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My electric utility company sent me a graph of my home's electricity usage over time as shown in the picture below. My home beats what the company considers as efficient homes in the neighborhood when the average temperature is below ~50F. As the temperature increases above ~50F my home becomes increasingly inefficient, relatively speaking.

I'm puzzled by this. Can anyone help me understand what part of my house I need to improve? Does this mean that my home's insulation is OK, but A/C system is not? Or, does it mean that heat enters my house easily but does not escape easily, meaning insulation is good in one direction but not the other?

As reference, my house has centralized HVAC. Heating in my home is natural gas. The A/C is traditional, refrigerant-based, with the compressor located in an external unit. Most components of the HVAC system are about 20yrs old.

Thanks.

the attached graph

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  • 69
    Your poor insulation is unseen by the electric utility in winter because you are heating with gas.
    – Ecnerwal
    Commented Jan 9, 2022 at 15:33
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    "similar" likely as basic as "single family homes (or townhomes or apartments - i.e., just the very basic category) in the same zip code (which takes weather out of the equation)".
    – manassehkatz-Moving 2 Codidact
    Commented Jan 9, 2022 at 16:21
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    In a similar (but more controversial) way, some water utilities price based on total usage with a theory of "per person should be 'x'", and then just group all single family homes together, townhomes together, apartments together based on "average people". In my neighborhood there are single family homes (in some cases exact same size all built in the late 1950s) that have anywhere from 1 person (typically a widow/widower living alone) to large families with 8 or even more people. The utilities don't distinguish because (at least in the US) they don't collect data on the number of residents.
    – manassehkatz-Moving 2 Codidact
    Commented Jan 9, 2022 at 16:24
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    This may be as simple as "you have air conditioning, and the average customer does not." With the average temperature topping out at 78 in the summer, you probably live in an area where a lot of people don't bother having AC.
    – Glenn Willen
    Commented Jan 10, 2022 at 6:25
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    I think statueuphemism is right, but another possibility is that you just like it colder than most people. That means you run the AC harder than the average person in the summer, but you run the furnace less than most people in the winter.
    – Nicholas
    Commented Jan 10, 2022 at 16:01

7 Answers 7

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The heating in your home is natural gas. You are not using any electricity to heat your home in the winter.

Therefore, from your electric company’s perspective, you are very energy efficient in the winter by not using much electricity as someone with an electric-based heating system.

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    I think the comparison is with "similar" households in the neighborhood. I'm assuming the utility company has taken the type of heating (natural gas vs. electric), area of the house, etc. into account in this graph. Meaning, this graph includes only homes with natural gas heating. I'm not positive about that, but the graph wouldn't make sense otherwise.
    – Fijoy Vadakkumpadan
    Commented Jan 9, 2022 at 16:09
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    This is 100% the answer. In many (not all) places the electric utility doesn't even know whether you have natural gas or not, let alone whether you use it for heating, hot water and/or cooking. Plus you might have (as many in my neighborhood) natural gas that originally was for heating but where people have switched to heat pumps. Those houses will appear to be less efficient (electrically) in the winter, making the other houses (still using natural gas) look more efficient winter but less in the summer. The only way to truly compare is to compare "same only" or to compare total energy use.
    – manassehkatz-Moving 2 Codidact
    Commented Jan 9, 2022 at 16:14
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    I have worked on a system (commercial/government, not for single family homes, but the idea is the same) that can add up entire energy usage (electric, natural gas, even coal and oil) based on cost and/or energy (BTU) and compute usage per-square-foot. Not that hard to do. But unless your electric utility is also your natural gas utility (it is that way in some places) they're not going to do it. These charts (my local utilities provide similar charts) are based on "what can we provide the customers with minimal development cost and no additional data collection". Sometimes utilities will
    – manassehkatz-Moving 2 Codidact
    Commented Jan 9, 2022 at 16:17
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    @FijoyVadakkumpadan My electric company does not know how I heat my house(free wood heat). My neighbour heats with electric heat. Guess which one is more efficient on a bill. Those graphs only consider electric use, more you use, the less efficient you are. Electric companies don't want to spend the money inspecting every house to make those graphs mean something.
    – crip659
    Commented Jan 9, 2022 at 16:36
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    @FijoyVadakkumpadan This is a display of data they were collecting anyway - Power usage rates. They put it into a cool widget for customers to use, but they're not collecting useful variables like sqft or insulation. Here's a quote from the chart on my provider, which is nearly identical: //Your Home Energy Use Profile is estimated using your usage data, regional residential electricity usage averages and actual weather data.//
    – Turbo
    Commented Jan 10, 2022 at 15:43
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Don't over think this graph. It looks like everyone in the data base has the same heating as you, gas, because if they had electric heat, the points would be much higher than 500 to 650 KWH per month. What this graph really tells you is that you're using more AC than the other people. It could be due to the position of your house in relation to the sun. You could be getting more exposure on your roof and walls due to direct sunlight and require more AC to cool it down. In the winter, you'd still have the direct sunlight that would warm up the house a bit and require less heat because there's not a direct source of cold blowing on your house. If it's sunny and 90 degrees out, the temp on the hood of your car will be much hotter due to the direct source of heat from the sun.If the sun's not out, the hood will be 90 degrees. If it's 0 degrees out and sunny, the hood of your car will be warmer due to the sun, if the sun's not out, the hood will be 0 degrees. You could check your insulation in your attic and walls to see if it's adequate and get your AC checked. We run into the exposure issue all the time down here in South Florida

