We finally got to zero! Welcome to my adventure in cutting fossil fuels at home! Read the other posts in the series here:
Part 1: Reducing Heat Demand
Part 2: Converting Hot Water Tank to Electric
Part 3: Converting Gas Range to Induction
Part 4: Upgrading Central AC to Heat Pump
Part 5: Summary and Discussion
13,262m3 – this is the magic number at which my fossil gas meter finally stopped moving! I reduced heating demand, replaced my gas fired hot water tank, replaced my gas fired range, and finally installed a heat pump. It took 11 months since moving in to the house to go from a full on gas-hog to zero fossil fuels. I try to stop and think about what this 13,262m3 means – 60.5 tons of CO2 emissions (this includes methane leaks in gas production and distribution) since the meter was installed probably 10-15 years ago. I think of the potential for huge reductions in fossil fuel emissions if it was more widely known that it is not that difficult or expensive to heat a home without fossil fuels. I think of the massive benefits to public health, the economy, and our future in doing so. Perhaps this could be a whole other post in itself – so let’s get to talking about heat pumps!
Mike’s Top Heat Pump Points
If you don’t have enough time to read this whole admittedly long post, here are my key takeaways from the project:
What is a Heat Pump?
A heat pump is a mechanical system that uses electricity to move heat from one location to another. A fridge is a heat pump that transfers heat from inside the fridge to outside to keep food at an appropriate temperature. Your air conditioner is a heat pump that transfers heat from inside your apartment to outside to keep you at an appropriate temperature. Please check out this Wikipedia page if you want to read more about the inner workings of heat pumps and the refrigeration cycle.
When you think about heating a house with heat pumps, you might imagine a very expensive system with pipes in the ground, using the earth as a form of seasonal storage. This is known as a ground source heat pump (GSHP) and is indeed very expensive to install, which is why I didn’t consider it. A heat pump that pulls heat from the air is known as an air source heat pump (ASHP). The reason for past focus on GSHP systems for decarbonization is that ground temperatures stay relatively consistent throughout the year so it’s easier to pull heat out of it compared to freezing winter air. However, in the last ten years, several technical improvements have enabled ASHPs to work in extremely cold temperatures. For example, the heat pump I purchased can operate down to -27C. This doesn’t necessarily mean it will provide 100% of the heat load of your house at that temperature – depending on heat loss of your home, you may need auxiliary heat (such as electric or gas furnace, baseboard heaters, etc) at extreme low temperatures because heat losses could outstrip heat production from the heat pump. Check Part 1 of this series for ways to decrease heat loss. I won’t go into excruciating detail on it, but some of the advancements that enable low temperature performance include: thermostatic expansion valves, inverter motors, and improved coil and tubing design. The bottom line is ASHPs work at low temperatures. For the rest of the post, I’m going to refer to ASHPs as just “heat pumps.”
Part of my inspiration for going fossil free with a heat pump was that my mom had already done it at her house in Tweed, Ontario. She did it because she was getting tired of hauling wood, which she previously used for heating, and because heating with fossil fuel (propane stove) was going to be about 3 times as expensive as using a heat pump. Her house doesn’t have a furnace, so she installed a ductless mini split system, with the indoor fan integrated with the indoor coil. Given that Tweed gets colder than Toronto and her house is leakier, I was pretty sure I could do something similar at my house. She supplements the heat pump with electric baseboard heaters when it gets below -20C. I had also convinced my landlord at my previous apartment to install a ductless mini split heat pump system to replace a 30 year old window shaker AC. That heat pump displaced electric baseboard heating, saving lots of electricity, and worked great all winter.
Here’s my awesome mom with her heat pump. Looks to me like it works in the cold!
What did I do?
I had a semi-old (~12 years) central AC unit that was nearing the end of its life, making lots of noise, and cooling inefficiently. I probably could have got a few more years out of it with some repairs, but was very eager to not burn fossil fuels this winter.
