means they have all the ductwork in place to heat the house. Or, if a boiler system, have radiators already installed. The question is what heat source is best used to warm the air or the radiators.

If you're going away from typical oil/gas energy sources, that really just leaves electricity. That means you either use the electricity FOR heat (resistive), or use the electricity to TRANSFER the heat. The latter is the most energy-efficient method of heating (and cooling) with electricity.

The 'transfer' scenario could be an air to air heat pump or a geo-exchange system (often called - incorrectly - 'geothermal'). Essentially, a refrigeration cycle. Transferring the heat is more efficient than electric resistive heat because you're just moving the heat from one place to another - i.e., the heat stored in the earth is moved to the house in the winter, and put back in the summer when air conditioning is desired.

The heat from the refrigeration cycle is then transferred to your forced air or radiant system.

It takes much less electricity to move the heat that become the source of the heat. Geo-exchange requires wells or trenches to be dug in the ground to provide the heat transfer source, but air to air systems are pretty good too, and will work in temperatures below freezing. Obviously, the air to air systems don't require much work or cost to retrofit as there is much more effort associated with drilling wells, but they aren't as efficient. Either are viable options in many areas though, and obviously are significantly more sustainable!

Why are you doing this?
to save emissions of CO2?
Where does your electricity come from?

EVs are nice because even if the source of your electricity is natural gas, your car still emits less CO2 per mile than a similar gasoline vehicle. ICEs are like 25% efficient. Natural gas power plants are like 50% efficient. Power lines and batteries aren't perfect, but you still come out ahead when you use the large, stationary power plant.

Heating doesn't work like that. A home furnace is like 95% efficient. It's rather easy to make heat out of natural gas: just add oxygen. (The 5% wasted energy is heat going out the chimney). It's much harder to make electricity.
If the power plant burns natural gas to make heat, and that heat is used to make electricity, and then power lines transport the electricity to your house, and then you use the electricity to make heat, well that contributes over twice as much CO2 to the atmosphere than if you just piped the natural gas to your house and created heat on site.

It's true that with a heat pump, you can add 10 kWh of heat to a room with only 1 kWh of energy. but that only works well when the temperature of the heat source is close to the temperature of the heat destination. When the temperatures are very different, you might only add 2 kWh to a room with 1 kWh of energy. Once you're back to that point, you can go back and see if your local power plant is burning 2.5 kWh of methane to give you 1 kWh of electricity, which you turn around to add 2 kWh of heat to your room when you could have added 2.3 kWh of heat by just burning it on site.
One thing that's done to improve performance is to try to use a warmer source of heat, like the 35°F ground rather than the 10°F air.

If you have a huge solar array on your house generating a surplus of electricity, the best way to save CO2 with that electricity is to sell the electricity to the grid. "Creatively" using clean electricity for things where natural gas is a more natural energy source (hydrogen generation, heat, etc.) is just wasteful. You might not be burning fossil fuels, but your local power plant still is.

In short, think through what you're trying to achieve.
The world isn't as simple as "Electricity is better than combustion".

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anticitizen13.7 said:

(1) Is it feasible to switch most home heating to electric?

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sure. just replace all of your light bulbs with 100W incandescents.

A good high efficiency furnace will get into the 90-95% efficiency range. Most people don't have them. 67-70% is more typical, with a few in the 80% range (mid-efficiency).

What's not noted is that the geoexchange units also cool your home in the summer... again with good efficiency. Sure, an air conditioner is essentially a heat pump too, but the ground exchange system is more efficient than hot summer air.

Where I am, electricity from the grid is about 85% green. It's a no-brainer compared to gas and certainly to oil. Where electricity is coal-fired, it might not be as good an idea. But if you put PV panels on your home and connect them to the grid, you're offsetting the dirty power with clean and the net carbon reduction will be better.

At some point, dirty power will have to go. Burning oil or gas at home will have to be reduced too. If you retrofit to a system that is truly green on its own, the net benefit will increase as coal plants are replaced with cleaner plants... or even Elon's solar solution.

If you're wanting to switch your heating, especially to electricity, I suggest you focus first on insulating your house as much as possible in order to lower the energy needed. If you can lower your energy needs you can buy a less powerful system.

How much you'll need depends on where you live and what temperature you want your house to be, and for electricity things are non-linear, because heat pump efficiency decreases with temperature.

I like the concept of just using electricity, for the sake of simplicity and configurability, but being cold here makes that a challenge.

I'll chime in. With extensive experience with all heating mediums between houses I or my family live in and rental properties managed, electric heat is by far the most expensive energy source. Heat pumps essentially stop working once you get below freezing thus are not a good solution for the northeast (requiring the use of the very most expensive electric resistive heat). This is exactly why using heat in the Tesla sucks up your range. If you install a expensive solar/geothermal heat pump type system it will be more energy efficient, but at a very high installation cost.

