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Gas Boiler v Immersion Heater
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# 1
Brommers
Old 23-07-2008, 12:16 PM
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Default Gas Boiler v Immersion Heater

With the current gas prices I was wondering how the economics of using timed immersion heater v gas boiler work out. We have a condensing gas boiler and for hot water have it on twice a day for 2 hrs. Had the boiler down last week and on immersion for 2 x 1hr the water seemed hotter than with gas. Just the 2 of us so not a high usage of hot water. Any thoughts appreciated.
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# 2
espresso
Old 23-07-2008, 12:24 PM
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Originally Posted by Brommers View Post
With the current gas prices

So how much to you pay for your gas per kWh compared to your electricity?

I was wondering how the economics of using timed immersion heater v gas boiler work out.

Gas will be cheaper.

We have a condensing gas boiler and for hot water have it on twice a day for 2 hrs.

You should not need it on for more than about half an hour to heat a tankful of water.

Had the boiler down last week and on immersion for 2 x 1hr the water seemed hotter than with gas.

That would depend on what temperature the thermostats are set to.

Just the 2 of us so not a high usage of hot water. Any thoughts appreciated.

Try setting the gas boiler for less on time e.g. 30 minutes each time.
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# 3
Mazio
Old 23-07-2008, 3:38 PM
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There are other factors you should consider, although gas is normally cheaper with a modern system.

1) How close is your boiler to the hot water tank.If its an indirect system (with pipes from your boiler to the tank with a coil in then back to the boiler) the further away will require more gas and water to heat as it needs to heat the water in the pipe too and this will also cool down quicker..

2) Most gas boiler thermostats will also keep cutting in to keep the water temp up in the heat exchanger inside the boiler up to temp even if the hot water in the your tank is OK so potentially use more gas this depends how yours is controlled..

3) How well insulated is your hot water tank as the immersion heater once upto temp and dependant on your requirements can be OK for hours before it switchs on again.

The only other way is to heat your water using the 2 systems in your house for a few days each and check your readings at the meters. I have started to use an immersion and have found it slighlty cheaper because my CH boiler has been moved into an extention and is now over 20' away from the tank and use to take 2 hours to heat my 147 Ltr hot water tank this how ever could change when my son returns from abroad and we use more hot water.
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Last edited by Mazio; 23-07-2008 at 3:50 PM.
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# 4
espresso
Old 23-07-2008, 4:20 PM
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Quote:
Originally Posted by Mazio View Post
There are other factors you should consider, although gas is normally cheaper with a modern system.

1) How close is your boiler to the hot water tank.If its an indirect system (with pipes from your boiler to the tank with a coil in then back to the boiler)................

Should not make much difference to a fully pumped system, 20' is no distance for a boiler capable of heating the whole house!

2) Most gas boiler thermostats will also keep cutting in to keep the water temp up in the heat exchanger inside the boiler up to temp even if the hot water in the your tank is OK.............

Most boilers will only fire up when heat is called for e.g. the stat on the water tank actually requires heat.

3) How well insulated is your hot water tank as the immersion heater once upto temp..............

Same applies to either method of heating the water but the OP is talking about timing the heat input, not on all of the time.

The only other way is to heat your water using the 2 systems in your house for a few days each and check your readings at the meters................

Are you comparing the actual running cost for kWh used or units used?

and is now over 20' away from the tank and use to take 2 hours to heat my 147 Ltr hot water tank...........

Sounds like there is a problem with your system if that is the case!
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# 5
Brommers
Old 23-07-2008, 11:16 PM
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Thanks guys for your comments. Will try the gas boiler for shorter time for a few days. It has to be taken out for some building work next week so will be able to monitor the immersion system properly and see how it goes. I suspect that when there is no requirement for central heating it might be the best way but it would be useful to try and prove it one way or another. Point taken that units need translating into actual cost.
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# 6
Mazio
Old 24-07-2008, 7:43 AM
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espresso just to claify a few points I am not disputing what you have written BUT

Even with a 95% condensing boiler it will not translate into heating your hot water 22mm pipes full of cold water running for instance 20ft each way will need to be heated first this then has to be transported to the calorifier which in turn is loosing heat so now you will not be achieving 95% from the boiler as this cools you will need to heat everything up again to transport to the hot water tank heat exchanger if you have an indirect system.

You also need to have had the installation fitted with all the modern guide lines not just the boiler eg delivery and control system needs to also be 95% to give you the heat transfer and alot of UK systems will not have this so you need to also consider install date as I said my system is from the 80s and I then extended the house and moved my boiler.

Iam not disputing that gas should be cheaper but it is also dependant on the other factors. You cannot just use text book calcs and assumptions.

My system does not have any control at the tank end I can only control at the boiler with the water temp at that end this was how alot of installers were fitting at that time. It can cost £100s to retro fit control at the tank and £40 to fit and use an immersion which could be just as cheap in SOME instances.

So I was suggesting taking readings at the meter and do a cost comparisons for your system as this is the only real way of knowing which one to use, although gas should be cheaper.
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# 7
espresso
Old 24-07-2008, 9:19 AM
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Quote:
Originally Posted by Brommers View Post
It has to be taken out for some building work next week so will be able to monitor the immersion system properly and see how it goes. I suspect that when there is no requirement for central heating it might be the best way but it would be useful to try and prove it one way or another. Point taken that units need translating into actual cost.
Even though electricity is at least three times more expensive per kWh! Better to use your gas boiler all year round.

Neither of you has mentioned cheap rate electricity tariff e.g. E7 etc. and that is the only way that electric would come close for domestic water heating compared to gas.
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