combi boiler with cylinder and wood burning stove

[zimbo]

Hi

AM about to refurb our house and need some thoughts on ideas for heating and h/w.

I wanted to incorporate a wood burning stove as have cheap wood source to heat water either for the C/H or water or both.

We had a combi boiler in our last house and it managed to feed 2 showers ( 1 in loft) but now are reducing new house to 1 bathroom.

Can the combi be installed in the loft???
can the combi heat the hot water and central heating when wood burning stove is not being used?
I know that the combi can be used to feed part of the house and the cylinder to do the shower for example!!!
We were going to have the cylinder in the loft as well and would it work off a direct c/w feed as i hate the idea of the tanks up there not sealed!!!

Many thanks, hope it is explained well enough

 

[SimonH2]

I would suggest you consider a thermal store or heatbank. Your woodburner then heats the water in the store directly - by gravity if you can arrange things in the right place. You then use a heat-only boiler as a secondary heat source when you don't have the woodburner running.

Because it's open vented, you don't have the issues of having an uncontrolled heating appliance connected to a pressurised water store as you would with an unvented cylinder.

You can then run the heating from the store, and the DHW from the internal coil (thermal store) or heat exchanger (heat bank). You get mains pressure hot water and no need for a header tank (but you do need a small F&E tank for the store.

The main downsides are :
1) most plumbers will have a long "sucking through teeth" before suggesting you need to rip it all out and replace it with a combi.
2) for the same reasons, a lot of plumbers will treat it as something crash landed from another planet and won't be able to diagnose even simple problems.
3) for what they are, they are "rather pricey".
4) as few people understand them, you may find it hard getting sensible advice

The upsides are :
1) They make the plumbing simple. The OV store acts as a neutral point so you can have different flows (woodburner loop, CH loop, boiler loop) that don't interact.
2) Because of this, you can fit TRVs on all your rads and a modulating pump. When the rooms are warm, the CH flow rate will drop off as the TRVs close, and the modulating pump will just back off - so you get comfort AND a quiet system. There is no need to keep a minimum flow rate to keep the boiler happy for example.
3) You still have stored heat, and the option of immersion heater for backup though that's somewhat less important when you've a woodburner. It's really useful given the (lack of) reliability of gas boilers if your only source of heat is the gas boiler.
4) As mentioned, you get DHW at mains pressure (or whatever you set the pressure reducing valve to).

If you are interested, then you may find it useful popping over to the Navitron forum where you will find a lot of information - there is a biomass forum there.

I fitted a thermal store in my flat at the end of last year. There's a thread about it and you'll find a schematic of the plumbing about half way down the first page (note the complete absence of motorised valves !). To add a woodburner, it's two more pipes (cold from the bottom of the store to the bottom of the woodburner, hot from the top of the woodburner to near the top of the store) - none of the CH or boiler circuit changes. There may be a need for some stuff around the woodburner, I'm not familiar with them, but guys over in the Navitron biomass forum will be able to help you.