My old, low efficiency noise maker
Remember, an AC unit is a heat pump that takes heat from inside and rejects it outside. That’s why you feel hot air blowing out of the condenser outside when it is running. A reversible heat pump does the same thing, but it can also reverse the process taking heat from outside and rejecting it inside. In winter, the heat pump has cold air blowing off of it outside and the coil in the furnace is hot. In summer, the heat pump has hot air blowing off of it outside and the coil in the furnace is cold. So, the project I did was very similar to a normal AC replacement. I replaced the outdoor unit with a heat pump, plus replaced the refrigerant lines to the furnace and replaced the coil in the existing furnace in the basement. Here is a schematic of the project:
Left image: Previous AC only system, Right image: New heat pump system
Here is the before and after picture:
As you can see, the new heat pump is a bit bigger than the old AC. Heating demand is higher than cooling demand in Toronto, so I went from a 2.5 ton AC to a 3 ton heat pump to be confident I would have enough heat (ton is a measure of cooling/heating capacity typically used for air conditioning). The heat pump is also raised off the ground in order to make sure it stays clear of snow. This model is slimmer than the old AC unit, so I gained a bit more room to schlep the garbage cans to the curb.
The cost of the installation was $4,200+HST. According to the contractor, the cost of installing a like-for-like AC replacement would have been $3,500, so the incremental cost to go with a heat pump was only $700. I double checked this info at HVAC industry website furnaceprices.ca and found similar cost ranges.
Cost of installing a central air conditioner. Credit: furnaceprices.ca
This fairly modest incremental cost is something very important to keep in mind if you have a central AC that is nearing end of life. You can drastically slash CO2 emissions at your house (even if you haven’t taken heat loss mitigation measures) at modest added cost by installing a low temperature heat pump when your AC needs to be replaced. Get the contractor to set the heat pump as the first stage of heating and the furnace as the second stage, only to be activated if the heat pump can’t keep up with the heating demand.
This is exactly what I did, although I have not needed any gas. I have five hours of data where outdoor air temperatures were between -12 and -15C, with the heat pump putting out an average of 21,000 BTUs during those hours and running about 66% of the time. This suggests to me that there is room to accommodate lower temperatures. Given that Toronto historically averages only 68 hours per year below -15C, I am getting more and more confident in cancelling my gas account altogether and maybe picking up some plug in radiators for emergencies (this would probably be a good idea regardless in case of fan/furnace failures). Let me also preempt the idea that a gas furnace is somehow impervious to blackouts. With electronic ignition, various control panels, and electric blower fan, I would be just as cold as with a gas furnace as I would be with electric heating in any sort of blackout situation. The thermostat pictured below shows outdoor temperature of -11C and steady at 20C inside. I was hoping to get some temperatures down to -20C before writing this blog post, but alas it appears not to be for this winter.
Sure bud, but what about your electricity bill??
The whole point of this series is to attempt to prove that homes can be electrified in many parts of Canada at relatively low upfront cost and with low impact to utility bills. Everyone knows electricity is more expensive than gas on a per unit basis, but what often isn’t clear is that heat pumps are VASTLY more efficient than fossil fuels. Typically, the heat energy transferred by a heat pump is several times higher than the electrical energy input, known as the Coefficient of Performance (COP). I calculated my average COP for the month of January to be 2.3, meaning for each 1 kWh of electricity the heat pump transferred 2.3kWh of heat into the house. In terms of efficiency, the heat pump was 230% efficient that month compared to 94% for my gas furnace. If you are interested to see how I did this calculation, you can check the “Calculations” section at the end of the post for an explanation. If you are wondering how it is possible to achieve over 100% efficiency, you can read more about the refrigeration cycle on Wikipedia.
Let’s take a closer look at my energy consumption in January 2021, during which I used about 1020kWh. I can estimate how much of this was from the heat pump because during Sept-Nov (before heat pump install) my AC was off and my average electric consumption was about 470kWh. If I subtract that from my January total, it leaves around 550kWh consumed for heating. I know how much gas I would have used because I can just scale last year’s consumption according to this year’s weather. That amount based on the weather this January is about 120m3. The energy content of 1m3 of gas is 10.3kWh, so my total heating energy consumption would be 120m3 x 10.3 kWh/m3 = 1,244kWh.
