Linking wood burner and combi boiler

[oldbutnotdead]

A theoretical scheme at the moment- just acquired (v cheap) a woodburner that does water heating as well- it'll run up to 8 rads and domestic hot water if required. Now I'm loving the thought of getting hot water from the woodburner but don't really want to have to light a fire when I want a bath. Plus when I'm away (which is quite often) the house will cool down a lot if that was the sole heat source.

So I'm looking at gas central heating anyway- how good are combi boilers at using variable temperature supply water for the hot water side? Thinking is to use the woodburner to heat an oldschool vented hot water cylinder with header tank, the output of which goes through the combi & thence to taps. If the cylinder water is warm then it'll only need a tickle from the combi (or maybe no input at all) to get it up to temp, if cylinder is cool/cold then combi will do the necessary.

Is this feasible (without spanking a fortune on weird things), are there particular combis that are good for this trick?

Cheers

 

[Dan Robinson]

Would need blending valves, pumps, hassle. Even then I'm not sure it will be compliant.

 

[oldbutnotdead]

Boo, I had feared this would be the case. Ah well, back to the drawing board

 

[PullerGas]

Ach don't listen to Dan he's all thermistors & no knickers!!

Search 'Heat Bank' & come back on when you're better informed. Enter Dr Drivel stage left??!!!

 

[Dan Robinson]

 

[Corgigrouch]

It can be done but it would cost you more than Dickie has stashed under his mattress..

 

[PullerGas]

It can be done but it would cost you more than Dickie has stashed under his mattress..

What a Heatbank & a plate heat exchanger, pump etc?? Don't think so Rouchy???!!

 

[Corgigrouch]

Come on Dickie, your older and wiser than that...

 

[MrTherm]

A "low loss header" would be a viable solution and not too expensive. It would be totally automatic in its output distribution and to its heat sources input.

For example a 2" LLH can be had for about £180 or 1 -1/2" about £120, would give automatic "no valves" blending.

regards

 

[Corgigrouch]

LLH or a Neutraliser would work well.. But don't forget that you must provide Back end protection, heat resistant F&E tank, plate to link the open vent to the pressurised system... Then you have to decide if you just want to link in to the heating or provide hot water too (Convert the combi to heat a cylinder) and feed the Solid fuel to the cylinder....The cheap boiler stove suddenly doesn't seem quite so cheap

Some combis will take preheated water some won't...Which combi do you have?

 

[oldbutnotdead]

Well this is all very interesting- cheers for all the input. The Wiki is useful in generic terms especially the Thermal Store concept.

Initially the plan was merely to use the spare heat from the woodburner for DHW and leave the heating alone. But looking at Thermal Stores, not sure how the control system would work but it looks as if I could use direct from the woodburner to the store and indirect from the combi to the store for heating (or the other way round or is that going to be hopelessly inefficient). Haven't found yet if combi and woodburner could both be direct into the store or whether that would need lots of control gear.

DHW would by the look of it need a separate heat exchanger and then route the output of it through the combi.

I don't have a combi as yet so the sheet of paper is blank- place hasn't got radiators or DHW so I can do what I like, there's space next to where the fire will be going for a reasonable size thermal store (convenient alcove next to the chimney in the kitchen). Need to have a good read through the wiki when I'm not about to head out for a night shift.........

Ahhh, the Neutraliser does look suitable for running the heating system- wiring looks interesting as does the pipework. So that's heating looking doable- in my ideal world I'd like the instant dhw that a combi can provide but still be able to take advantage of the 'spare' heat from the woodburner. So, combi that will take variable temperature supply water for DHW (and are sufficiently subtle to keep the output temperature more or less constant) needed. I'll work out the actual thermal demand later........

Low loss headers look interesting.....more research needed. Again, ta all- given me plenty to chew on

 

[Corgigrouch]

If you ain't got a combi, then don't get a combi.. A thermal store is then a better option if you have room for the store and you can have hot water at mains pressure.... Assuming your water pressure is ok, if not a tank in the loft and a cylinder. The Neutraliser is designed to link in two or more heat sources but I see no reason why a LLH wouldn't do the job.. If you use a bit of tupperwear, then you can have your system fully automatic but if you light the stove, then that will take priority and the gas boiler won't run...

I think that Dan has a thermal store for sale..

 

[Biggles..]

If it's being used purely for hot water which is what your post infers, then certain combi's will indeed allow reheated hot water through them.
Quite surprised @Dan_Robinson didn't tell you the intergash is a prime example of one that can.

My atag at home does, takes it's water from a solar heated cylinder.

Can be fed direct but I decided to use an intasol valve. £150ish quid, hardly a fortune.

Remember a TS/Dunsley/neutraliser/LLH/buffer/heat bank/plate heat are all options if you want the stove to do the rads.

 

[Dan Robinson]

Wanted to keep it short and sweet

 

[oldbutnotdead]

Cheers all- before your useful hints about neutralisers and low loss headers I thought linking the heating would be a chew but the hot water relatively easy. Looks as if the heating is the quick & easy, the DHW needs a bit of thought regarding cost effectiveness, lifestyle etc.