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 Post subject: What is the cheapest way to heat water?
PostPosted: Wed May 20, 2015 12:03 pm 
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If you're refurbing or building new, what is the cheapest way to produce hot water?

There have been a few discussions of various technologies individually, but it strikes me that there must be a "best" answer for a typical house in the Irish climate.

Air source heat pump?
Ground source heat pump?
Solar water heater?
Solar PV + immersion?
Grid + immersion? (Surely not!)
Something else?

By "cheapest" I mean TCO over the life of the equipment, including energy inputs to run the system (pumps, etc). Ignore time-value of money. Assume a typical house with a grid connection etc.

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 Post subject: Re: What is the cheapest way to heat water?
PostPosted: Wed May 20, 2015 12:09 pm 
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If you have easy access to timber or turf then I'd say a stove. It doesn't suit every home. After that Solar collectors. The most cost effective solution is a solid fuel stove, solar collectors and an immersion.

A modern well insulated house will also have enough space heating from that combination.


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 Post subject: Re: What is the cheapest way to heat water?
PostPosted: Wed May 20, 2015 12:12 pm 
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Coles2 wrote:
If you have easy access to timber or turf then I'd say a stove. It doesn't suit every home. After that Solar collectors. The most cost effective solution is a solid fuel stove, solar collectors and an immersion.

A modern well insulated house will also have enough space heating from that combination.


Thanks. Questions:

Solar collectors = solar hot water (not PV)?

The immersion runs from the grid and is a backup presumably?

And if you don't want to run a stove, is solar + immersion still the best combo?

Assuming the above, why do people bother with heat pumps?

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 Post subject: Re: What is the cheapest way to heat water?
PostPosted: Wed May 20, 2015 12:19 pm 
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Mantissa wrote:
Solar collectors = solar hot water (not PV)? Er, yes, you dumbo.

The immersion runs from the grid and is a backup presumably? Yes

And if you don't want to run a stove, is solar + immersion still the best combo? No, probably gas.

Assuming the above, why do people bother with heat pumps? So they can talk about it over dinner.


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 Post subject: Re: What is the cheapest way to heat water?
PostPosted: Wed May 20, 2015 12:22 pm 
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This is a topic I'm interested in.

Current set up in my gaff is an aged gas boiler ('Ideal' brand, late 90s model) heating c. 2000 sq ft (single zone), and an immersion providing hot water for the taps, (pumped) shower etc. Currently these are timed with basic mechanical one-day clocks.

Anyone any experience/thoughts on whether or not a modern combi boiler setup would provide efficiency in terms of gas usage on the heating, and over the immersion for hot water?

Or would I be better doing some draft proofing (there's quite a bit of exposure at the moment through external French doors etc) and insulation upgrades in the interim and examining the bills over the next winter?


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 Post subject: Re: What is the cheapest way to heat water?
PostPosted: Wed May 20, 2015 12:31 pm 
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Mantissa wrote:
If you're refurbing or building new, what is the cheapest way to produce hot water?



Large vacuum flask and bring it home from work. After the initial capital cost, it's entirely free (if sneaky). :twisted:

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 Post subject: Re: What is the cheapest way to heat water?
PostPosted: Wed May 20, 2015 12:50 pm 
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I looked extensively at this for our big fat renovation.

Our solution

1. Solar water heating
2. A big 300l insulated water tank
3. A combi boiler
4. Pressurise the ststem.

Hot water for showers and the hot tap is 40 degrees. During all but the coldest winter months or persistently dark days we are expecting the solar alone to keep the water tank at or above 40 degrees. If it drops below the combi boiler steps in to bring it up to the required temp on demand.
By pressurising the system the 3 showers in the house and taps should have good pressurised hot water all of the time.

We will not have an immersion heater.
While we will have a wood burning stove it will not have a back boiler as we donot antisapate it being required. It also obviously sucks a lot of heat energy from the stove which will be vented from the water tank if it's excessive.

I'll let you know how we get on.

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 Post subject: Re: What is the cheapest way to heat water?
PostPosted: Wed May 20, 2015 1:04 pm 
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Coles2 wrote:
Mantissa wrote:
Solar collectors = solar hot water (not PV)? Er, yes, you dumbo.

The immersion runs from the grid and is a backup presumably? Yes

And if you don't want to run a stove, is solar + immersion still the best combo? No, probably gas.

Assuming the above, why do people bother with heat pumps? So they can talk about it over dinner.


Thanks Coles, really useful. Just to clarify, when you say gas do you mean just gas, or solar + gas? I presume the latter.

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 Post subject: Re: What is the cheapest way to heat water?
PostPosted: Wed May 20, 2015 1:04 pm 
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Terra Incognita wrote:
By pressurising the system the 3 showers in the house and taps should have good pressurised hot water all of the time.


Thanks TI, but what do you mean buy "pressurise the system"? A opposed to what?

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 Post subject: Re: What is the cheapest way to heat water?
PostPosted: Wed May 20, 2015 1:08 pm 
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Mantissa wrote:
Terra Incognita wrote:
By pressurising the system the 3 showers in the house and taps should have good pressurised hot water all of the time.


Thanks TI, but what do you mean buy "pressurise the system"? A opposed to what?

Gravity...

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