Electric Boiler Output Temperature

echo82

Hi all,

We have a complicated heating system - a separate 9kW and 6kW boiler for different parts of the house, each with a Nest thermostat and separate hot water provided with an immersion heater (largely used overnight with Economy 7).

The advice for turning down the output for Combi boilers to make them more efficient presumably doesn't apply to an electric boiler. The output on ours is adjustable between 65 and 80C, and is set to the lower end. Presumably turning it up costs more to heat, but means the rooms heat quicker (it is very slow to heat). There must therefore be a 'sweet spot' where it is optimal, but how do you know where it is? Is it just trial and error, or just heat everything as quickly as possible?

Thanks!

Astria

The only way of really knowing is by trial and error - try it at the low end, measure the consumption, and then increase, set it to a temperature where you are comfortable.

One thing I will say though, as radiators retain heat, a higher output temperature can over shoot thermostats and TRVs, which then means the heating is off for longer periods, so you might feel "cool" quicker in some rooms, so in this case a lower flow temperature will give a more even temperature and thus more comfortable, but the boiler will switch on more. Both should be very similar in cost though.

Is there a reason you can't invest in something more like a heat pump solution?

There are also other electric solutions such as heating a mass inside a boiler to high temperatures during E7 time, and then using that to heat the water during the day, a bit like storage radiators.

Reed_Richards

If all your pipes are within the insulated fabric of the building then it doesn't really matter what water temperature you use, from the fuel economy point of view.  In my house some of the heating pipes run above the loft insulation so any heat lost from those pipes is wasted.  So for me it makes sense not to have these pipes any hotter than necessary because the hotter they are the more heat they will lose.

macman

If it's unacceptably slow to heat, then just nudge it up by 1 or 2C each time, until you find an acceptable compromise.
Your electric boiler doesn't condense, since it has no flue gases to waste heat, so the flow temp advice for a condensing combi is not relevant.

echo82

Thanks all - trial and error it is for now!

Ectophile

The good news is that nothing you do will make it more efficient.  Electric heating is always 100% efficient.

The bad news is that nothing you do will make it more efficient.  I reckon that you're probably paying about £4 an hour with both boilers on, at least while they are heating up from cold.  Less once they are up to temperature.  It really is an extroardinarily expensive way to heat a house.

On the other hand, heat pumps are around 300 to 400% efficient.

Gerry1

Is it absolutely impossible to get mains gas in your area?  Nothing is more expensive to run than an electric boiler.

macman

Gerry1 said:

Is it absolutely impossible to get mains gas in your area?  Nothing is more expensive to run than an electric boiler.

Even more so since you are running the heating side on peak rate E7! Surely it would be cheaper to switch to a single rate tariff and sacrifice the cheap rate E7 hot water?
Who on earth dreamed up that system?
I'd rip out the boilers and install modern NSH's (Quantum's) to work with the existing E7. Expensive, but it won't take long to recover the capital cost at current prices.

echo82

Gerry1 said:

Is it absolutely impossible to get mains gas in your area?  Nothing is more expensive to run than an electric boiler.

Afraid not - entire area is not on mains gas.

macman said:

Gerry1 said:

Is it absolutely impossible to get mains gas in your area?  Nothing is more expensive to run than an electric boiler.

Even more so since you are running the heating side on peak rate E7! Surely it would be cheaper to switch to a single rate tariff and sacrifice the cheap rate E7 hot water?
Who on earth dreamed up that system?
I'd rip out the boilers and install modern NSH's (Quantum's) to work with the existing E7. Expensive, but it won't take long to recover the capital cost at current prices.

It's not that bad, as the entire morning heating run can be done on off-peak rate (ends about 0730). If it's cold, we top up the main room we use most often in the afternoon/evening with a log burner which keeps it warm, meaning there is only a small amount of heating in the evening.

I think a heat pump is definitely the way to go, but there's no point at the moment as the insulation, windows etc. are so terrible we're in the middle of sorting those out first. It's also a perfect site for solar, but that's a whole different fight with the council .....