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How to use Economy 7 effectively

This page is applicable only to dwellings whose Economy 7 meters are controlled by an offline timer. If your installation has a Teleswitch or other device that can be remotely controlled by your supplier, then you have no way of knowing the exact times they'll switch in and out of Economy 7 (they have the right to vary it from night to night to even out the grid, and they can even give you one or more peak-rate "gaps" during the off-peak period), which means most of the optimisations on this page won't apply and all you can do is let the supplier look after your storage heaters. But if your meter's timer is not remotely controlled, read on.
Many people have Economy 7 but do not use it effectively. If you do it right, you might be able to put over 70% of your annual use into the cheap period (in which case watch out for meter readers swapping the figures!)
  1. Know what your personal cheap period is. Not all meters are set for 12:00-7:00 GMT. Some are set for 12:30-7:30, and other settings are also possible. It can vary even in the same region with the same supplier. If in doubt, you might be able to ask the supplier. Then, check the meter's clock and note how far out it is (power companies generally don't mind some inaccuracy)---the cheap period for you starts and ends when that clock shows that meter's preset times. Either work out how this translates to 'real' clock time, or find it emperically by listening for the "click" of the relay in the meter cabinet (not so easy when two or more flats share a cabinet), or by monitoring which rate the meter is displaying and/or whether a storage heater draws power when turned on at maximum input---if you can't watch it closely enough to log the exact time of change, you might at least be able to sample it frequently enough to know it within narrow error bars.
    The meter's clock might need further checks every few months in case its drift has changed.
  2. Try to adjust your sleep habits so you have an hour (or two) of cheap time while awake. This might simply be a matter of getting up a little earlier to catch the end of the period. (I do not recommend staying up all night for it.)
  3. Schedule most of your high-energy activities for that time. Start the washing machine (if you have a full load). Vacuum. You might as well charge all batteries and run the printer too. (But don't do anything not needed.) This strategy can make Economy 7 worthwhile even outside the heating season, especially if you are not a heavy user of electric cooking.
    • It might be considerate to wait until just before the end of the period before doing anything noisy. That's why it's useful to know the exact time it will end.
    • I previously included "heat the water tank (if it's needed that day, and use a timer if you only need warm not hot)" in the above list, but be careful---storing water above 20C but below 50--60C can breed Legionella bacteria (this is particularly a concern if the water can get into air droplets via a shower or aerator). It's better to heat only as much water as will be used, and use it soon.
  4. Take more control of storage heaters. If you are awake an hour before the cheap period ends, then you have the option of changing the heater controls at that time. Rather than being limited to the full 7-hour charge, you could have a 1-hour charge or a 6-hour charge, or even change the level for the last hour. Since heat inevitably leaks out at night, it's more efficient to refrain from generating at least most of it until that time, as long as you can still get enough (this depends on the weather, and also on the condition of the heater---it's probably not applicable to a half-broken one that charges very slowly because only a fraction of its charging elements still work, although if you suspect you have one of those because a wireless "energy monitor" is telling you it's taking only a couple of hundred watts, it's more likely you've mis-connected the transmitter in a way that neglects cable 5).
  5. Check if you really need to store any heat at all. If the only heat you need is first thing in the morning, then a lower-wattage non-storage heater during the last part of the cheap period might be enough. (Watch the meter if you're not sure of the wattage.) You may wish to measure the typical consumption of a night's charge on "low", calculate how many hours of on-peak heating you can do for the same cost, and don't store on days you don't need that many hours (the exact thresholds will vary but at least you have a starting point); if some of that non-storage heating will take place in the cheap period anyway then so much the better.
If all else fails, you can switch to a non-Economy 7 tariff without needing a meter change (they'll just add the two readings together), but you might be surprised how low the annual percentage of night usage can go before this is worthwhile (do the equation, or use my energy deals sanity checker).
The above ideas are provided in the hope that they are useful, but they do not constitute medical or financial advice. Always consider the individual circumstances before implementing any energy saving plan.
All material © Silas S. Brown unless otherwise stated.