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I have 3 appliances that use natural gas: Water heater, gas furnace and gas stove. How can I tell how much gas each is using so that when I make energy efficient improvements I have a way to tell how much efficiency of improvement I have made.

For example I am planning to shift to an electric heat pump with a gas furnace as a backup. Ideally my gas furnace usage should drastically reduce, but I can't tell the difference just by looking at the gas utility bill.

Is there an individual gas meter that can be installed by myself?

Thanks!!

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  • Are you in a temperate climate? Climate Zone 4 here. People tried to tell me I'd want a gas furnace as a backup for my heat pump, but I went with strips for a backup as I'm trying to decarbon. Practical experience has shown it runs the strips at worst 10 hours a month and it costs about $1/hour to run them, meaning putting in a gas furnace made no sense at all alongside a heat pump. Cost has been slightly lower overall with better comfort.
    – KMJ
    Nov 21, 2023 at 19:47
  • It is trivially easy to measure electricity yourself because in addition to an inline meter for the whole house (what your utility uses) you can use a clamp meter on anything from your entire service (provided your panel has accessible wires from the service feed) to individual circuits. With gas there is no simple equivalent to a utility-style meter. Nov 21, 2023 at 20:15
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    Why can't tell by the gas utility bill? You should see a change from "last year's" usage or what not?
    – rogerdpack
    Nov 22, 2023 at 15:49

3 Answers 3

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Stove usage will be peanuts. We had neighbours who had standard gas range (4 burners and oven) that they ran off a pair of 100 lb propane tanks. They would go weeks to months between tank trips.

Electric stoves are responsible for only about 2.8% of the typical house's electric bill.

Here, I would determine the difference by looking at my gas bills for cold months vs warm months. In the summer we go months without heating. This gives me a baseline for what the gas water heater would use. Assuming roughly equal amounts of hot water usage summer and winter, the winter gas bill - summer gas bill = winter heating use.

Right now here gas is a lot cheaper. Natural gas is about 2.25 /GJ (wholesale) to 5.50 fixed term 5 years. (or aobut 25 cents a therm for the 2.25 /GJ) Electricity is variable, but I'm currently at 8.2 c/kWh,but I pay for wire services separately. My gas coop can only charge $1/GJ over market price.

A GJ = 277 kWh

So a GJ of electricity is roughly $22.16

Heat pumps can be more efficient. But once it gets cold outside, it has to work a lot harder. House heating with a heat pump is the better investment -- you get higher COP with smaller temperature differences. For DHW you are heating water 10-15 C hotter.

This also means that you can't use the same system to do both, without losing a lot of efficiency.

Ideally in a heat pump system you want to heat a lot of water a little bit. So where my baseboard hot water heaters use water at 60 C, while an under floor system will typically run 30 degrees cooler.

I'm reading real life numbers in zone 4 climates of overall yearly efficiencies of 2.5 to 3.5

Add to this: You have a more complex system.

If I was going to throw money at this, I would put grid connected PV on my garage roof, and sell power to the electrical company in summer and buy it back in winter. Continue to heat mostly with wood, and continue to pay my 40-6o dollar gas bill each month.

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    Just to confirm Sherwood's point about a gas stove, we use propane and the only gas appliance in the house is a cooktop. We temporarily connected a 20 lb tank (standard barbecue size) when we moved in, and found that it lasts for 4 to 6 months. Gas consumption for cooking is truly negligible, and can be ignored.
    – Mark
    Nov 22, 2023 at 6:27
  • To add about the gas stove consumption. I just refilled my propane tank, which is only used for kitchen stove. $276 to fill up. 5 years since the last fill up, so less than $5/mo.
    – Cheery
    Nov 22, 2023 at 17:12
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Assuming you live in the house year-round and have well-defined seasons (e.g., at least 3 months where it would be very rare to use the furnace) then you can figure it out a rough approximation from your gas bills.

Usage (usage or cost) in average of summer months is the baseline. Multiply that by 12 to get your (water heater + cooking) usage.

Add up 12 months of usage (doesn't matter if it is January to December or July to June, whatever is easiest to find, but should be 12 consecutive months). That is your total usage. Subtract the (water heater + cooking) usage and that is your nominal furnace usage.

It is often easiest to do this based on cost. However, some utilities price natural gas higher during the winter (generally, based on higher demand) and there are also variations due to overall energy pricing (that includes oil, natural gas, electricity - everything relates in a number of both market-driven and regulatory ways). So a somewhat better way to look at it is based on usage (typically Therms or MMBTU or CCF in the US), though to figure out cost-effectiveness you then have to find the rate schedule and then you really end up back at the cost anyway.

The good thing about looking at usage rather than cost is it tells you not just the overall cost, which can be very roughly compared to alternatives based on degree-days, size of your house and other factors, but it actually gives you a real usage to compare. If you use 'x' Therms and currently have an 80% efficient furnace, you know how much heat is being generated and put into your house, so you can then figure out what it would cost for various alternatives because you don't have to guess about how good your insulation is, how leaky your windows are, etc. - that is all factored in to your actual usage already.

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If your residence has a gas meter you can access, you can watch the usage of each device while all the other devices are off. Pilot lights can probably be disregarded, no need to put them out.

The meter dials/numbers will advance faster the more gas gets used. Inspect the meter and web-search it to determine how it reads gas usage and the units it measures. Then time the meter with a stopwatch as it advances from one number to the next while the appliance is running all by itself. You can average the time over several turns of the meter to compensate for low/high changes in the appliance operation if you want.

The actual time it takes to advance from one number to the next can be divided to determine the amount of gas used per unit time for the appliance. (I used a stopwatch and inspected the meter dials to determine how much my gas furnace's new gas valve was letting into the furnace: the valve had to be tuned to let only a certain amount of gas in, so the furnace thermal rating would not go too high. The furnace was rated in BTU's, and I converted to determine how many cubic feet represented that number of BTUs, then watched and timed the meter to make sure that number of cubic feet went into the furnace.)

You can convert the gas usage per unit time to therms, BTUs, kilowatt-hours, etc, to compare electric vs gas appliances for a particular application.

A web-search reveals that there apparently are gas submeters that can be used on individual appliances. However, the local code authority (AHJ) will have something to say about if and how they are used, and you'll probably not need such a submeter for the long term. Timing the main meter can give you the same data with the equipment you have now.

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