I’ve got a 3 bed new build house that’s five years old. It’s an ex rented property and as such the previous owner had stupid pay as you go meters installed, which are a total PITA, BUT, they do allow you to see how much juice you use.

Through the winter months it’s been using around about £130 a month in gas and that’s keeping the house around about 18 degrees and using a clever stat it has temperature changes at certain times to warm the house a little more.

Now the temperature has changed the gas is being used less. So I’m thinking about fitting a immersion timer to the Vented tank and using electric to heat the hot water. It only needs to be on an hour a day, so this begs the question, would it be cheaper to have the immersion on for an hour or the boiler heating up hot water and then pumping it around the tank??

Turn the rads off and put a timer on the boiler?
3.5p-odd/kWh vs 11p-odd/kWh.

Through the winter months it’s been using around about £130 a month in gas

That’s outrageous.

Re the water – why can’t you have the hot water on without the radiators?

Pay as you go meters cost more thna a normal meter – replace the meters and use gas and/or get rid of the tank tbh

Gas is cheaper than leccy re energy costs. Not sure about the efficiency of using a boiler just for HW (which is what we do in the summer). I have an immersion element, but it’s just a back up in case the boiler dies and it takes a day or two to source parts.

it depends on your set up of course but you should be able to heat the hot water without the central heating. Do this as an electric immersion heater will be expensive (think of it as a big expensive to run kettle that you use as a last resort)

We have an open vented CH system with tank. I put in two solenoid valves so the HW tank and Rads can be separately controlled. I suspect the HW efficiency is low as we live in a very hard water area and the HW cylinder is 20 years old, so probably the heating coil is caked in limescale now.

That’s what I do during the summer, turn the oil fuelled C/h off and use the electric immersion for an hour a day. It’s hard to work out the cost of the oil, but the electric doesn’t go up much in the summer, so I think it’s cheaper (but this is instead of expansive oil, gas may be different.)

11″ 3kW immersion heater will cost ~£0.33/day (3 kWh) if on for 1hr/day. I haven’t used a usage factor, it will be dependent on the amount and temperature of the water in the tank at the beginning of the on period. If the immersion heater reaches set-point before the hour, then consumption will be less. You want to be hitting 60degC for a hour/day as per L8 guidance.
May well be worth insulating the living daylights out of it.

insulate io use the boiler to heat the water..should take 20/40 mins max to heat a decent sized tank from cold.. gas boilers do not like long periods of inactivity.. use it and you miss out the chance for a lot of gremlins

surely a modern house wouldnt have a hot water tank?

combi boiler with hot water on demand?

Lots of houses still have tanks. Mains pressure tanks get around combi boilers that can’t keep up with the flow demands of a house with a family where hot water might be needed in more than one place at a time.

insulate io use the boiler to heat the water..should take 20/40 mins max to heat a decent sized tank from cold.. gas boilers do not like long periods of inactivity.. use it and you miss out the chance for a lot of gremlins

Yep, I figure using it for 30mins/day to heat the water is good for it and means I can keep an eye on it!

My house has a hot water tank. It keeps the water hot for days, it’s ace.

Gas is cheaper than leccy re energy costs.

Yep – it’s one third of the cost! Against that gas is less efficient – particularly for heating water, but I would still expect it to be significantly cheaper than using an immersion heater.

It doesn’t really matter how long you will have the emersion heater on for each day.

The simple fact is, to heat the same amount of water, to the same temperature, gas will be significantly cheaper.

If you have a gas boiler then use it.

emersion heaters are for when the boiler breaks down.

I suspect the HW efficiency is low as we live in a very hard water area and the HW cylinder is 20 years old, so probably the heating coil is caked in limescale now.

Where do you think the energy which isn’t being used to heat the water is going?

Electricity is 100% efficient at heating water.

Gas isn’t. You lose heat up the chimney and the less efficient your heat exchanger is (either from the combustion chamber to the heating coil water or from the heating coil water to the tap water) the more heat escapes up the chimney as let heat will be extracted. There is also losses along the pipes from the boiler to the tank and from the boiler casing.

A modern boiler should be very efficient. An old boiler won’t be, through outdated design and degradation. But you still have to go a long way to offset the huge price difference per kW of gas to electricity.

Both types then lose heat through the walls of the tank. And I guess there is the outside bit of the immersion heater that gets hot that is an additional loss on the electric system.

Where do you think the energy which isn’t being used to heat the water is going?

Back out to the pipes so heating your skirting boards or just going back the boiler.. where it reduces the efficiency doesn’t it? Not sure how condensing boilers work.

Where do you think the energy which isn’t being used to heat the water is going?

Lost from the boiler flue by having it sit there short cylcing for 40 mins rather than running at full on for 20 mins, as it can’t transfer the heat very quickly to the water. All hypothetical as without cutting open the HW cyclinder, I won’t know what state it’s in.

What ever you do please change from the pre pay meters, it’ll save you a fortune over the cost of your heating of hot water and central heating.

As an example the house I’m in now had pre pay and changing it over meant I went from £85 a month to less than fifty!