Saturday, 28 September 2019

The surprising cost of a pilot light (waakvlam)

We have a low energy bill. This is the case because we've done quite a lot of work in our home to improve the insulation so that our central heating rarely comes on, and we've tackled our electricity consumption by installing solar panels. However, we've not yet done anything to the gas equipment in our home which was already here when we moved in 12 years ago, in part because until now it's not been easy to tell which piece of equipment used most gas so should be targeted first.

While we've had a smart electricity meter for almost a year now, and I've used a plug in measuring device for much longer to check which appliances had higher than expected consumption, our energy company didn't install a smart gas meter until a week ago. The old meter was not easy to read for small levels of usage. But the new meter has made it easy to find out something which I had long wondered about: How much of our not very high gas consumption was wasted to no effect.
The new gas meter. Since installation we've burnt 5.725 cubic metres of gas.
The gas water heater
How much gas does a pilot light (waakvlam) use ?
Our house has three devices which run on gas: The gas hob in the kitchen, the central heating boiler and a separate water heater which heats water only for the shower, bath and bathroom sink.

The water heater is really old. Old enough to use a pilot light (waakvlam) instead of starting itself with an electronic igniter whenever hot water is required.

If you're unfamiliar with what that means, there is a very small flame which burns continuously, 24 hours a day, 365 days a year, just waiting for someone to turn on the hot tap so that it can be used to ignite a much larger flame to heat water.

In the past I've asked several people who work for the gas company, or otherwise seem to know about gas appliances how much gas is used by such a flame and I've always been re-assured that it's "next to nothing", "unmeasurable" or "similar to a mobile phone charger", but I was never quite convinced. The new gas meter has allowed me to measure how much gas is being consumed and the result is surprising.

The pilot light. It's small, but any gas burnt here is wasted.
Meten is Weten. It costs how much ?
One day this week we took readings from the gas meter while avoiding using any gas appliance for 18 and a half hours so that period passed with only the pilot light burning gas. Over 18.5 hours, the meter showed that 0.283 cubic metres had been consumed. That equates to 0.366 cubic metres per day or 134 cubic metres per year.

134 cubic metres of gas isn't insignificant at all ! In fact, it turns out that in summer months our gas usage is dominated by the consumption of the pilot light, which consumes more than we use for hot water and cooking combined. Over the whole year it consumes rather more gas than we use in February to heat our home. It's an appalling waste not only of gas but also of money: That pilot light costs us nearly €90 a year to run.

Like a phone charger ?
The comparison made previously with a mobile phone charger is particularly absurd as phone chargers genuinely do consume an unmeasurably small amount of electricity when they're not in use (unplugging them is something that some people do in an obsessional way because it looks like it'll save energy, when actually the effect is almost nothing at all). But this pilot light consumes a very measurable amount of gas. 134 cubic metres of gas is equivalent to about 1340 kWh of electricity. If a phone charger used that much it would certainly be measurable. It would also add somewhat more than €100 a year to the electricity bill and the charger would be rather hot rather than cold to the touch.

The next step
Obviously this old water heater has to go. That has long been the plan because actually we'd like to get rid of gas altogether. It's not happened yet because we prioritized insulation and electricity first. But discovering how much this thing wastes has given new urgency to the plan. At the very least we need to be rid of this water heater. It appears to be possible to buy an instant electric heater for about the annual cost of the gas for this, and an electric heater would effectively cost nothing to use because it would operate on the excess electricity from our solar panels which we currently export to the grid and for which the electricity company pays us very little. So I expect to change this quite soon.

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