To summarize, heating with fossil fuel consumes more than double the energy compared to heating with a heat pump. So next time someone tells you natural gas is “efficient” make sure you mention heat pumps and dispel those fossil myths! The next question is: does the superior efficiency make up for the higher cost of electricity?
Let’s look at the numbers. The incremental cost of electricity is about $0.141/kWh for me and gas is $0.329/m3. This means in January my added electricity cost of heating with the heat pump was $35. In December, it was $12, and in February if weather trends continue it will be $36. But wait! I’m still paying a $25 per month account fee for gas even though I’m using zero gas. So that will be an extra $25 per month savings *all year* as soon as I cancel. I am also expecting to save around $40 of electricity in the summer from more efficient air conditioning. As an aside, I got lucky this year with the COVID-related electricity subsidies, so the actual added cost in January and February ended up being less than $10 even with paying the gas account fee but I’ll ignore that since it is hopefully a one-time event. Let’s project the typical electricity costs over an average year to get the full picture.
|Added electricity cost||$385|
|Saved gas cost||$211|
|Saved gas account charges||$295|
|Saved air conditioning electricity cost||$40|
|Annual cost if I had to keep gas account||$135|
|Annual savings if I cancel gas account||$160|
Annual Heating Costs/Savings Based on Last 5 Years Average Toronto Weather
Interestingly, the cost of the gas account fee is higher than the actual gas itself, so being able to cancel my gas account becomes the key factor determining whether there will be a net cost or savings. Either way, we’re talking about the cost of getting takeout lunch once a month. Considering the incremental cost of the heat pump over a standard AC replacement was $700, the payback with cancelling my gas account is less than 5 years. Keep in mind, this is for my house that was consuming around 700m3 per year of gas for heating. For houses consuming significantly more heating energy, the savings could be worse because the fixed savings of the account fees become overshadowed by the difference in unit cost between electricity and gas. As a point of reference, if I assume my house had double the annual heating load, the annual added cost of heating would be $310 with keeping the gas account and around break-even with canceling the gas account. Bottom line: you can save money by heating with a heat pump and if you keep your gas account it will probably cost you $10-20/month extra.
CO2 Emissions Reductions
As I mentioned in previous blogs, fossil fuel combustion is a public health crisis that is imposing huge costs on society. As a person with the knowledge and means, I felt an obligation to do my part to cut my fossil fuel consumption. I wanted to do it in a way that was as inexpensive as possible to try to be an example that can be easily replicated. More important than the economic considerations above, getting as many people off fossil fuels as quickly as possible is mandatory to secure our own and our children’s futures.
Accounting for methane leaks during gas production and supply, this project has eliminated 2.92 tons of CO2 emissions annually at an incremental cost of $700, assuming I already needed to replace my AC. For an estimated equipment life of 15 years, this works out to $15 per ton, which is lower than the current carbon tax in Canada. It seems to me that there is potential for the government to create an incentive program for this type of project to reduce emissions at a cheap rate. For more detailed GHG calculations, see the Calculations section at the end.
A key source of climate warming pollution is refrigerants. The refrigerant in my heat pump, R-410A, is 2088 times more potent a global warming agent than CO2. So even though there is only 3kg of refrigerant in this heat pump, if it leaked it would have the same effect as 6.4 tons of CO2. In most cases, leaks only happen at end of life when equipment is being removed/disposed of. In Canada there are stringent requirements for capture and destruction of refrigerants to try to prevent their release into the atmosphere, but it is still possible that leaks could happen. R-410A is commonly used in air conditioners (including my old one), so going with a heat pump wouldn’t increase refrigerant leak risk over a standard AC replacement. I am hoping that more eco-friendly refrigerant options are available by the time I need a new heat pump. High global warming refrigerants are undergoing scheduled phase outs mandated by the Kigali amendment of the Montreal Protocol.
