A question on stoves & flues...

Bobbiblu

If anyone knows a good answer to this dilemma it will stop lots of 'differences of opinion' in my house so all replies gratefully accepted.
Now to the dilemma.

I would like a wood burning stove (have Tonwerk in mind at the mo just awaiting a price) with an insulated flue and an external air supply to provide space heating - it'll be in the middle of an open plan kitchen, living, dining area.

OH is not convinced as he thinks putting a flue out through the roof will possibly be to the detriment of our thermal envelope and airtightness and to be fair I don't know that it won't so that's why I'm asking you knowledgeable peeps and he reckons it's totally inefficient to have most of our heat disappearing up the chimney instead of heating the space...(which I agree with in principal of course, but I'm not convince this will happen, especially with a tonwerk - but I need backup from you guys )

Our new build will not be to passive standards because our budget isn't but to give you all an outline it's got all the things it should have to make it as low energy as possible...it's a simple rectangular shape, directly south facing with all the living space and majority of glazing on that elevation also, it'll be timber frame construction with high level insulation, 1.5 story, 2800sq ft, with solar panels, HRV, high quality glazing and it will be airtight.

Think that's about it for now. I have another question but I'll do it in another thread cos this is already a bit of a rant.

Cheers!

Leadership

To maintain Airtightness you will need a room sealed stove. These are a bit more expensive (I am putting two of them in in my build ).

Bobbiblu

Leadership wrote: »

To maintain Airtightness you will need a room sealed stove. These are a bit more expensive (I am putting two of them in in my build ).

Thanks Leadership, is that the same as one that needs an external air intake? (I realise now I said air supply above but I meant intake) or are you talking about something different?
Do you mind me asking you what models you're going for ? pm me please if that's a problem to say here.
Do you have any issue with fitting a sealed chimney system then or a flue? or how are you going about it?

Cheers for the reply

JuniorB

Bobbiblu - all room sealed stoves need an external air supply.
However not all stoves with external air supply are room sealed. Some of them take secondary air etc from the room.
So when talking to suppliers ensure that you ask them if their stove is 'room sealed' - some of them hardly know the difference and assume all external air supply stoves are HRV compatible. I have learnt this the hard way.

I haven't a clue about flues !! Best of luck with the build.

Bobbiblu

JuniorB wrote: »

Bobbiblu - all room sealed stoves need an external air supply.
However not all stoves with external air supply are room sealed. Some of them take secondary air etc from the room.
So when talking to suppliers ensure that you ask them if their stove is 'room sealed' - some of them hardly know the difference and assume all external air supply stoves are HRV compatible. I have learnt this the hard way.

I haven't a clue about flues !! Best of luck with the build.

Junior B,

thanks for the great info - I reckoned room sealed stoves needed an external air supply alright but like many of the suppliers I assumed all external air supply stoves are HRV compatible so very valuable point there! thanks for the reply.

We're in the same boat so about the flues but I'll plod on ...

tails_naf

Hi All,

I was wondering if anyone could offer advice on how to get a 'real fireplace' installed in a house that is airtight?

We only want the fireplace for aesthetic reasons, and are not concerned about it heating the rooms, etc, but we don't want it to make our airtightness/HRV useless when it's not in use.

What we have:
standard chimney, with separate air supply to the chimney from the outside.
chimney was built to take a standard fireplace, but is not plastered yet, so re-work could be done on it if necessary

What are our options? My guesses:
1) use the chimney closer things - and some other valve/grate on the outside air supply?
2) use a sealed firepace - I think these are common in other countries - does anyone have any experience with these?

any advice is much appreciated!

imitation

As stated above, you`ll need an air tight stove for a home with HRV, otherwise you`ll wreck your airtightness and possibly create a risk of nasty stuff like drawing Carbon monoxide out of the stove.

I`ve done a fair bit of hunting around to find an airtight stove, there are plenty of people who will sell you a stove with an external air intake, but unfortuntely most of them seem to be chancers who dont really know about room sealed stove. You can tell they are chancers if they are trying to flog you a stove with clearly has room air intake vents on the front of it, I`ve seen it a few times !

