jlparsons
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| posted on 6/2/09 at 11:07 PM |
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Combi boiler
I've got a gas combi boiler (about 15 years old) running my shower, and I'm wondering this...
When the water going into the boiler is relatively warm (ie in the summer months), will the boiler reduce the gas usage to give the same amount of hot
water but use less gas? Or will it increase the flow of the water instead and use the same amount of gas?
My money's on option two, but I thought I'd ask to see if anyone knows?
Thankyou again to the suppository of all knowledge that is locostbuilders. 
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spewing
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| posted on 6/2/09 at 11:33 PM |
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The only control on the flow is how much you open the tap.
At 15 years old at full flow the boiler will raise the temperature of the incoming water by an amount depending on the size of the boiler so the
warmer the incoming water the hotter the outgoing water.
Reducing the flow (turning down the tap) will to a point as the same amount of energy to a smaller volume of water giving hotter water.
Kev
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jlparsons
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| posted on 7/2/09 at 12:15 AM |
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Thought so. Renders the idea of drainwater heat recovery a bit mute, I'll only get a higher flow rate on the shower rather than better
efficiency. Worth a check anyway! Cheers mate.
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fatfranky
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| posted on 7/2/09 at 12:38 AM |
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I thought that mains water supply pipes were about 1.5 metres below ground to maintain a steady temperature. i.e. do not freeze, do not warm up
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jlparsons
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| posted on 7/2/09 at 02:01 AM |
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done a bit of research - apparently some modern condensing combi boilers (known as "fully modulating" are able to vary their flame. This
means i could use a drainwater heat recovery system as in the previous post. Also it means you could use a solar hot water system.
Something to bare in mind when i put in a new boiler, which shouldn't be too long!
Any resemblance to real persons, living or dead is purely coincidental. Some assembly required. Batteries not included. Contents may settle during
shipment. Use only as directed. No other warranty expressed or implied. Do not use while operating a motor vehicle or heavy equipment. Subject to
approval, terms and conditions apply. Apply only to affected area. For recreational use only. All models over 18 years of age. No user-serviceable
parts inside. Subject to change. As seen on TV. One size fits all. May contain nuts. Slippery when wet. For office use only. Edited for television.
Keep cool; process promptly.
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iiyama
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| posted on 7/2/09 at 08:18 AM |
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Vaillants are fully modulating and can actually vary the heat output by quite a margin.
Solar hot water and combi's will work, but are not as efficient as a system boiler and an unvented twin coil cylinder.
If its broke, fix it. If it aint broke, take it apart and find out how it works!
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jlparsons
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| posted on 7/2/09 at 10:09 AM |
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I'll look out for a vaillant then I think! That's what I've got already but it's about 15 years old now, and iirc it's
about 60% efficient when new!!
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JoelP
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| posted on 7/2/09 at 10:56 AM |
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my best idea so far regarding getting heat back out of waste water is to have an underpowered electric shower with a good heat exchanger. You just
keep upping the flow as the waste gradually gets warmer.
Heat exchangers are quite efficient nowadays, on grand designs recently they had a chap with an air heat scavanger that got about 98% back.
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jlparsons
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| posted on 7/2/09 at 01:57 PM |
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I'm thinking of making my own heat exchanger doe to the cost and size of the commercially available ones. Got a couple of ideas, might use a
sealed large diameter drainage pipe with microbore copper running inside, run it along under the floorboards between the joists. It has only a single
wall between foul and fresh, but it'll be more efficient for it and it's only going to feed the shower so what the hell.
I see what you mean about the electric shower, that would be an efficient solution. Wouldn't fit in so well with my long term plan of putting
in solar hot water though.
[Edited on 7/2/09 by jlparsons]
Any resemblance to real persons, living or dead is purely coincidental. Some assembly required. Batteries not included. Contents may settle during
shipment. Use only as directed. No other warranty expressed or implied. Do not use while operating a motor vehicle or heavy equipment. Subject to
approval, terms and conditions apply. Apply only to affected area. For recreational use only. All models over 18 years of age. No user-serviceable
parts inside. Subject to change. As seen on TV. One size fits all. May contain nuts. Slippery when wet. For office use only. Edited for television.
Keep cool; process promptly.
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