Pre Heated water into Oil Combi

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So with fuel prices going super high, I am looking at some options to save on oil use.

I have a Worcester 12/18 Combi Oil boiler, feeding UF Heating system via an accumulator tank, and of course bathrooms for hot water.

I have access to 7Kw of free Electric from a Solar Farm with storage, so 7Kw is always available day and night. So I have used a 3Kw emersion heater in the accumulator tank, with a stat set at 50C, that is switched only when heating is called. This then heats the CH circuit and works awesome, the boiler burns less oil to heat the CH. Using the free electric to help the boiler along.

Now I was wondering can I use a small 3Kw water heater to pre heat the cold into the boiler. Again with a view of less oil used to raise the DHW temp.
 
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I was going to link you to another thread with very similar content but you've already been there..
7kwh/hour free- you lucky person.
Your best bet is to get away from the combi (which needs short high-energy bursts) and stick a thermal store in- the bigger the better within reason (500 ltr or more). This can run your heating and dhw, the boiler can chuck additional heat into it if needed but if you're getting 7kwh/h 24/7 from the solar setup it won't be needed very often.
 
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Thanks, my issue is space, otherwise that would be my first option for sure.

yes found the other thread after I posted, hehe.

Even if I can pre heat to 20 or 30 C would cut oil usage by loads I think.
 
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With free energy I'd compromise a bit of space- 500l store isn't massive (a bit bigger than a tall kitchen cupboard- 500l is only half a cubic metre after all). If you have any outside space it could go in a Wendy house!
 
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With free energy I'd compromise a bit of space- 500l store isn't massive (a bit bigger than a tall kitchen cupboard- 500l is only half a cubic metre after all). If you have any outside space it could go in a Wendy house!

I know, just impossible just now and also the spend defeats the object, I’m going to contact woster and see what they say. Hopefully even getting the inlet temperature to 20C will make a difference with a little spend. The 3Kw in the heating circuit is already reducing oil usage
 
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Fair point and yes it will. Another longer term item to ponder- your power setup would make an ashp a good fit.
 
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Pre heating secondary water won't really achieve a lot in savings. The only benefit I can see would be you may get a greater hot water delivery volume. The boiler is designed to give a temperature rise to the flow through the DHW heat exchanger, so you may be able to exceed the designed delivery volume.
 
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Thanks all, I am a person who loves data, and I have digital sensors on everything. I have already dropped usage from 9L per day to 6L per day by heating the buffer tank, remember my UFH runs at 40C only so the 3Kw heater does a great job. I have top of the range sensors and data logging so know exactly where my savings are.

Hence the looking at the data, would like to boost the DHW
 

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if you have a free supply of 7kw i would get an air source fitted tomorrow? you can get hybrid but who cares if you can have that much electric for free. you could have 2 units fitted and unless you live in a mansion all your heating and hot water should then be free
 
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How do they work? I’m in Scotland and thought they don’t work well up here?
 
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How do they work? I’m in Scotland and thought they don’t work well up here?
Witchcraft. You probably won't get the 4:1 efficiency generally quoted but that doesn't matter to you cos your source energy is free. ASHP running UFH is ideal, not sure exactly how the things heat dhw but it'll give you the benefit of 21kwh/HR (at a very pessimistic 3:1) for your input of 7kwh/HR. All for FREE!
 
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:(

not free then

costs thousands :eek:
Yeah there's an install cost, I've no idea what the current state of grants/deferred payments or other inducements is, every time I've looked the payback time has been in decades due to base electricity cost. If your base electricity cost is zero, payback should be about 4 or 5 years on a £5k install swapping from gas or oil
 

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