It's already been said, you get the most bang for your buck with insulation. Walls not need to be torn open, I'm pretty sure it can be blown in thought holes made in the wall a few inches in diameter.

My family owns an apartment house with a foundation from the 1800's and the main structure built in 1930 in NY state. When the 40 year old oil boiler blew up 9 years ago I designed a replacement system using 2 smaller boilers and better controls, outside temperature reset, etc. At the time oil was still cheaper than gas (as it had been for nearly 100 years). Without changing anything in the building itself (which has 90 radiators) the oil consumption was cut in half. Then fracking happened and the price of gas plummeted. Last year we changed the not so old oil boilers for gas boilers. This cut the cost of heating in half again (the building always had gas for cooking).

Bottom line, gas is by far the cheapest method of heating, but there are still lots of things that can be done to reduce costs even with oil.

Modern mini-split heat pumps are amazing. Last autumn I put three single-head ones in our house. (Mitsubishi 9k BTU as it happens)

I used 1/2 a tank of oil ( ~ 100 gallons) and about a cord of wood, vs. previously using around 2 tanks of oil (500 gallons) and 4 cords of wood. Okay, granted the electric bill was $200 in Jan and Feb, but that's still less than buying normally priced heating oil.

We had one night where the heat pumps shut down because of reaching their low temperature limit, but it was -25F that night.

They're air conditioning as well, so we should be quite comfortable this summer. Highly recommended!

BTW, once the pumping costs are figured in for geoexchange systems, they're in the ballpark of operating costs with air-source minisplits at moderate temperatures, but installation costs for the minisplits are far, far lower.

anticitizen13.7 said:

Hmm.. I didn't know that insulation could be installed so easily. I do not know a whole lot about houses. I will investigate the walls of my home to see what can be done.

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You can do plenty without getting into the actual heating system... double or triple glazed windows in good sealed frames, low-E, argon, heat mirror... you lose an amazing amount of heat through old windows. And add unwanted heat in the summer.

Your attic space is the first place to look at insulation improvements. Most heat goes up and out and it's easiest to get insulation blown into the attic space (typically).

Walls may also allow for more insulation, especially if it's older construction, the walls will be 4" and probably insulated somewhat already. But you might find they could be improved. Depending on the exterior treatment of the house, you might be able to add insulated siding. If you have 6" walls, it's a newer home and should be up to a decent standard already.

And of course, weather stripping - that's an easy one!

Those are all things that will reduce your heating costs no matter what you use for heating... and that's really the first goal - you don't want to waste energy, whether it's oil or electricity.

Sun exposure can produce much direct heating, but for some reason you do not mention this. A big old house can offer ideal spots for big high-e windows to create hot rooms. You can build inexpensive solar collectors if sun hits your ground level perimeter. Forget resistive heating.
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As an owner of an old house (1814) I'd suggest the first thing would be fixing leaks, mainly windows and doors, then good tight storm windows and doors, then attic insulation, and finally wall insulation. As for heating methods, electric resistance heating is extremely inefficient if you consider the cost and environmental problems with generating electricity. I'd expect a modern low temp forced hot water gas fired system to be much more environmentally friendly than electric heating.

I don't know what part of the country you are in but would solar hot water heating be an option? You'd probably need a supplemental heat source as well for those cloudy days. Where I live, we have over 300 days of sunshine per year...but I recently read an article about someone in Maine heating their home that way.

MorrisonHiker said:

I don't know what part of the country you are in but would solar hot water heating be an option?

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With the exception of areas that NEVER see freezing temperatures and a black barrel on the roof works for heating water... Since the cost of solar PV modules has fallen to ~$0.70/w PV + heat pump makes more sense economically than any type of solar hot water heating.

You can get a heat pump hot water heater for ~$1k at a Lowes. That water heater will use ~1800kWh/yr with a family of 4. Even in Seattle you can generate ~1800kWh/yr with 1.6kWp of solar PV. Anywhere else in the country it's more like 1kWp. So for ~$2k you can generate 100% of your hot water from the sun with PV + a heat pump.

.... Try getting a solar hot water system for ~$2k....

We make a lot of money undoing and redoing what people have spent good money doing wrong. It's kind of a bummer coming in after they've spent a boatload of money and are thoroughly frustrated and defeated - on the other hand it's nice to fix things they'd pretty much concluded were impossible to fix.

Diagnose, plan, check the plan, implement. As Einstein said - “If I had an hour to solve a problem I'd spend 55 minutes thinking about the problem and 5 minutes thinking about solutions.”

