Immersion heater or Gas boiler for energy savings?

[Jonboy13]

I am trying to reduce my energy bills (aren't we all!) and was wondering if it's cheaper to heat my water with the immersion heater or using the gas boiler. Obviously as it's summer the rads are off right now so there's no need to fire up the boiler unless I need hot water. I have an indirect cylinder by the way (water can be heated by both element and coil). Water is heated for about 1 hour once a day.

Anyone know which method is cheaper to run when the rads aren't on?

Thanks,

Jon

 

[corgiman]

gas as it heats up the water qickly as is direct

you electricity is supplied (in the main) by gas power stations

and its damn expensive

Thats my opinion

 

[chrishutt]

Corgiman is right. Roughly speaking electricity is three times the price of gas per kW of power input. The output you get with gas will be less, depending on the efficiency of your boiler, which could be anything between 90% (condensing) and 65% (oldish cast iron). And your electricity could be much cheaper if you have economy 7 and heat the water at night, but even in the worst case scenario gas will be a little cheaper than electricity.

Make sure the cylinder and pipework are well insulated. Check that the temperature set on the boiler thermostat is higher than the temperature set on the cylinder thermostat (normally 60°C), if you have a cylinder stat (if you don't, consider fitting one). Check your boiler efficiency at www.boilers.org.uk and if it has a poor rating consider upgrading to a condensing boiler. And finally check that you're energy supplier is among the cheapest (Uswitch, etc.).

 

[corgiman]

Corgiman is right.

I never get sick of hearing that, well the once in the blue moon it actually gets said anyway

 

[Alfredo]

Working in the council sector I get truly fed up with tenants telling me they turn the gas off in the summer and use the 'lectric' to heat the water cos its cheaper..."Who told you that?" I ask the reply comes back "me mate"..and its all downhill from there..I've taken to saying jokingly "well you must be bloody rich then"

Its an uphill struggle explaining that its gas what makes the electric..so they are paying for it twice..and only half of them believe you.

Other 'pearls' are tenants who have lived in a house for 10 years and never touched the roomstat..which is stuck on 30C...and they have NEVER touched it "No one ever told us what it was for" Cylinder stats whacked up to 80c when you KNOW you left it on 55-60c when you serviced it.."nobody's touched it love". There's also the ones that call you out at night only to find they have run out of gas..having assured the call centre they have got gas...

My all time favourite was the old dear who had changed to a cheaper gas supplier "its allright I suppose" she said.."but the gas hasn't been half as good since i changed".......Now try challenging her logic!!!!

I think its a dependency culture that creates most of these attitudes..but it keeps me in a job so I don't complain too much.

Use the gas..not the immersion

Alfredo

 

[Kes]

Hi,

Its an uphill struggle explaining that its gas what makes the electric..so they are paying for it twice..and only half of them believe you.

This isn't a valid comparison, The electricity generators buy their gas in billions of cubic meters (or whatever) directly from the Russians, so they're hardly paying domestic supply costs.

I used to leave our boiler on through the summer for hot water, but this year I'm using the immersion heater on continuously. It's very difficult to get exact figures, but I reckon we use a couple of units a day for the immersion, which is 15p. Now our boiler is fired by oil not gas, and I'm sure it would go through more than a litre a day for hot water, that's 37p or more. Some of the principles apply to gas as well. Hot how is the boiler area in summer? That's heat just going out of the window, so to speak.

With gas there is more chance of estimating fuel use than there is with oil. Why not use the boiler for a month for hot water, taking daily readings of the gas and electric meter. Then switch off the boiler and use the immersion for a month, continuing with the daily readings of the electric meter. Then play with a spreadsheet for an hour or two, and your fuel costs, and you should have a reasonable idea of the respective costs. Of course it's probably too late to do this now, as cooler weather approaches...

Rgds.

 

[Alfredo]

I agree its very difficult to draw an absolute comparison, but in general terms I would contend that the average household uses maybe two to three cylinders full of HW per day, with a recovery time of roughly 50 min, so I advise them to have the gas on for an hour in the morning..and depending on how many are going to require baths in the evenings..an hour or longer in the evening as appropriate. This has got to be cheaper than leaving an immersion running..except maybe on economy 7, which is of no use in the evening.

