Boiler or emersion in the summer months

collectors

Hi, i am not sure if anyone has done any calculations. But is it better to heat my hot water with my LPG boiler or just use the immersion heater. I have a modern LPG boiler heating a 125LT tank that is very well insulated & it has a 36" top fitting immersion.
The boiler is only around 6 feet from the tank on a fully pumped system. There is 4 adults living here.
Has anyone worked out any pro's & cons.

Cheers

matelodave

LPG gives around 13.6kwh per litre so you need to divide how much you pay per litre by 13.6 to get a price per kwh. You can then compare that with the price you pay for leccy.

Your LPG boiler will only be a round 90% efficient plus you have other losses through the pipework and the fact that the boiler is cycling whilst it's heating the tank so assume that you only get around 80% efficiency from your LPG boiler.

You can then work out roughly how much LPG cost per kwh and compare it with the electricity cost - leccy is 100% efficient because the heater is actually in the water.

I dont know how much you pay for either your leccy or LPG so you have to do the sums yourself.

I pay around 13p a kwh for leccy, which is equivalent to around £1.77 a litre for LPG (13p*13.6 = £1.77)

Cardew

matelodave wrote: »

LPG gives around 13.6kwh per litre so you need to divide how much you pay per litre by 13.6 to get a price per kwh. You can then compare that with the price you pay for leccy.

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I think that is incorrect.

LPG gives around 7kWh per litre.(6.9kWh in the link below.) I believe you are using the kWh content of a Kg of LPG

http://www.elgas.com.au/blog/389-lpg-conversions-kg-litres-mj-kwh-and-m3

That aside, the principle in your post applies.

matelodave

Sorry - Cardew is correct.

I seem to have got kwh/kg & kwh/litre mixed up. I tend to buy caravan sized cylinders of LPG which are sold in kg, whereas bulk LPG gets sold in litres

My LPG equivalent would be 13p*6.9 = 90p a litre