economic way to heat water

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Ollie11

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hello. any thoughts on the most most economical way to have a constant supply of hot water in the home? available options are gas central heating on full or part time (with the thermostat turned down) or the immersion on to "sink" full time.
 
It's cheaper to heat the water tank with the gas. However - I haven't compared that to heating with just the sink option. I've checked the appliance calculator on the esb web site and they don't have it listed. I don't have easy access to my meter to check. Based on the appliance calculator to heat one tank a day from cold with the electric emersion is 68 euro per 2 months!

However, really you're comparing the cost of heating one tank with gas to heating the tank with electricity. It's easy to check the meter for the time to heat up the tank with each. It will be approximated with the electric (take away roughly the other appliances by looking at the average)

For me there is a 5x difference in cost, but that's comparing the figures on the esb site for a full taken with my own metering for 15 min with the gas - doesn't heat it fully, but sufficient for me. So it's not an apples to apples comparison - but good enough that I'm using gas! - My boiler is 10+ years old, really not that efficient, but even with that, far cheaper.

If you want hot water check the following:
Check thermostat in hot water tank - no point in over heating water
Check insulation - pipes, lagging jacket - or factory insulted tank far better - this won't reduce price of heating tank, but less re-heats required.
Just heat the water, don't heat the radiators - can easily switch between them.

Ideally:
Is solar an option?
If not, get a high efficiency gas condenser boiler (20-30% more efficient)
Consider a boiler that heats the water on demand instead of a hot water tank. More expensive than standard boiler - but may save you in the longer term.
 
We have night saver electricity and our immersion heater is on a timer. It's 2kW ("sink") and comes on every morning for 30 mins, so it consumes 1kW/h per day (2kW*0.5 an hr). On night saver that's 7c a unit, or 7c a day, by 365 = €25.55 a year. That's enough for 2 gravity fed showers per day and bit left over for general use.

If the immersion was set to "bath" (5kW) it would cost €63.88 a year.

I don't believe it's cheaper to heat water by gas any more (unless the central heating is on anyway) as you end up heating the water in the whole system, which is let cool down again and therefore a waste.
 
rockofages said:
I don't believe it's cheaper to heat water by gas any more (unless the central heating is on anyway) as you end up heating the water in the whole system, which is let cool down again and therefore a waste.
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A lot of people seem to consider the tank of hot water provided when the heating is on anyway as free for some reason!

New energy efficient washing machines only use a cold feed, as it is generally more efficient to heat the water in situ on demand rather than have it sitting in a tank for hours. It also loses heat in the piping run.
Leo
 
If you are running the heating, you don't run it any longer to heat the tank at the same time. Maybe I'm missing something.
 
It requires energy to heat a tank of water, this is the same amount of energy whether you are using gas or electricity. When you run this off the central heating, the temperature of the water being circulated to the rads drops as it travels through the coil in the water tank. So you end up needing to leave the central heating on that bit longer to raise the temperature of the house to the required level.
Leo
 
Have you thought about getting a timer on the immersion?

Then you can set it to heat water a few times a day when you think you need it.

One of the ones with the fiddly multiple settings (the clock ring with the push in tabs) is probably better as you might want it on three or four times a day.

Also, check what temperature you are heating the hot water to - plumbers seem to leave the default at almost boiling, which surely can't be that efficient.
 
Leo said:
It requires energy to heat a tank of water, this is the same amount of energy whether you are using gas or electricity. When you run this off the central heating, the temperature of the water being circulated to the rads drops as it travels through the coil in the water tank. So you end up needing to leave the central heating on that bit longer to raise the temperature of the house to the required level.
Leo
Click to expand...

Ah, that makes sense alright. I've never noticed that myself because the house heats so fast. But of course it must take more energy.
 
Most houses have the ability to just heat hot water only from the central heating boiler. I.E the radiator circuit is shut down. I rarely use my immersion. Next time you have it on watch your meter spin.
 
DavyJones said:
Most houses have the ability to just heat hot water only from the central heating boiler. I.E the radiator circuit is shut down. I rarely use my immersion. Next time you have it on watch your meter spin.
Click to expand...

If you turn of all the rads and turn on the boiler does this use the same amount of gas as if you had a seperate setting on your boiler for turning off the central heating circuit?
 
I don't know if this is an option for you but in my apartment gas is used to heat the water "on demand" so when you turn on a hot tap the water is only heated as you need it. I find it efficient for me anyway!
 
mickpyrmont said:
If you turn of all the rads and turn on the boiler does this use the same amount of gas as if you had a seperate setting on your boiler for turning off the central heating circuit?
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You are shutting down the radiator system the same, although it is a pain to shut off the radiators (you need only shut down one valve on rad to stop circulation). This will save you money as the amount of water to heat has been decreased.
 
I have a question about using the immersion heater that can't be answered on the ESB website. If you leave the immersion on all the time it is only being used to keep the water hot and not heating up a tank from cold (except for the first time you turn it on that is). Is there any way to calculate if it is more efficient to leave it on all the time than to heat the tank from cold even if only a few times a week? The ESB calculator assumes that you are heating the full tank from cold.
 
Voyager,
I was just going to ask the same question! ;)
At the minute we leave it on all the time (no timer switch), would it be worth our while getting a timer installed?
 
is this any help?. 1 BTU (British termal unit) is the amount of energy needed to raise the temperture of 1 pound of water by 1 degree F.

1 BTU = 3.412 watts
1 pound = .45359237 KG
1 litre of water = 1.01 kilograms
Degree F = 5/9 degree C

Standard cylinder volume is approx 135L

I think if these are applied in the right way you will get your answer.

Any mathematicians?
 
Voyager and zohan, I don't have the capability to work out the figures, but unless you have a tank that loses zero heat through radiation (is lagged to death), you will lose out by constantly topping up the temperature.
 
One other consideration with a tank is to look at the temperature the water is being heated to - by default many tanks seem to be set very high - 80C on my father-in-laws. As most of the hot water ends up flowing down the sink, this is a waste. There's usually a screw switch under the plastic cover at the top of the immersion coil that can be adjusted to reduce the maximum temperature the water is heated to. Also a handy thing to do if you have small children to prevent scalds.
 
DavyJones said:
Any mathematicians?
Click to expand...

Do we want to get really complicated and start adding in usage patterns and temperature loss over time from the cylinder? So I'm certainly not volunteering... :D

I think the best way to find out for sure is to get an energy meter and monitor for a standard week with each method. You'd need to get this wired in to the immersion circuit though.
Leo
 
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