Air Temperature: The air coming out of the vent isn’t as hot with the heat pump. The heat pump coil produces between 30-36C air, whereas the gas fired furnace produces air around 50C. This has a couple of implications. First, it takes a lot longer for the heat pump to make up temperature setbacks. Last year, I programmed my thermostat to set back temperatures to 17 or 18C over night in order to save energy. Getting back to 20C in the morning with a gas furnace took maybe half an hour, but I found the heat pump running for up to 4 hours to try to bring the temperature back up. Usually, the morning is the coldest time of day, so this made the heat pump work even harder to pull heat from outside. I found the heat pump would run about the same amount of time in the morning that it was off for overnight, meaning that the savings from temperature setback were basically nil. I decided to run at a fixed setpoint of 20C and found the overall run time didn’t change significantly. Bonus! With a fixed setpoint, nobody complains about freezing at night anymore. The second implication of lower output temperature is that you don’t feel that burst of super warm air blasting over you when the furnace cycles on. At lower heat pump temperatures, when the fan is running it is more a feeling of subtle air movement that can have a slight cooling effect. Luckily it’s winter, so you are wearing a sweater already.
Measuring output temperature with meat thermometer
Defrost: When you are heating, the heat pump coil outside is considerably colder than the outside air (this is how it picks up heat). When the humidity outside is high enough, this can cause frost to form on the coil. The heat pump can automatically detect when frost builds up and runs a defrost cycle. I don’t have to do anything other than know that there will be some water melting off the unit every once in a while. Ideally, you can locate the unit somewhere that the water drains in a convenient location, such as over gravel or soil. In my case, I have very limited outdoor space and it discharges over concrete so I have to be aware of putting salt down sometimes to combat ice. At first, I thought this would be pretty annoying, but it turns out that the defrost didn’t really happen very often and it was fairly predictable that it would occur at mild temperatures between 0 and -5C especially when it was raining/snowing (ie high humidity). At lower temperatures, there just isn’t enough moisture in the air to cause frost to occur. I tracked the number of defrost cycles in the first 3 months of operation and there have been about 23 cycles (about 2 per week). I took a video of the unit defrosting to give you an idea of how much water is involved.
Electric panel upgrades: The beauty of swapping this system for my old air conditioner is that I did not need to pay for any costly electrical upgrades. I used the feed on my existing 100 amp panel that was already there for the air conditioner. Because I’m using an existing circuit, this means that I am also imposing no increased load on the utility grid. I am using more electricity in winter than otherwise, but the grid was already designed to support that power because it was designed with the power needed for air conditioning in mind. This means everyone can do this project without the utility having to build new electrical infrastructure.
Air Pollution:As shown in the picture at the top of the page, gas furnace exhausts now seem to be exclusively located at child breathing level, blasting fumes out all over the streets and sidewalks. If more people were able to make the switch away from fossil gas, our neighborhoods would be much nicer places to be. Air pollution caused by fossil fuel burning was found to cause 8.7 million premature deaths globally in 2018.
Noise: My old air conditioner was an embarrassment that you could hear rattling half way down the block. The heat pump still makes some noise, but it isn’t significantly louder than that whine you hear from the furnace exhaust when the gas is burning. Big improvement overall and my neighbors will probably thank me in the summer.
Thermostat Compatibility: I have a compatibility issue with my thermostat (Ecobee). In order to run as a heat pump, it wants to control the reversing valve (the device within the heat pump that switches between heating and cooling). However, the heat pump I got does that control on its own depending on whether it receives a signal for heating or cooling. The contractor decided to try to trick the thermostat by setting it up as a two-stage furnace, running the first stage to the heat pump and the second stage to the furnace. Unfortunately, in this configuration, the thermostat kept calling on the second stage too soon and gas heating was getting enabled for no reason. This is likely because the heat pump, supplying lower temperature air than a gas furnace, was taking longer than expected to reach the setpoint. Since it assumes both stages are gas, it doesn’t provide the option to delay the second stage further. After many conversations with Ecobee that went in circles, I just unplugged the control wire for the furnace from the thermostat. I figured I would just plug it back in if I needed it (I did not need it this winter). So I guess the takeaway is to grill your contractor a bit about how the heat pump will be integrated with your thermostat. If you are doing a full electric furnace/heat pump conversion it will probably come with integrated controls.
Here are some fun charts from the data I collected:
This chart shows the monthly absolute heating energy savings for the first three months of operation (Feb estimated). Baseline gas energy was converted from m3 to kWh to make the comparison. Once again, fossil fuels = waste!
