Comparing energy usage: 1 year of gas heat vs. 2 years of heat pump

Hot_water_fan

After moving in, I spent about 3.5 months with an 80% efficient furnace before replacing it with a 24kbtu/h cold climate heat pump, so I figured I'd share my experience. Here are some notes:

1. The table below shows the entire gas and electric usage for the house for the same time period, both before and after the replacement.
   
2. Energy costs are included, but don't line up perfectly with the dates, as gas prices change a lot here - supply, distribution, misc. variable fees, etc.
   
3. It is roughly 30% cheaper to use electricity for heat here.
   
4. The therm factor is what the utility uses every month to adjust the measured usage to the usage they charge for. It's usually 0 - 10%.
   
5. The coldest temp experienced was 8 degrees Fahrenheit.
   
6. The COP is estimated, not measured. Take it as such.
   
7. I'd expect the seasonal COP to be higher: in 2022, there were 800 heating degree days after 2/18/22, with a higher average daily temperature than the 11/1 through 2/18 period.
   
8. We had guests in December 2022 who used an electric space heater to heat a bedroom to 80 degrees, while we kept the rest of the house around 70, so there's a bit of extra usage for that period.
   
9. The heat pump does not have electric resistance strips installed. It has kept up in all weather.
   
10. I've chosen to have the blower fan operate continuously for the heat pump, but didn't for the furnace (too loud).
    

Let me know if you have any questions!

ChrisJ

A whole 3.5 months eh.

Hot_water_fan

@ChrisJ Well AC is more important to me than a furnace .

Hot_water_fan

Hi @ron,

Right now, electricity is $.1457/kwh and gas is $1.574 per therm. I tried to show that the COP of the heat pump is around 3 for this time period. That means the $/MMBtu for the heat pump is: $14.23 and the gas is $19.68. That's a 28% cost savings.

Long Beach Ed

On Long Island, I pay $ .36/kwh for electricity vs. your $ .14, with "delivery and taxes".

I pay $1.46/therm for gas vs. your $1.50.

My gas equipment has a life of fifty years; HVAC electric equipment has a life of fifteen. Gas equipment service and repair costs are negligible. Scorched air can't compare with hydronic comfort.

Anyone mention the back up electric resistance heating?


It would be ludicrous to heat with electric hot air here.

Hot_water_fan

On Long Island, I pay $ .36/kwh for electricity vs. your $ .14, with "delivery and taxes".

I pay $1.46/therm for gas vs. your $1.50.

My gas equipment has a life of fifty years; HVAC electric equipment has a life of fifteen. Gas equipment service and repair costs are negligible. Scorched air can't compare with hydronic comfort.

Anyone mention the back up electric resistance heating?


It would be ludicrous to heat with electric hot air here.

Obviously, prices will be different! No argument there. I don't understand the relevancy of equipment life - AC is happening either way. The furnace could last for 1000 years and it wouldn't matter. Nor is hydronic relevant - I had a furnace before. Most Americans have forced air.

No backup electric resistance - didn't need it, handles single digits temps just fine.

Hot_water_fan

is your $0.1457 just the generation portion? If so then your electric number is grossly low. Last time I remember my electric bill, in CT, the lowest generation ever was as low as $0.07 (years ago) and is now somewhere around $0.15 or $0.20 per kwh but that's just for generation. The transmission is like $0.30 per kwh or higher and is additional, so you really have to take your total electric bill dollar number that you pay and simply divide it by the kwh number. Maybe minus the FCC surcharge this, climate change surcharge that, that's added on which might be significant. Wanna say last time I looked, and that was years ago when I recognized what's really happening how they deceive you with marketing just the $0.1457 as the generation charge and making no mention of the transmission add on, we're all like $0.40 per kwh when the money comes out of your pocket.

No, fortunately $.1457/kwh is my all-in rate, which is about average for the US. New England has eye watering electricity rates while we don't, and I suspect it's because of our high AC penetration. My transmission and delivery rate is $.05 $.038/kwh - a lot of juice flows across the wires, so utilization is high. It works in the other direction - gas delivery charges are high here.

Steamhead

Hot_water_fan said:

............ gas delivery charges are high here.

Where's "here"?

Hot_water_fan

@Steamhead we're neighbors! BGE.

Hot_water_fan

@ron that's right

jumper

Any preference comfort wise?

Hot_water_fan

Any preference comfort wise?

The heat pump is more comfortable by a huge margin. However, I doubt it's because it's a heat pump. Being correctly sized and being variable speed is great - it's silent, while the furnace wasn't. It can maintain a setpoint without overshooting, the furnace couldn't. For my heat loss, they don't make furnaces that can provide these features. If someone had a true 60kbtu/h load, then the differences would probably vanish. Probably the same if a small, modulating furnace was on the market. The heat is extremely even - I've lived in several homes with boilers and cannot tell the difference. Maybe others can.

ChrisJ

There are 2 and 3 stage furnaces now

Hot_water_fan

There are 2 and 3 stage furnaces now

Agreed - but they're often too big for homes. Sometimes low stage exceeds the heat loss!

Steamhead

Hot_water_fan said:

@Steamhead we're neighbors! BGE.

