Programmable Thermostatic Radiator Valves

Just programming up the new valves before installation next week, and thought I’d do the calculations.  The valves shown on the right aren’t the same, but the price is about the same, and the calculations still apply.

I managed to get two valves with bodies for £53.44, and our gas prices at the moment are £0.03182/kWh, so I need to make savings of 1700 kWh to reach break even point.

The plan is to put them in the lounge on the radiators there, which are 600mmx1400mm (1500 W), and 600mm x 1000mm (1000 W).

Currently the radiators have no thermostat whatsoever, and our heating is on from 6:00 until 8:00 every morning and from 15:00 until 22:00 every evening for the 180 heating days of the year.

That equates to (1.5+ 1.0 kW) * (2 + 7 hours) * 180 or 4050 kWh/year to heat that single room, but our total usage doesn’t seem to be anything near that high when scaled up.

Last year our annual usage was 15200 kWh of gas, of which we averaged 15 kWh/ day for heating water and cooking (or 5500 kWh/year), leaving 9700 for heating.

I’d guess that based on the sizes of the other radiators in the house that the heat used in the lounge is about 1/5 of the total, or 1940 kWh a year.

I propose to limit heating in that room to be only between the hours of 17:00 and 21:30, representing a reduction of 50% on the amount of time heated, generating a maximum savings of  970 kWh/year.

Being very pessimistic (by assuming we get only half that savings), it looks like the devices should pay back in under 4 years.

For comparison, last year our gas consumption in the heating season was 60.73 kWh/degree day. Our target this year for kWh of gas per degree day is now: 55.55 representing a 9.5% reduction in consumption if we are to achieve payback in two years.