Cheapest domestic hot water (Gas or Economy 7 electric)

hlg_2

I have just discovered that I have an electric immersion heater in my hot water tank. As I am on an Economy 7 electricity tarrif this means I can heat the entire tank overnight for pennies, which is great. Unfortunately though, I use most of my hot water in the evenings, by which time the tank has gone lukewarm.

What is the cheapest way to ensure that I have hot water in the evening? Should I fire up the immersion for an hour before getting home for work (but on expensive rate electric) or use the gas boiler?

Is it cheaper to keep the gas boiler running permanently while the immersion is off (so as to keep the tank at a level temperature, since it is thermostatically controlled), or to give the tank a one off blast in the evening and heat the water back up from lukewarm?

Thanks in advance!

mute_posting

First, is the tank adequately insulated?
A properly insulated tank will only loose a couple of degree's in temperature over say 18 hours if none is drawn off, whereas a poorly insulated tank will leak heat all day.

At the end of the day, I think it boils down to what you pay per kwh for your E7 and what you pay per kwh for gas MULTIPLIED by your boiler efficiency

i.e 4p / kwh on an 80% efficient boiler actually costs 5p (4/0.8) for each kwh of useful output.

HTH

MP

hlg_2

thanks MP.

My plumber checked the tank not long ago and didn't say anything about it being badly insulated, also there doesn't seem to be much heat lost into the linen i store in airing cupboard. I wonder if i'm actually not heating the tank fully, which would explain why it is losing heat so quickly?

mute_posting

7 hours of available (it generally won't take 7 hours and will be turned off by the thermostat when it reaches temp) off-peak over night should be more than enough to heat a full tank (unless it is of industrial proportions lol)

It may be worth checking the thermostat to confirm that it isn't set too low. I belive the reccomended temperature for the stat is about 65 dec c

If you have a thermometor, check the water temp at the closest hot tap at about 8am

Cardew

You need to know 3 things to answer your question. - The price you pay for gas, the price for electricity and the efficiency of your boiler.

In general terms it will be cheaper to use gas than on E7 rates, unless you have a really ancient inefficient boiler(and there will be little in it even then)

It will always be cheaper to use gas than daytime electricity.

If you have gas, a more fundemental question is should you have Economy 7 at all(you do appreciate you pay extra for all the daytime use in the other 17 hours?)

You need to do some arithmetic to see if it will be better to have a 'normal' tariff. For those with gas it normally(not always) pays to not use Economy 7.

Garz

I would agree with the poor insulation. As mentioned, a decent lagged system should not have luke warm water.

hlg_2

thanks guys.

i actually never realised that you could swap between economy 7 and normal domestic tarrifs, nor that I was paying more than i should for daytime electricity! I only use about 20% nighttime electricity so i'll be looking into changing my tariff shortly (as well as checking my insulation!!)

mute_posting

hlg wrote: »

I only use about 20% nighttime electricity so i'll be looking into changing my tariff shortly

You can work out from your unit rates what the break-even point is /would be on proposed tarrif for E7 vs std

you need to know E7, day (inc tier1 & tier2 OR standing charge) for the E7 tarrif And the rates for the corresponding non-E7 tarrif

If you say what supply region and supplier you are someone may help work it out for you.

MP

hlg_2

I'm with ebico, so there is no standing charge, or tiers within the daytime/nighttime rates. I think its about 3.55p for night time and just under 14p for daytime, compared with a 10.5p per unit standard rate.

mute_posting

Well at those rates, the break-even is 33-34%

So I reckon the rates have been set at a 1/3 off-peak break even point

If you definitely are only using / can use 20% off-peak it will pay you to switch (assuming you use 3000 units per year, you are paying roughly £40 per year more than on a standard tarrif)

HTH

MP

Cardew

hlg wrote: »

I'm with ebico, so there is no standing charge, or tiers within the daytime/nighttime rates. I think its about 3.55p for night time and just under 14p for daytime, compared with a 10.5p per unit standard rate.

I think your prices are out of date:

Ebico prices across the regions for E7 range from 3.95p to 5.72p.

We need to know your area to work out 'break even point'

see
http://www.ebico.co.uk/html/e_region.php