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    We designed overhangs & balconies to provide shading in summer and make sure the sunlight gets through in winter. Just need the angle of the sun each month and a protractor to mark it on the plans….
    – Solar Mike
    Commented Jan 10, 2022 at 7:37
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    @SolarMike The exposure can really affect the temp in a house. My subdivision was built in 1980 with large trees all over the place. Hurricane Andrew wiped out most of the trees. The high bill complaints went through the roof (no pun intended) due to all th increased exposure.
    – JACK
    Commented Jan 10, 2022 at 12:53
  • I know, we designed our west window so that on a sunny christmas afternoon we could enjoy the sun streaming through the window and in summer the sun does not touch the glass.
    – Solar Mike
    Commented Jan 10, 2022 at 12:56
  • It could be exposure or it could be due to the OP setting the thermostat lower than their neighbors in the summer. Or more likely a combination of the two...
    – mmathis
    Commented Jan 10, 2022 at 14:33
  • @SolarMike I always wondered if your username was eco related
    – Caius Jard
    Commented Jan 10, 2022 at 16:11
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As heat can travel through your walls and roof in either direction, what you should really take from what the electricity company is telling you is that your house is inefficient all the time except when the ambient temperature outside is close to the desired internal house temperature.

If you improve the insulation to reduce the cooling energy needed then that will also help reduce the heating needed.

However, if you employ shading to reduce the incoming solar radiation in summer then that ne3eds to be removed in winter as that is useful heat addition that is free.

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  • We keep the house around 70-75F. The graph shows our house being efficient even in the months when the average ambient temperature is under 40F, so I don't think the graph is saying our home is inefficient all the time except when ambient temp. is close to home temp.
    – Fijoy Vadakkumpadan
    Commented Jan 9, 2022 at 16:12
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    So convert your gas bills to kWh and plot those values on the graph... You will soon find out.
    – Solar Mike
    Commented Jan 9, 2022 at 16:14
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    Pull out your gas bills for the same time period, and think again.
    – Ecnerwal
    Commented Jan 9, 2022 at 16:14
  • @Ecnerwal not had a gas bill for heating in more than 30 years. Deigned a house which uses sunlight, solar water heating and a small woodstove (only 2m^3 wood per year needed). We used degree days to simulate the house before the build, but the downvote means I will keep the knowledge - it's hard to help sometimes.
    – Solar Mike
    Commented Jan 9, 2022 at 16:23
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    Not my DV, and I was referring to the OPs gas bills. We commented at the same time.
    – Ecnerwal
    Commented Jan 9, 2022 at 16:26
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If your a/c system is 20 years old it is going to be much less efficient than a new a/c. This is due both to the age of the unit as well as the fact that newer units are more efficient to begin with.

It might be time to replace your a/c. I used to have the same issue with my 15 year old unit (much higher usage in the summer compared to similar homes). It died in the middle of the summer and when I replaced the a/c the problem went away (I went with the most efficient a/c model available).

On another note. I highly recommend you replace your a/c before it fails. It will fail at the most inconvenient time and you may have to wait along time to get it replaced. In my case we had to wait 2 weeks and I was forced to get 3 portable ac units just to get by. With pandemic supply chain, who knows how long you would have to wait.