Hot_water_fan said:

No, fortunately $.1457/kwh is my all-in rate, which is about average for the US. New England has eye watering electricity rates while we don't, and I suspect it's because of our high AC penetration.

ISTR our electric rates go up in the summer mostly because everyone uses A/C. How long will it take for them to keep them high in the winter to take advantage of an increasing number of heat pumps?

Long Beach Ed

I don't understand the relevancy of equipment life

I have a friend who paid $ 9000 for his mattress. Now he tells everyone he knows that it has changed his life; that it's the best decision he ever made.

Sorry my friend: Equipment life matters. Comfort matters. Operating costs matter. Natural gas powers my electric plant, so where's the benefit? I want the most basic technology with the longest, most reliable service life at the lowest operating cost.

ChrisJ

Long Beach Ed said:

I don't understand the relevancy of equipment life

I have a friend who paid $ 9000 for his mattress. Now he tells everyone he knows that it has changed his life; that it's the best decision he ever made. Sorry my friend: Equipment life matters. Comfort matters. Operating costs matter. Natural gas powers my electric plant, so where's the benefit?

The power company wants to sell more electric to consistent predictable loads.  That's the only benefit and it's not your benefit.

Steamhead

Long Beach Ed said:

........ Natural gas powers my electric plant, so where's the benefit?

Exactly- the process of producing electricity from fossil fuel, and getting it to the customer, is something like 30-35% efficient. How does this reduce greenhouse-gas emissions?

Hot_water_fan

@Steamhead and @Long Beach Ed we are going astray, but I assure you that a heat pump COP of 3 paired with a 50% efficient combined cycle gas plant is much more efficient that a furnace with a COP of .97. This is the simple reality for American gas generators. For nuclear, efficiency is lower, but the emissions are less, if that’s important to you. 

Sorry my friend: Equipment life matters. Comfort matters. Operating costs matter. Natural gas powers my electric plant, so where's the benefit?

There’s a point where equipment life doesn’t matter - think of a car. Some people keep their cars for 25 years but 95% probably don’t. Same with a furnace - 20 years is great! 50 years? Maybe I’ll be dead or somewhere else. All equipment would last 50 years IF people were willing to pay for it, but people have other priorities. I’m not going to pass judgement on someone who accepts a shorter furnace lifespan for something else they deem more important. This applies to all sorts of things: fridges, roofing choices, toasters, light bulbs, etc. 

Obviously, operating costs for this situation favor the heat pump. Other places they won’t. I’m never going to argue that point! 

Comfort is subjective. I find this heat pump much more comfortable than the furnace it replaced. I’m just one person and this is just my opinion. The next level thinking is: are customers willing to pay for higher levels of comfort, of whatever form. Can we build value that way? I hope so. 

Hot_water_fan

ISTR our electric rates go up in the summer mostly because everyone uses A/C. How long will it take for them to keep them high in the winter to take advantage of an increasing number of heat pumps? 

Good question! I guess we’ll see. I could see benefits to electric heating loads - I added about 1900kwh per year of demand with the heat pump, but it’s well spread out - my peak hasn’t changed compared to the summer. That’s got to be appealing to a utility trying to maximize the kWh moved over their wires. So maybe the generation increases some and the distribution decreases some. Sounds like BGE is doing just fine, even in the summer, compared to New England. I trust their incentives to figure out ways to sell electricity. 

hot_rod

That is the point to buying power in real time. Mid day on a mild summer day they may drop rates if their generators were geared for a hot day, high AC load That isn’t going to happen.
In some areas your meter would know that rate drop and you might load up a buffer tank with hot or chilled water at 6 cents instead of 14 cents
or load your sand bed😂

Then again they can brown or black you out if loads over run their generating capacity. Hard to outsmart the electricity utility. Especially if you only have one option, them.
,

ChrisJ

3.5 months of one fuel on one system isn't near long enough to be relevant.  HDD or not.

That's my opinion anyway.

fentonc

Why wouldn't it be enough? 3.5 months is more than enough to get a solid measurement of heat loss for the structure in terms of BTU/HDD-hr. The HDD might vary from year to year, but that number won't unless the structure changes significantly. The other (mostly-constant) metric of interest is what average COP his heat pumps can achieve (which is based on location, model(s) and design), and what COP/efficiency his furnace was achieving. Besides those two things, everything else is just chatting about commodity prices which are extremely location and time dependent, and no one can predict future prices. With those two numbers, you can at least tell if one or the other *would have been* cheaper in a given month/location.

hot_rod

Having any accurate actual data is better than all the speculation surrounding that type of equipment.

Hot_water_fan

3.5 months of one fuel on one system isn't near long enough to be relevant.  HDD or not.

That's my opinion anyway.

It’s hourly data, summed up the daily level by me. It caught cold weather, don’t know what else I could do. Cold is cold  . 

Hot_water_fan

@fentonc bingo, I considered leaving the cost data out because it’s only relevant to others in my utility area and can be too much of a distraction. Obviously it works great for me, but not every other person. The COP is the important part because it’s reasonably transferable to people outside this utility. Trading ~1900kwh for ~240 therms is efficient! 

