Are my calculations re costs of heating correct?

PhotoMan

Summer is over and it's time to use some heating to warm the lounge in the morning. We have an electric fan heater and a gas fire. I want to compare the costs of using them.

Rates cut and pasted from the contract rate on my energy supplier's web site.

Electricity supply 

Unit rate

26.51p per kWh

Standing charge
56.02p per day

Gas supply
Unit rate
6.83p per kWh
Standing charge
29.62p per day

Gas fire - gas consumption (cut and pasted from the manual - Valor Black Beauty)
Has a maximum natural gas input of 5.1kW (Gross)
Has a minimum natural gas input of 1.55kW (Gross)

Electric fan heater - 2,200 Watts.

So by my calculations the cost of running the fan heater will be 26.51p x 2.2kW = 58.3p per hour, ie about 1p/minute.
And the cost of running the gas fire on its highest setting will be 6.83p x 5.1kW = 34.8p per hour ie about ½p per minute.
And running the gas fire on its lowest setting will cost 6.83p x 1.55kW = 10.6p per hour ie about 0.18p per minute.

Have I made any incorrect assumptions here or are my calculations valid and correct? I just want to compare the cost of running the fan heater with the cost of running the gas fire.

debitcardmayhem

Probably better in the energy forum https://forums.moneysavingexpert.com/categories/energy

Ayr_Rage

With the electric heater you will benefit from all the energy less the cost of the fan (minimal)

Some of the energy from burning the gas will go outside via the flue, so you will need to find out the efficiency of the unit to make your calculation.

https://www.direct-fireplaces.com/resources/gas-fire-efficiency/

PhotoMan

Ayr_Rage said:

With the electric heater you will benefit from all the energy less the cost of the fan (minimal)

Some of the energy from burning the gas will go outside via the flue, so you will need to find out the efficiency of the unit to make your calculation.

Thank you.
The efficiency of the gas fire is given as 81%, with maximum natural gas output of 4.0kW and minimum natural gas output of 1.0kW. But I'm not concerned with the output so much, I just want an idea of cost per minute (or hour) to run.

PhotoMan

debitcardmayhem said:

Probably better in the energy forum https://forums.moneysavingexpert.com/categories/energy

Can mods move the thread or should I repost in the above forum?

GrumpyDil

Best way is to report your post and ask for it to be moved. 

PhotoMan

GrumpyDil said:

Best way is to report your post and ask for it to be moved. 

Will do. Thank you.

Ayr_Rage

To run the gas fire at an output to match the electric fire output (2.2 kW) requires 2.716 kW of gas (2.2 divided by 0.81)

Therefore one hour of the gas fire costs 2.716 x 6.83 = 18.55p

One hour of the electric heater costs 58.3p as per your original calculation.

That makes the electric heater 3.142 times more expensive to run than the gas fire assuming the 81% declared efficiency.

Your original calculations are correct, but remember on full output the gas fire will using 5.1 kW to give you 4.131 kW into the room.

Heedtheadvice

Plus the cist to run depends upon not just the continuous input power cost but the efficiency (as above) and the required output power to meet the temperature needs. 

Is your gas fire output a manual control ( such as high, medium, low) or is temperature controlled via a thermocouple and thus automatic if the former then likely poor control with under/over heating and maybe a tendancy to overheat. Conversely radiant heat output makes one feel warmer so possible use less!

A fan heater usually has a bimetallic strip control to attempt to keep the set temperature constant. Not the best control but should limit too much overheating. Convected heat blown in one direction not always as comfortable as radiant heat.

So to compare cost is not easy and depends on your personal choice and how you control it too. One really cannot do a simple comparison but it is a starting guide!

facade

As above, the gas fire is much cheaper to run.

You could replace the electric heater with a small heat pump AC unit like the Mitsubishi-SRK35ZSP, this is rated at 930W in for about 4KW out so for equivalent warmth to the fan heater it would cost 24.65p an hour. (And it would cost £1000 ish installed, plus an annual or biannual service....)

I am seriously considering getting one for the Summer though

cerebus

facade said:

As above, the gas fire is much cheaper to run.

You could replace the electric heater with a small heat pump AC unit like the Mitsubishi-SRK35ZSP, this is rated at 930W in for about 4KW out so for equivalent warmth to the fan heater it would cost 24.65p an hour. (And it would cost £1000 ish installed, plus an annual or biannual service....)

I am seriously considering getting one for the Summer though

Thats not possible if you put 930watts in you put 930 watts out,  you cannot make watts out of nothing.

Heat pumps are only any good too if you have a home that is extremely well insulated , poorly insulated houses will never get warm using a heat pump alone