Start with an energy audit including blower door leakage measurement, and possibly duct leakage testing as well. Really understand the weaknesses and opportunities - don't go off half cocked or you will be disappointed.

Depending on where you live there may be programs that can help you keep your process in order.

There are a lot of good points in this thread. I especially like the idea that your local utility may have a program (mine does) where they will come out to your house - for free - and suggest areas to reduce your energy use, and give you an idea of the cost efficiency of each. That seems like a great place to start.

I bought a pre-built net-zero-energy house, so I didn't do all the research myself. But it has an electric Daikin Altherma air-to-water heat pump. They have models with COP up to 4.4 (mine is a fairly big one that is "only" 4.0). As others have noted, the practical efficiency will vary a great deal depending on temperatures in your area; in some places there are times of the year where a heat pump doesn't work at all. But the Daikins include a resistive backup heater, and of course your house could have other sources for heat, such as a gas fireplace - if the cold days are few, that may be a reasonable option.

It may be worth trying to find a Daikin dealer near you to ask how it would work in your area. They printed out a many-page document describing efficiency at various temperatures, and graphing the results over a year. It showed how much time the Altherma would spend at various efficiencies, and how often the backup heater would have to get used. It sums up the total use and compares it to alternatives (like resistive electric, high-efficiency NG forced-air, etc) and shows you the resulting energy use, cost, GHG emissions, etc. For my home the Daikin was clearly the best at all of these (though the builder does say it was quite expensive to install; the costs in the graphs are only ongoing costs). I am sure there are other dealers that could do the same; but Daikin is the only one I have personally seen.

The builder (Ichijo; they are Japan's largest home builder, but just getting started in the US) did a lot of cool things to make the house more energy efficient. The insulation is really great; it's not just thicker rolls, but also putting dense foam over all wood in the walls, etc. The house also came with enough PV to cover all electric use for the house - including the Daikin - on a net-zero basis (I added a second PV system to cover the cars). All of this did make the per-SF price of the house pretty high, but it is very efficient (for its size; it's a bigger house than I would have built) and comfortable.

ChadS said:

There are a lot of good points in this thread. I especially like the idea that your local utility may have a program (mine does) where they will come out to your house - for free - and suggest areas to reduce your energy use, and give you an idea of the cost efficiency of each. That seems like a great place to start.

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Not only that, but once you decide on what you want to do, you can get tax credits of 30% for installing solar heat, electric, heat pumps, etc.

This thread got me looking at air source heat pumps. It seems that progress is variable speed compressors has made them more practical in cold climates, I live in MN.

Can anybody point me to a calculator where I can understand therms compared to kwhs at a given temperature?

I want to look at my gas bill, and understand at an average given temp how many kwhs it would take to equal the number of therms I consumed.

Example (making up numbers)

In December the average temp was 18f, 100 therms were consumed, an air source heat pump would need X number of khw's to provide the same amount of heat.

Thanks

Edit: I have solar and can buy 100% wind energy if I need more electricity, the idea of going 100% non-carbon is exciting to me.

Evbwcaer said:

In December the average temp was 18f, 100 therms were consumed, an air source heat pump would need X number of khw's to provide the same amount of heat.

Thanks

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1 therm = ~29kWh

@18F you're looking at a COP of ~1.25... so your heat pump would consume ~2320kWh providing 100 therms of heat.

Evbwcaer said:

This thread got me looking at air source heat pumps. It seems that progress is variable speed compressors has made them more practical in cold climates,

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I have experience with these too. One building has a Carrier Greenspeed system which is a variable speed compressor and stepper motor operated expansion valve. It works "better", but with the intense winter we had here in NY state it still spent a good part of the time on the resistive (aka expensive) heat.

Without question if gas is available that is the way to go. Unless you are intentionally designing a extra low polluting heating system, which could have a low operating cost, but will have an extremely high installation cost.

1 therm is very close to 100 CCF which is also very close to 100,000 BTUs..

In Europe most people uses heat pumps. Using any kind of combustion of gas or oil is unheard of, at least since the 90s in Sweden anyway. Modern heat pumps work below -20 C, sure not as efficient but they are sized to deal with this and there is always an auxiliary electric heating element. In cities, there is always a centralised heating network installed, so you only pay a small fee every month for heating . The actual heat is generated by a centralised plant, burning renewables. Some individual homeowners have wood-pellets burners, but these are a pain because they require manual cleaning from deposits. Still the installation and running costs are low.

Go for a heat pump if they are available in your area (preferably a geothermal setup) , it's great because they are almost maintenance free like an electric motor and has an extremely low operating cost, plus depending on the model they often cool in the summer.