Air tight stoves are very efficent compared to open fires as far as I have gathered, like 85% efficent, I wouldnt use them as my main heating, but each to there own I guess.

I`m not too sure about the flues, I believe they should be sealed, a good stove distruibuter should be able to fill you in.

soldsold

Hi Bobbiblu,

Discussion recently on constructireland forum that gave a list of room sealed stoves - http://constructireland.ie/vb/showthread.php?t=372

Also, I have noticed that most low energy houses seem to use inset stoves (at least the ones I have seen did) which give a much higher percentage of the total heat output to the radiators and very little to the room. Possibly the lower surface area of the stove in the room keeps the heat output down but thats just a wild guess. Ive been in a number of houses where the stove cant be used without roasting the room, even with standard insulation levels. Add airtightness and twice the insulation along with elimination of cold bridges and it seems logical the problem would be much worse - but an inset stove seems to fix these issues, if you like the look of them, or can live without the traditional look of the standalone stove.

(the) stoves online ((co)(mpany that are in the) uk (if you get my drift without giving their name) list inset stoves with back boilers and external air inlets, one is the woodfire but there are probably more. Very low output to the room (2 to 4kw) and able to heat 12 radiators through the back boilers (they claim).

S

Leadership

You make a valid point about the output. My two stoves one is a inset (Fondis F50) and the other is a stove with a back boiler (Wodtka momo) so both of them have limited output to the room.

BTW I have a HRV inlet above the stove, I dont know if this helps the spread of heat around the house or not.

tails_naf

Thanks for the construct ireland link - good info, but one post there made me want to re-think the whole thing completely and rip out my HRV! It was very 'negative' on the whole idea of combining a stove/insert and HRV.

It seems what I'm looking for is a bit niche - I don't want a back boiler, or huge heat output, simply something that looks close to a real fire (can fit in a fireplace with ~traditional style mantle), but won't compromise my HRV.

I suppose a sealed stove insert is my best bet. If anyone knows one that might suit, please PM or post here.

exaisle

Ive been considering installing a small (1.5kw-5kw) inset stove in my house which has a HRV. I contacted the suppliers of the HRV and they said that the general rule of thumb was that if the stove's gross output was less than 5kw then an external air supply and an air-sealed system wasn't necessary.
HRV's tend to run slightly negative (ie, they take every so slightly more air out of a house than they put in) so using a non-air-sealed stove would only increase the "negativity" slightly.

However, they suggested contacting the stove manufacturers to ascertain how much air the stove was likely to use when fully lit and then revert to them so they could do some sums and give a more considered response.

If they are correct, I'll save myself a tide few bob by not installing an external air source.

Comments anybody? Especially dissenters! :-)

sas

exaisle wrote: »

Ive been considering installing a small (1.5kw-5kw) inset stove in my house which has a HRV. I contacted the suppliers of the HRV and they said that the general rule of thumb was that if the stove's gross output was less than 5kw then an external air supply and an air-sealed system wasn't necessary.
HRV's tend to run slightly negative (ie, they take every so slightly more air out of a house than they put in) so using a non-air-sealed stove would only increase the "negativity" slightly.

This sounds like complete nonsense to me.

The airtightness of a stove affects the performance of the house when its not lit also so the size\output of the stove is irrelevant.

If you use a non-air-sealed stove in a negative pressurised house there is a good chance that fumes from the stove will be drawn into the room by the HRV.

Your HRV supplier seems to be under the impression that air can only travel in 1 direction in a chimney i.e. from inside to outside

I'm open to correction here but this is how I understand it.

Leadership

exaisle wrote: »

HRV's tend to run slightly negative (ie, they take every so slightly more air out of a house than they put in) so using a non-air-sealed stove would only increase the "negativity" slightly.

