Do you have access to free, seasoned wood fuel?
Space to store it, and the time to prepare it for burning?
If so, then go with the WBS.
Keep the space-heating demand to a minimum, and you will be OK.

However can you see yourself stoking, cleaning and maintaining a WBS in 10-15 years, if not perhaps ASHP would be a better option?

What is your predicted overall heat loss, and FEE?
Good luck..

Posted By: olliedWe are planning to have MVHR and two wood stoves as the only space heating.

How are you planning to circulate the heat from the wood stoves around the rest of the house?

ollied,

MVHR tends not to be good at moving heat energy around dwellings...

FEE - Fabric Energy Efficiency; the thermal performance of the building fabric. How much heat is lost through the walls, floor, roof, windows....

If you have an open-plan bungalow, the WBS + MVHR 'might' work if the WBS(s) are situated correctly?
ASHP + ufh results is larger heat emitters albeit at lower temps, but in the correct place.

Where in the UK are you?

Good luck...

It's a question of insulation and air-tightness dictating how well the house holds its heat. If it does so really well overnight, then you may not resent getting up to fire up a stove. If it does cool significantly (and it shouldn't if you build fat and tight!), and you want heating that comes on before you get up, then a log gasification boiler, accumulator and UFH may fit the bill, separating burn time from heating time.

Nick

Chris, what's the brand/model of your MVHR with a heating element? Will see if there's something similar available in the UK...

Mmmmm, maybe something awry with our calcs, tho fairly sure the 4.8kw peak was right, will check.....

Posted By: olliedWe are planning to have MVHR and two wood stoves as the only space heating.

My feeling is that you will simply roast next to a WBS in a well insulated house and air tight house. MVHR does not move heat around very well. I'd go for a simple UFH system off a big tank. How are you supplying DHW?

Borbin, plan for solar thermal with elec. immersion back up. I am a bit worried that it'll just be too hot, have friends running space heating and hot water off woodfired range and their kitchen is always too hot. When you say simple UFH what would you drive it with?

Thanks all for the comments/suggestions....

Posted By: olliedWhen you say simple UFH what would you drive it with?

It's a tricky one Ollie, I would suggest that you get good estimates for your heat demand and heat load, then when you are confident of what the numbers are you can start looking at the alternatives.

If your previous calculation is correct and your total heat demand is 2300kWh/a then what would that cost you with direct electricity? (I'm guessing at a unit costing 15p so 2300x0.15=£345)

If that is the case then say a heat pump with a COP of 3 will save you £230 per year so that £16,000 you quoted earlier will take over 60 years to pay back, so that makes no sense as the heat pump will never last that long anyway.

If your heat demand is that low then you are not going to find anything with a capital cost so low that it will give you a good pay back compared to direct electricity.

You could install electric under floor heating in your slab and run it on E7 working like a huge storage heater you will only want to heat the slab by a degree or two overnight and it will slowly release the heat to the house during the day.

Or you could install some simple thermostatically controlled electric panel heaters and run them on normal rate electricity.

Run your DHW tank on E7 in the winter and install some PV to power the immersion in the summer and provide some extra power for general domestic use.

Timber frame is normally built off a concrete slab. Apart from the obvious structural function, this provides useful thermal mass & a ready made large surface area heat emitter. What are you planning for foundations?

David

Posted By: ollied Maybe with a WBS with a back boiler for emergencies??

Nope, in a low energy house wood burning stoves give rise to two problems. One is overheating as already mentioned and the other is that cold air tumbling down the flue makes the stove into a cold radiator any time it is not lit.

http://canmetenergy.nrcan.gc.ca/software-tools/hot2000/84

That's a link to a heat loss calculator that "Paul in Montreal" frequently mentions on here, Someone else posted a similar type spreadsheet on here recently but I can't find it with a quick search at the moment.

My estimates were done in the Passive House Planning Program (PHPP) but that costs quite a few bob to get done professionally.

Ollied. Our 2 year old 1.5 storey "chalet bungalow" is reasonably well insulated approx 120m^2 and has the following: 5kWh wood burner for space heating. It does not roast us as we are able to turn it down. We have underfloor heating (not used) running off calor combi boiler which is our source of hot water for shower. MVHR (not used). Two big kettles on stove for hot water when stove on. Kettles on gas cooker for hot water through summer. Glazed roof light accidently acts as air stirrer in front room in winter. 4 inch hole in floor under kitchen units brings fresh air in, bedroom windows snicked open.
Our brick chimney acts as overnight heatstore, at the moment, during the day, stove on 1 log every 90 mins maybe, temp at 19-20 c ish.
47kg gas bottle lasts 3.5 months @ £65 a go. expect to use 8-10m^3 of very loosely stacked logs over average winter, but who knows what sort of winter we're going to get?
There's only two of us and so it's all dead simple. We're in Hampshire.

Posted By: olliedDavid, timber frame co's we've spoken to have talked about concrete pads rather than a whole area slab, though I appreciate that we'll be missing out on the mass effect...

Slightly OT but firstly where are you? Secondly, you will therefore be looking at a suspended timber floor. These are notoriously difficult to insulate and seal for air tightness. You really do want a solid floor with loads of insulation. UFH is a very cost effective solution especially when run 'simply' i.e. at low temperatures about the same as the ambient you are trying to achieve. Best to have 2 zones, one for living and one for sleeping. If you are looking at Solar Thermal then look at the Akvaterm cylinders. However, I am not yet convinced I would not have been better with PV and 2 big immersion heaters. Time will tell (still need to get the ST connected up).

Or you could buy a few of these http://tinyurl.com/kj64dv7 (4.7kW max output ones are best cost/COP trade off, or there's a bigger Mitsubishi -Electric-, not heavy industries, one) for a fraction of the cost of A2W with UFH.

If you do, let us know how well they work! Especially whether you reckon they get anywhere near their 5+ COPs - no data on that for rainy old UK, but they should do better than A2W.

Do you have other means of ventilation? How is that incoming air heated?

David

Davidfree...Air comes in via airbricks under a suspended engineered timber beam floor ( packed with recycled newspaper) then up through hole in floor under kitchen units. Also windows in bedroom and bathroom kept on snick. This costs us in logs rather than leccy, maybe one log a day. It is not draughty!, but we do close up a bit more when the below zero in the day days are upon us.

Ollied. Two major things I would change now if I had the chance. I didn't realise that you could insulate in/under the slab/ring beam, so would revisit to see whether direct contact with ground or insulated is best.

Also we have insulation between brick face and flue on the internal elevation, so lose the chance of using chimney as a radiator. (This might be against regs?)