Hi All

I would really appreciate some advice. My wife and I are converting a very small semi-detached thatched cottage. It's a 2-up, 2-down construction, with total floor area 46 m2. It will be renovated and insulated to modern standards (I think roughly 80 mm insulation everywhere). It's in the countryside.

We're also going to install a wood burner in our own extension, which is not well-insulated.

Our questions:

(1) We're installing a MVHR unit (in a confined space in the cottage roof cavity). Can anyone suggest some good brands? Our insulation expert suggested a Nuaire MRXBOXAB-ECO-LP2 because it’s a low-profile unit.

(2) Since we will have the MVHR unit we have been advised that we need a wood burner rather than an open fire. When I last looked into wood burners (10 years ago) I was told that a Clearview was much better than any other stove because it has an intermediate air setting where heated air effectively burns up the smokey gassy emissions, reducing pollution and giving more heat to the room. Is this real and important?

Any suggestions for good MVHRs and good wood burners? And is there any special technology on Clearviews or any other stove that makes an important difference?

Thx to all

Patrick

Posted By: PatrickSSWe're installing a MVHR unit (in a confined space in the cottage roof cavity)

Make sure you understand how much space is needed for access to clean/change the filters and heat exchanger.
Also don't underestimate the space required for ducting. And if it isn't inside the thermal envelope, you'll also need to allow a lot more space for insulation.

Things have moved on a bit in the 10 years since you last looked into wood burners. If you are going to have MVHR then I presume that the cottage will be / is fairly air tight. You should be looking at getting a stove that has an external air input so that you are not drawing combustion air from the house / room. A room sealed stove would be better (a step further than external air input) Installation of the air duct to the stove could be 'interesting' depending upon the construction of the wall. (I have experience of putting ducting in a 80cm stone / rubble wall, once was enough) Also given that you have a thatched roof you should probably get a spark arrestor on the chimney and discuss the installation of a wood burner with your house insurance provider before you purchase the wood burner as they may have a view on wood burners and thatched roofs which may involve anything from an increased premium on the fire risk to an exclusion of cover for a thatch fire caused by sparks from the chimney or a chimney fire. It would be best to know before you get the wood burner.

Re MVHR If the roof space is confined then try to get a unit that can be serviced from below so that maintenance can be done from a hatch in the ceiling without needing access to the loft.

Posted By: fostertomIn my thatched farmhouse (rented), wind blows freely thro the roof spaces, so 'thatch as insulator' doesn't have any effect. The roof space is far more open-air than any slated or tiled roof. Just saying.

Our neighbour has a thatched roof, which is in need of replacement soon, and I was wondering idly what the regs are these days? Is it a 'thermal element' (or whatever it's called) so when it is replaced it will have to be brought up to current regs, which as I understand it will include fireproof sheeting underneath and some more insulation?

Thx for all you helpful comments

I have just been in Pakistan, where there is no way to escape the smokey smog, day and night. If you turn on your extractor fan, smoke comes in under the door. They claim the smog comes from India (or course) although apparently the farmers are burning rice chaff and straw about now. Fortunately W Berkshire is a little cleaner. Traffic fumes feel worse than wood smoke to me, but both are horrible. I used to bicycle in London and now I have a persistent cough which I put down to traffic fumes.

Anyway we are in the country, so I don't feel our smoke is too harmful. Caring for the environment is complicated, and the considerations in cities are very different from country. I doubt much of our smoke gets to the Greenland Ice Sheet where it might decrease albedo and help to melt the ice.

I agree the wind blows through thatch, but our thermal calculations guy did include it in his numbers. This is probably fair, because it is quite warm in our loft when the wind is NOT blowing. Our cottage is MUCH better insulated than it was when we bought it because we have blocked up the large gaps at the eaves which seems to be the traditional design. The only insulation then was a single layer of plaster. We have put planks over the gaps at the eaves and filled the space between plaster and thatch with bit of glass fibre and vermiculite, to improve fire protection.

Does anyone think a Clearview stove is better than the others?

Thx to all

Perhaps consider individual heat recovery units in the humid areas? Minimal or no ducting.

If you're set on a wood stove definitely get one that accepts an external air supply (effectively room sealed when door is shut) and also that it is approved for smokeless zones, as these are less polluting. Accept that it will be most efficient burning at full tilt so only get a small one!

https://www.hetas.co.uk/consumer/hetas-advice/smoke-control-areas/

FWIW I don't think Clearview is necessarily better.

https://www.planningportal.co.uk/info/200135/approved_documents/72/part_j_-_combustion_appliances_and_fuel_storage_systems

Insurance might be tricky al la thatched roof and wood burning stove, check it out.

Our insurance requires 2 sweeps a year to comply and we're slate.

Clearview stove provides all our winter heating, good quality.

Burning logs better than burning LPG!

Posted By: bhommelsAlthough nice in some respects, a wood burner is neither "green" nor "clean".

but sometimes the only affordable option

Posted By: bhommels

Although nice in some respects, a wood burner is neither "green" nor "clean".

Totally agree but we dont have mains gas and the woodburner seemed the best choice at the time as we have a supply of free logs and space to season them:)

A question regarding stove emissions. I understand that the sub PM2.5 are more dangerous than the visible smoke but does an older stove producing more visible smoke produce less sub PM2.5 or do the older stoves produce the same amount of sub PM2.5 per kg. of wood as a modern stove and more smoke as well?

My thoughts being if combustion is less complete would this mean that the PM2.5 are still tied up in the larger particles and those larger particles are not broken down to the point where they become more dangerous.

That abstract is pretty clear. It also points to stuff lower that PM2.5

So PinH is correct there is more or even the same PM 2.5 in a high efficiency stove
What about PM 1.0 and below, how many of these are generated ?

With the recent discussion on gas hobs versus induction hobs on the "air condition should it be banned " thread. I researched/googled a bit more and was shocked to find a lot of sub PM 2.5 on gas combustion. A lot of it is volatile say 70% but it all was implicated in health issues in studies in Canada. Must go back on the thread and state my next hob will not be gas.
My conclusion was ... better not burning anything especially inside. A lot more research needed on health effects of these very fine particles.
Does anyone know much about these ?

For example of risks of very small particles. So small they go into lungs and tissue easily. Hang around for a very long time, unlike heavier soot type particles which settle.
https://www.theguardian.com/environment/2019/nov/13/air-pollution-particles-linked-to-brain-cancer-in-new-research
Page 1 of this says natural gas is main source of PM 0.1 in area of California big cities from industrial and power generation.
https://www.atmos-chem-phys-discuss.net/acp-2018-832/acp-2018-832.pdf
My conclusion was ... better not burning anything especially inside. A lot more research needed on health effects of these very fine particles.
It is likely small particles are worse than large for health effects due to large surface area and reactivity of pollutants per unit mass
Page 31 of this seems to imply gas is a low emitter but it is inside your house, I would vent outside (2010 paper)
https://www.cewep.eu/wp-content/uploads/2017/10/905_emissioni_di_polveri_fini_e_ultrafini_english_2012-04-16.pdf

Posted By: bhommelsSo after we have ditched our diesels, swapped our gas hobs for induction, are toasters next?

No - it's going to be the electrosmog from the induction hobs

whoops repeat posted somehow

There was a feature in a quite well known interiors blog yesterday showing a property in London that had a Clearview stove installed. On prompting by a reader the editor remove the words 'clean burning'. The owner's quote was that the stove was installed because 'you have to have something to stare at'.....