Sorry for the Fahrenheit units, but those were the ranges provided by the heat pump manufacturer, so they ended up filtering through all my charts. As you can see, most of the defrost cycles occur in the ranges just below the freezing mark. This has the effect of lowering the average heat output because a) frost decreases heat transfer, and b) the defrost cycle actually blows cold air into the house for a couple of minutes. These brief cold air bursts were picked up by my temperature logger that I installed in the supply air stream. Interestingly, the unit never comes close to supplying its rated capacity of 3 tons (36,000BTU/h) on an average basis, but it doesn’t show any reduction in heat output at lower temperatures either. I do have individual readings over 31,000BTU/h, so I suspect the average is lower because the run times are short when it’s above freezing outside. With short run times, a higher proportion of the readings would be during the system warming up and cooling back down, bringing down the average. For example, if I’m reading the temperature every minute and the unit warms up for 2 minutes, runs for an hour, and cools down for 2 minutes, the average output should be accurate. On the other hand, if it warms up for 2 minutes, runs for 5 minutes, and cools down for 2 minutes, the effect of averaging in the warmup time will be greater.
This chart shows a pretty clear correlation between equipment run time and outside air temperature. Based on that trend it looks like it could get quite a bit colder and still provide the heat I need.
This chart shows the heat pump performance versus the data supplied by the heat pump manufacturer. As mentioned above, I think the average BTU/h readings at warmer outside air temperatures are lower than spec because the run times are so short so I’m not capturing as many readings at full heat output. For the temperatures around the freezing mark and slightly below, the average is also lower due to the impact of frost, which may not have been accounted for in lab testing. It is very encouraging to see that for the lowest outside air temperatures, when it really matters, the heat pump is performing very close to the designed output.
Look for a future blog post summarizing my overall results and thoughts on the “Cutting Fossil Fuels” series. I will also be posting about some innovative waste heat recovery projects at UHN that use heat pumps to boost efficiency. Thanks for reading and feel free to reach out with any questions on cutting fossil fuels or to share your success stories with your own heat pump. Let’s kick the fossil fuel habit together!
COP = Energy output/energy input
I know my energy input based on my utility bill analysis. For January, this was 550kWh. For energy output, I used a formula that is familiar to any HVAC engineer:
Energy (btu) = 1.08 x air flow (cfm) x temperature difference (degrees Fahrenheit)
I know the air flow of the fan is 945cfm and the return air temperature is logged by my thermostat, so all I needed was the discharge air temperature from the heat pump coil. I purchased a temperature logger and installed it in the nearest outlet vent to the heat pump and now had continuous monitoring of the heat pump energy output. Next, I averaged all the btu readings over the month and multiplied by the hours of operation to get btuh. To convert btuh to kWh, divide by the factor 3,412 btuh/kWh.
GHG emissions of natural gas combustion are estimated to be 4.56 kgCO2/m3 if you account for fugitive methane leaks during production and delivery. My annual gas savings are estimated to be 640m3 based on eliminating all gas consumption using the average weather profile of the last 5 years. Multiply those and you get 2.92 tons.
To complete the GHG emissions savings calculation, we should account for the fact that the grid is not 100% carbon neutral in Ontario. In my case, I purchase 100% renewable energy from an electricity reseller, so I have some peace of mind whether or not utilities or governments decide to make the grid dirtier. The last year I could find data for was 2019, showing Ontario’s grid emissions factor to average 40.5gCO2e/kWh and only 6% of production from fossil fuels. However, high fossil gas plant usage occurs in the summer. Looking at hourly data, the average emissions factor during heating season is 28gCO2e/kWh. My estimated annual heating consumption is 2,734kWh with the heat pump, representing 0.08 tons of CO2. Keep in mind these emissions factors could change depending on various factors. Subtracting this from the savings above, the overall savings in Ontario for the project would be 2.84 tons per year if i didn’t buy renewable power. It’s worth noting emissions would still be lower even if electric generation was more heavily weighted towards fossil gas. Once again, this is because heat pumps are so much more efficient at heating.
The difference in embedded carbon between an AC unit and similarly sized heat pump would be negligible as the only real difference is the addition of a reversing valve.