At 20 years, you are past borrowed time on that unit. You should replace both the a/c and central heating at the same time.

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  • While it is true that a newer unit will be more efficient, it's not true that this will make the questioner's utility bill go down a great deal. You will, at best, see marginal gains. The only way to see it drop a lot is to not run the unit (i.e. turn the thermostat up in the summer)
    – Machavity
    Commented Jan 10, 2022 at 14:16
  • @Machavity The bump in the graph appears to be mainly from air conditioning. OP's AC appears to use 150W average, while "average home" uses 100W average. That kind of efficiency improvement from AC maintenance or replacement is entirely plausible.
    – jpa
    Commented Jan 10, 2022 at 15:01
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    Where in the world do you live that you are “forced to get 3 portable AC units just to get by”? Venus?
    – Michael
    Commented Jan 11, 2022 at 8:09
  • @Michael Maybe Washington State? scientificamerican.com/article/…
    – JimmyJames
    Commented Jan 11, 2022 at 15:52
  • @Michael Most portable AC's are single tube so you are creating a negative pressure environment which pulls in heat from the outside. They constantly fight themselves and are much much worse than the through the window versions (though of course a necessary evil) so they are terrible at cooling ... You'd want at least 3 for any average+ sized US house -- there are many places here where it's still going to be near 80 and very humid even in the middle of the night
    – eps
    Commented Jan 11, 2022 at 19:18
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Most likely, the difference is because you have AC, and many of your neighbors don't.

I'm guessing you live in the Bay Area, or somewhere close - that's a PG&E graph, if I don't miss my guess, and those temperatures are nearly identical to those in many places in the Bay Area. Most houses in the Bay Area don't have AC - where I live I can't think of one person I know who does (and the houses in my area are not cheap!). Temps that top out in the low 80s, and the low on those days is likely in the 50s, means that there's just no need for it.

If 1/3 of the folks in your area don't have AC, then - guess what - those numbers make sense.

1/3 * (500) + 2/3 * (2500) = ~1800

So maybe you're a bit inefficient, or maybe you set the AC a degree lower than the others in your area - or the numbers are more like 1/2 and 1/2 (in which case you're better than average).

In an area like the Bay Area (or really, any area with a climate like that describes - temps above freezing and never unbearably hot), there's not a lot you need to do in terms of insulation. Particularly in the summer, look at your differentials: if the house temp is 72, and the high is 84, that's a very small difference - even with terrible insulation you'll mostly not see a big difference. In the winter it's a bit more, maybe a 30 degree difference, so there the insulation matters more.

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To answer one part of question: what can you do to reduce your home's relative inefficiency in summer:

Considering the other good answers

  1. you have A/C, many of the group of compared homes do not
  2. your inside/outside temperature differential in cooling degree days is not very high. You have cool evenings and not terribly hot days.

So:

  1. Improving your insulation won't help much
  2. Using less A/C is the key.

How to use less A/C: Minimize heating from the sun and maximize natural cooling

  1. Close shades and blinds, installing better ones if needed, where the sun shines in strongly
  2. Install through-fans, ideally a strong attic fan (if you have an attic) that sucks air in through open downstairs windows and pushes it out the attic vents. Depending on the arrangement of your home, you generally want to create air flow from lower windows through the house to upper windows.
  3. Use the through-fans to cool the house at night to the coldest temperature you are comfortable with.
  4. Continue using them through the course of the day until the air being sucked in is warmer than the air inside. Then close the windows and blinds and do nothing til the house reaches the highest temperature you are comfortable with.
  5. THEN AND ONLY THEN use your A/C ... but as soon as the sun goes down, switch back to the fans.

I suspect the above will move you closer to average. If you want to get closer to "efficient" you'll just have to go colder at night and warmer in the day.

Then you can take things a step further: Upgrade your A/C. It's 20 years old. Sooner or later it will fail. When it does, install a 2-zone system (upstairs/downstairs) with timers so you only cool where it's needed, or better yet, install mini-splits in the rooms that need them most and install occupancy sensors in those rooms.

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your house is not energy efficient during the winter. it has the same insulation in winter and in summer. your electric consumption goes high during summer because you use electricity for your A/C to cool your house and switch it off during cold months.

to use less electricity during summer: Better heat insulation and more efficient A/C (e.g. DC invertor type)

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