We also get a lot of people who leave the Hot water on 100% of the time..gas or immersion..on the basis that keeping it hot is cheaper than heating it from cold...and quite honestly I'm never quite sure how right or wrong they are, as the cylinder stat will only bring on the boiler when it cools. Cylinder insulation efficiency comes into play here of course, and most of the ones on our patch are pretty well insulated, so it might work I suppose.

I honestly don't have the time to start building speadsheets. I did tend to rely on the fact that for three years my wife was energy efficiency officer for the county, and so I tended to rely on the stats she brought home. She has cast off that particular mantle as of three months ago so my flow of often interesting (but not always useful ) information has stopped.

Alfredo

 

[Kes]

Hi,

Yes, comparisons are not only odious but almost impossible. A lot depends on household use, I doubt whether we use more on average than one cyl of hot water a day. Now that our daughter has moved out we are no longer prey to 30-minute-plus full-bore showers which end in recriminations. 'The water's run cold!' as if it's my fault! And we have a large h/w cyl too. Ah well, it's always the bill-payer who runs round turning everything off. I think that in the end you have to judge what suits yourself best.

Rgds.

 

[simond]

If Kes reckons he uses a couple of units a day for the electrical immersion he is an excellent example to us all in saving the planet.

2 units a day is 2kwh. That is equivalent to having a standard 3kw immersion heater on for 40 minutes each day. Even a top class unvented cylinder would lose this amount in heat per day if you didn't use any HW at all.

He didn't say he was bathing in the sink. I think we have a right to know.

 

[ChrisR]

Just round numbers, cost per cylinder heatup:

100 litres, 50º rise, uses 5.8kWh . About 50p of electricity?

100 litres is 630mm height of a standard 450mm (18") diameter cylinder, which is about the amount that gets heated by an immersion heater.

It's well worth putting extra jackets or even an old sleeping bag, over a cylinder, and insulating the pipes. It's surprising how much energy the standard foam sprayed ones lose.

(The sum is 100 x 4.2 x 50/ 3600)

 

[Kes]

Hi,

I can only get one foot at a time in the sink, it's not altogether a pretty sight.

When I started thinking about using the immersion heater for hot water instead of the oil boiler (which coincided with receiving a £730 bill for filling the tank) I started taking readings of the electricity meter every day. It's become an obsession. Anyway, in May we had a particularly cold and wet spell and the heating went on for ten days, and the immersion off. On those ten days the average daily electricity use was 12.07 units. For the corresponding ten days in June with the immersion heater on continuously, and blisteringly hot, the average use was 14.41 units. The huge h/w cylinder, by the way, is 60" by 18" and has a standard insulation jacket.

There are some quantifiers here. At this time the kitchen was being rebuilt, so there are no cooking costs included except for a microwave, kettle and toaster (and it's remarkable what can be conjured up with this triumvirate). Also I, and we, are trying to measure a variable. There's always someone turning a hot tap on, or doing some ironing, or deciding to wash everything, so a valid comparison is very elusive. Perhaps if I rewired the immersion heater to go through one of those usage meters I would have a better idea, but I'm not going to do that. I think I have to say that for the two of us, on a fixed price of 7.15p a unit, using the immersion heater is cheaper than puffing oil smoke up the chimney at 37p a litre. But then most people here seem to have the benefit of gas so perhaps the issue isn't so clear for them.

Now that we are fully cooking the average daily cost has risen. For the corresponding ten days in July the average daily use is 17.43 units. How much is the immersion heater I haven't the faintest idea.

Rgds.

 

[ChrisR]

Was the boiler on while you were also using the immersion heater? The (radiator) heating wouldn't have to be on.

The longest imm heater is 30 inches, so that's all that gets heated if it's mounted from the top. Most are 27". If only using the imm heater the quantity is so restricted you only just get a bath out of it, depending on temp.

It has its own thermostat so perhaps it was only topping up the heat from the boiler?

 

[Kes]

Was the boiler on while you were also using the immersion heater? The (radiator) heating wouldn't have to be on.

No, first 10 days (May 22 on) boiler provides heating and h/w, no immersion; next 10 days (June 22 on) no boiler, immersion on cont; last 10 days (July 22 on) no boiler, immersion on cont and ovens in use.

It's all a little selective. I could have chosen alternative ten-day periods which would have put a different light on things, but I picked the same ten days each month. The daily use doesn't seem to have any logic really, some days it swings wildly with no apparent reason. But I'm moderately happy with my lot.

Thanks to all.