Gas cost - water vs heating

Sueinbirmingham

This is a question relating to whether hot water accounts for a lot of gas usage, but bear with me while I put it into context.

We've moved house have yet to do more insulation-wise, (e.g. most of the loft is well-insulated but not all, there are rooms needing thicker curtains, not all the windows are double-glazed and some are ideal for a bit of simple home-made secondary glazing with sheets of plastic and there are pipes that could do with being properly lagged where they go through places that don't need heating) but in the meantime, the gas bills are horrendous. (I have an idea what they were like before because I know the previous residents.)

We have an old-style boiler and hot water tank. We've switched off the immersion heater on the tank.

We're heating the living room, the kitchen, the bathroom one bedroom for a disabled family member. For part of the day, we leave the other bedroom doors open to let the heat go from that bedroom into the other bedrooms.

There are thermostats on the rather old-fashioned but sturdy boiler and on the radiators. None have actual temperature markings and there's no house/wall thermostat.

A bit of experimentation has shown that turning the radiator and boiler thermostats down so they're almost off but leaving the heating on all the time instead of having it going on and off has reduced condensation and made the place feel a lot warmer without significantly increasing usage (it's a little hard to tell because of changes in weather in the short time we've been here). I plan to experiment with just how far down I can turn those thermostats but I do want heating on because of the disabled family member.

I can experiment with just how far I can turn the thermostats, of course.

However, I'm beginning to suspect that hot water accounts for a lot of the gas usage. There's an electric shower, so it's not a question of lots of bathwater, and we can be a bit more careful about not running hot water when washing up etc., but there has been a lot of cleaning to do since we moved in.

So here we come to the crux of the matter. I'm hoping there are people out there who've themselves looked at this.

I've been used to using a modern combi boiler that only heats water as I use it, but I'm rather guessing that keeping a tank (fully insulated) of water hot costs quite a bit of money.

Is it plausible that the hot water usage is accounting for a high proportion of the gas usage? If so, does keeping water hot in a tank when I'm not using any also cost a lot?

I'm aware that like with the radiators I can experiment, but I thought others here might have experimented with this. Apart from anything else, switching heating to 'on' and turning dials on radiators and boiler right down was easy, whereas altering the time settings for the water on the electronic timer is a nightmare.

I hope you will all forgive me if I don't quote actual usage. I'm rather scared of "you shouldn't be that profligate with heat" type replies.

Cardew

Sueinbirmingham wrote: »

Is it plausible that the hot water usage is accounting for a high proportion of the gas usage? If so, does keeping water hot in a tank when I'm not using any also cost a lot?

.

Your question is really just addressing the heat loss from a hot water tank.


As you state your HW tank is well insulated those losses are surprisingly small. Modern HW tanks are tested to a British Standard(BS) and a full tank with water at 65C will typically lose 1.5kWh to 2.0kWh in 24 hours. On some tanks you can read the actual loss stamped on the tank.


Now given your tank is unlikely to be full of water at 65C 24/7, the losses are likely to be far less than 2kWh - typically 1kWh if heating to your tank is timed. So approx 4p a day.


It is also pertinent to point out that those losses are not really lost as the heat warms the fabric of the house; which is why many HW tanks are in an airing cupboard.


Of course if you use a lot of hot water it can be expensive, but would be with a combi as well - it is not attributable to the HW tank.


Finally there is the question of heat losses from the pipes. that of course depends on the layout in the house - it could be worse or better than a combi. In fact a major criticism of some combis is the amount of water that has to be run-off before warm water appears at the tap.

victor2

Heating and maintaining the temperature in a hot water tank can cost more than you think, but it obviously depends on many things, including how well insulated the tank is, what it's capacity is and how much water you draw off each day.
With many older style systems, the hot water is on whenever the heating is on. I have that type of system - just as an example, our house was empty for about 3 weeks in October and I left the central heating timer to run about 7 hours a day (in two sessions), should there be a cold spell while we were away. The heating thermostat was turned low and the heating was never required. But it still used an average of 26kWh per day through the pilot light (it is an old boiler!) and heating the water tank. The pilot light accounts for 4-5 kWh per day. The boiler temperature was set at its mid point, which I find is enough for just hot water in the summer, but not enough when the central heating is used.

JJ_Egan

What i have found a big influence is using small to moderate amounts of hot water as its replaced in your hot water tank by cold water .

Sueinbirmingham

Thank you for all the helpful replies.

Cardew's reply gave me food for thought about heat loss through pipes. The boiler is in an outhouse not in the house. Time, I think, to do something about lagging the pipes leading from the boiler to the house.

I don't think that for the time I'm likely to be here it would be cost-effective to replace the boiler with an indoors combi-boiler, but a bit of help with this and that helps, so I'm grateful for the replies. I'm not sure if there's anything more anyone else could add, but if there is, I'll come back and read it because I'd rather not go bust just on the back of my gas bills!

jamesd

Given that the boiler is in an outhouse those pipes could be a substantial heat loss source. Also means that the boiler's heat losses are probably not warming anywhere useful. You might want to check that it is a decently insulated boiler, just in case it's a really old one.

Heating hot water can be expensive. It tales about 0.05kWh to heat a litre of water from 20C to 60C. About 21 litres per kWh.