ChrisJ

Hot_water_fan said:

@fentonc bingo, I considered leaving the cost data out because it’s only relevant to others in my utility area and can be too much of a distraction. Obviously it works great for me, but not every other person. The COP is the important part. Trading ~1900kwh for ~240 therms is efficient! 

How many therms were used to create that 1900kwh?

Hot_water_fan

@ChrisJ good question, probably about half that if PJM was 100% gas. It’s clearly not, about a third is nuclear, a third gas, then coal and everything else. Looks like .8 lbs of CO2/kWh for November ‘21 through March ‘22. So about 45% less CO2 than burning gas directly in the existing furnace. 

hot_rod

There is a bit of energy required to get the NG to your doorstep also, compressor stations every so many miles of pipeline. Those don’t run on holy water😂
Imagine if the backup generator is running on diesel😳 Diesel, to electric motor to compressor.

Maybe those copper wires aren’t so bad after all?

ChrisJ

hot_rod said:

There is a bit of energy required to get the NG to your doorstep also, compressor stations every so many miles of pipeline. Those don’t run on holy water😂 Imagine if the backup generator is running on diesel😳 Diesel, to electric motor to compressor. Maybe those copper wires aren’t so bad after all?

So...
The delivery to the power plant runs on holy water?

yesimon

ChrisJ said:

How many therms were used to create that 1900kwh?

Based on the heat rate for natural gas
https://eia.gov/electricity/annual/html/epa_08_01.html, 7700BTU per kWh generated, which translates to 146 therms. Add on 5% for transmission losses equals 155 therms, quite a bit below 240 therms burning it at home.

The carbon emissions side is even more lopsided. The current generation mix is 0.855 lbs CO2/kWh https://eia.gov/tools/faqs/faq.php?id=74&t=11, which translates to 1700 lbs CO2 with the heat pump, compared to 2880 lbs CO2 burning 240 therms of gas. This is a 35% reduction in gas consumption, and 40% reduction in CO2 emissions.

On aggregate, heat pump consumers are beneficial for gas customers because they reduce the overall demand and price for natural gas. Make friends not enemies.

pecmsg

I keep seeing a COP of 3 that's fine and dandy except as the outside temp falls so does the COP#'s!
At 30° maybe a COP of 3
At 10° a COP of 15 or 20
At 0° a COP of maybe 10 or less.

My point is much more information is needed. And yes, lifecycle costs should be included!

fentonc

The COP is both equipment and temperature dependent - this is effectively true for gas/oil-fired boilers as well, as their performance can depend significantly on duty-cycle. From an operating cost (and emissions) perspective, looking at the measured average for the entire season seems like the metric you should care about.

My nominally 83% efficient CI boiler is currently averaging 48.7% efficiency for the season, for instance, even if it did manage to break 70% on one really cold day. That measured sub-50% efficiency is what I'm paying for - the tails of the distribution don't have a big overall impact.

Hot_water_fan

We all know COPs fall! If the seasonal COP remains high enough, it doesn’t matter much. 

ChrisJ

Hot_water_fan said:

We all know COPs fall! If the seasonal COP remains high enough, it doesn’t matter much. 

How are you going to compare the two usefully?

A gas / oil boilers efficiency climbs as the outdoor temperature drops.  The heatpump is the opposite.

A lot of heat lost by most boilers ultimately ends up in the living space. Not true with a heatpump.  Yes some lost energy does, but not the efficiency drop.

Hot_water_fan

We have to realize that most heating hours aren’t that cold. People can get a little too fixated on what COP at some 1% temperature is. So seasonal COP vs AFUE is just fine - this isn’t rocket science. Few people will pay for a redundant heating source to save a trivial amount unless it’s extremely cheap to install. 

ChrisJ

Hot_water_fan said:

We have to realize that most heating hours aren’t that cold. People can get a little too fixated on what COP at some 1% temperature is. So seasonal COP vs AFUE is just fine - this isn’t rocket science. Few people will pay for a redundant heating source to save a trivial amount unless it’s extremely cheap to install. 

Where do we have to realize this?

Curious what general area are you in.  If you mentioned it already I apologize I've been sick

Steamhead

@ChrisJ , he's somewhere near Baltimore.

Hot_water_fan

Thanks @Steamhead. The point is the same - worrying about worst case COP isn’t as helpful as seasonal COP. In fact, had I enough panel space, I actually would have installed a non-cold climate heat pump: they seemed more efficient at mild temps, so eating some resistance kWh would have been better, surprisingly. 

ChrisJ

Hot_water_fan said:

Thanks @Steamhead. The point is the same - worrying about worst case COP isn’t as helpful as seasonal COP. In fact, had I enough panel space, I actually would have installed a non-cold climate heat pump: they seemed more efficient at mild temps, so eating some resistance kWh would have been better, surprisingly. 

Ok .
How about International Falls MN?

Still no point?

I just picked 2018 randomly.  I doubt these are record temperatures.

Hot_water_fan

It’s cold there! Long shoulder seasons would help the COP. I won’t run the numbers but obviously there are some places where hybrid systems make good sense. It’s not a binary, we must remember that.