Gas Vrs Electric combi boilers :which is cheaper to run ??

guymitchell · 5 September 2011 at 2:06PM

I'm about to have 2.8Kw solar panel system on my house so the cost of running an electric boiler may be reduced. Although saying that electric boilers start at 9kw so would still need to find the other 6.2 just to run the smallest boilers on the market...and that's only assuming it is run during the day.

So gas it is then.

Cardew · 5 September 2011 at 2:20PM

guymitchell wrote: »

I'm about to have 2.8Kw solar panel system on my house so the cost of running an electric boiler may be reduced. Although saying that electric boilers start at 9kw so would still need to find the other 6.2 just to run the smallest boilers on the market...and that's only assuming it is run during the day.

So gas it is then.

If you have a 2.8kWp PV system, it might never generate 2.8kW* - depending where you live in UK. Even if it does generate that amount it will be around midday in high summer on a cloudless day.

Much of the time it will be producing way below 2.8kW.

*The rated output of any PV panel is achieved under laboratory conditions of 'sunlight', temperature etc. Thus a, say, 225wp panel will never reach 225 watt output in Northern Scotland, but could exceed that in Cornwall.

donjlsolaracc · 11 October 2011 at 4:30PM

I am seriously considering buying solar panels about 3.5 Kw would it be a good idea to use the daily input to run an electric combi boiler rather than existing gas boiler Just noticed reply from Cardew 05/09/11 It has answered by question

macman · 11 October 2011 at 5:22PM

Pretty pointless, since most of your heating /hot water demand on the combi will be during the colder hours of darkness, when the solar PV will output zero.
When it's outputting the maximum (summer daytimes), you will have no heating demand.

donjlsolaracc · 12 October 2011 at 9:55AM

would it be feasable / economic to have a parallel hot water only syatem fitted via valves, with a hot water tank that could be heated via an emersion heater during the day when PV power is available

macman · 12 October 2011 at 10:01AM

Then why not heat the hot water directly using solar hot water panels?

sparky_55 · 29 October 2011 at 4:30PM

This all depends on whether or not you want to invest in solar as well. If you invest in solar you can produce electric which can be used in different ways

1) electric central heating only boiler to background heat your home for free during the day using free energy produced on your roof and then electric heating boiler works less at night because it's not lifting the ambient tempuratute by 10+ degrees which is what costs the money.

2) electric central heating only boiler to background heat your home for free during the day using free energy produced on your roof and then switch back to gas at night. I've seen a few dual fuel central heating systems like this and they work very well...free electric during the day and reduced gas costs at night

3) Never have a combi...it costs far less to gently heat water and raise the temperature of radiators than it does on demand. Hot water on demand costs a fortune compared to gentley heating a tank of water and if you have PV you can change the electric immersion from a 3kw to a 1.5kw and put it on a timer to come on for an hour during the day to give yourself a free tank of hot water via your PV system

4) Another option is storage heaters powered during the day by your PV so you have free heat at night.

Even at 21p per KW on the new feed-in-tariff rates, if you're getting free electric and using ALL OF IT (which is very important), then you are getting free electric for 25 years and the value of this saving increases every year as electric prices go up while you're getting it for free.

If you're a pensioner for example...one things for sure...your pension will not match the increases in forthcoming gas and electric costs so the best way to protect yourself from increasing costs is to make it yourself on your roof and use all of it to heat your house therefore reducing or eliminating your gas while utilising free electric.

sparky_55 · 29 October 2011 at 4:44PM

you can also buy electric boilers that you can control the power used. You can for example reduce from 14kw to 7 kw so draw from the grid is minimised. electric boilers are far much more efficient than any gas boilers...even the new gas condensing boilers because they only run at 90% efficiency when condensing whereas electric boilers run at 99.8 all the time. Condensing boilers take a while to get into condensing mode so don't be fooled by the stats flying around. The real measure of any central heating system is how many minutes an hour it's using energy once the radiators are at temperature. This of course depends on the heat loss value of the house but you'll be surprised at the performance and costs of running electric boilers once the rads are at the desired temperature. For the avoidance of doubt there's no disputing electric prices are 2.5 times higher than gas but when the electric is free from PV then you're into a much differant argument

chris1973 · 29 October 2011 at 7:51PM

electric boilers are far much more efficient than any gas boilers

This is true, but the void is narrowing, and now the best and latest gas boilers may only be 9% - 10% less efficient than 100% Efficient Electric Heating. Still more than enough to maintain the price difference between 3.8p per KW/H on Gas and the 12p (or 8p on E10 Tariff) of a KW/H of Electricity.

Yes, you can get E7 tariff's which offer rates of 5p - 6p per KW/H but these are limited to 7 hours per night, and its highly unlikely that even the best boiler would store enough hot water heated only between 1AM and 8AM to supply an average family sized property with enough hot water and central heating output to heat the house in the middle of winter for the 17 hours which elapse between heating cycles to the boiler!. So some daytime electricity input would be required, and on any subsidised tariff like E7, the daytime rates are sold at premium prices well over the odds, I pay 19p per KW/H for daytime Electricity from Npower on an E7 tariff, if I needed to run an Electric boiler now to top up the water temperature for my Central Heating, an average sized boiler rated at 14KW, would be consuming 14 Units per hour at 19p = £2.66 an hour to top up the heat outside of E7 - hardly 'cheap'

@ OP - Have a search of the forum, i'm sure you'll find a lot of the 'Why are my Electricity Bills so high' come from people with Electric Boilers. Seriously, from somebody who currently lives in an All Electric property, I envy your GCH!

Divads · 31 October 2011 at 12:33PM

I have Gas Central heating modern gas condensing boiler. An open vented system with 2 tanks both indirect with emersion heaters. I use economy seven to heat these at night for hot water during day each tank being used separately. Topping up one tank with gas if nescessary. I have just had installed a Solar PV system and am looking for a way of using its spare electricity to top up the domestic hot water tanks.

Does any one know of systems able to do this? Both emersions are 3kw.

Divad

Gas Vrs Electric combi boilers :which is cheaper to run ??

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