Is my calculation correct?

greatcapp

If I have a Ideal HS15 boiler that is a 15kw unit, and I'm currently paying just under 4p per unit of gas, then to run my Central Heating for an hour would cost 4 x 15 = 60p?

And likewise, if I have a portable air con unit (that can also heat), which is 1100 watts and I pay just under 20p per kwh for my electric, then that is 1.1 x 20 = 22p?

So, in theory, using the air con (electric heating) would be cheaper than turning the central heating on, but obviously, only heating 1 room in the house (good enough in a working from home situation during the day)?

The_Fat_Controller

Boiler ratings are normally for the full flow rate when heating water to taps/bath/shower with the boiler running constantly.

When using CH the boiler will cycle on and off, even when heating the house from cold, so the usage over an hour will vary on how much work the boiler has to do to reach and maintain the set temperature, lots of variables there.

Astria

Also, don't get unit of gas and kWh of gas mixed up. 1 unit of gas = 1.0 × 1.02264 (Volume Correction) × 39.2 (Calorific Value) ÷ 3.6 (convert from joules) = 11.1 kWh.

Best way to measure consumption is to calculate a background reading (excluding the device), then another reading including the device, and then subtract one from the other.

markin

It would be hr 2,3,4 where the boiler only has to fire up for 15min to top up the heat where it will match or beat the electric cost, but then the electric heating cycle would also be shorter, You would have to just measure the total daily gas usage and the electric usage with a plug in device.

And turn the boiler flow temp down, Target 50c, It takes longer to warm up but more efficient when condensing.  As its a heat only the hot water tank may need to be set lower 50c

Dial Min 30c - max 80c
Min output 8.8kw  - max 14.6kw

Reed_Richards

If your aircon uses an air-to-air heat pump (and many modern ones do) then you might get 3 to 5 kW of heat for every kW of electricity used.

QrizB

Reed_Richards said:

If your aircon uses an air-to-air heat pump (and many modern ones do) then you might get 3 to 5 kW of heat for every kW of electricity used.

It's a portable, so that's going to be more like 2.5-to-3. It should be shown on the ErP label and/or data plate.

markin

I've seen many portable air con units that seem to just use an element for heat, I think only the 2 hose versions have had reverse heat pumps, from memory.