HRV should run at a possitive pressure other wise you will "suck" in all the polutants that are one of the possitives of having the system.

tails_naf

Leadership wrote: »

HRV should run at a possitive pressure other wise you will "suck" in all the polutants that are one of the possitives of having the system.

This sounds like a very good idea. Of course I'm no expert (far from it, just getting to grips with the whole air-tight idea and its consequences), but from what I've read its important to keep HRV balanced, but keeping the intake volume slightly higher than the output volume sounds like the safest option. The LAST thing we want to do is inadvertently draw air out of combustion sources, sealed or not!

does anyone have any downsides to having positive pressure with HRV? How positive should it be - so as to reduce the likelihood of needing the system re-balanced at a later date?

MicktheMan

Anyone installing hrv in combination with a solid fuel appliance ought to consider the following:

The hrv fans (supply and extract) have a finite life. They will fail at some point. If the supply fan fails while solid fuel appliance is burning, the house will be under negative pressure and draw air into the building from fabric airtight weaknesses. One of these will be the solid fuel aplliance door (no matter how well sealed - remember this could happen years after installation and door seals could well be worn/damaged). CO (carbon monoxide) is deadly and will kill you very quickly. It is therefore vital that a good CO monitor is installed and preferably linked to the hrv unit to kill power if alarm is triggered.

tails_naf

Good point. I was planning on installed a few CO detectors anyway - but it would be a good thing for the HRV units themselves to build in CO detectors.

I suppose building/safety regs are probably a bit behind the times, but I would imagine in future it being a requirement to be able to shut down the HRV in the case of either CO detection, as well as a fire alarm going off - as I imagine it would also be bad to be blowing air into a burning house.

Installing some control like this means hooking up the co detector/fire alarm to a relay to cut the HRV power - there could be a neat niche business here sorting this kind of thing out for new builds, as clearly the HRV suppliers and manufacturers themselves don't seem to be doing it currently.

exaisle

exaisle wrote: »

Ive been considering installing a small (1.5kw-5kw) inset stove in my house which has a HRV. I contacted the suppliers of the HRV and they said that the general rule of thumb was that if the stove's gross output was less than 5kw then an external air supply and an air-sealed system wasn't necessary.
HRV's tend to run slightly negative (ie, they take every so slightly more air out of a house than they put in) so using a non-air-sealed stove would only increase the "negativity" slightly.

However, they suggested contacting the stove manufacturers to ascertain how much air the stove was likely to use when fully lit and then revert to them so they could do some sums and give a more considered response.

If they are correct, I'll save myself a tide few bob by not installing an external air source.

Comments anybody? Especially dissenters! :-)

Well, that certainly worked! I'm sending the replies to the HRV and stove manufacturers.....thanks everybody!

exaisle

OK...so I got the negative/positive side of things a**e-ways....

Next question...can anybody suggest an air-sealed insert stove that will fit in a standard fireplace? The one I'd had my eye on, the Clearview Vision doesnt have the facility to use an external air source.....

The external air source isnt a huge problem as the fireplace effectively backs on to an external wall.

E.

JuniorB

Quick Q on stoves. I'm looking at a model that gathers hot air above it and this can be distributed into other areas via vents. The supplier is telling me that I cannot use my HRV system but have to put in seperate ducting. What is the reason for this?
If I can't do it this way I assume I can have a HRV inlet close to where I have one of these vents to suck up the hot air and distribute it around a bit?

sas

exaisle wrote: »

OK...so I got the negative/positive side of things a**e-ways....

So you described positive but called it negative? This is just for my own knowledge as I'm familiar with the technical terminology on that topic.

exaisle wrote: »

Next question...can anybody suggest an air-sealed insert stove that will fit in a standard fireplace? The one I'd had my eye on, the Clearview Vision doesnt have the facility to use an external air source.....
E.

WHen you say a standard fireplace, do you mean the standard opening with a concrete fireback?

exaisle

sas wrote: »

So you described positive but called it negative? This is just for my own knowledge as I'm familiar with the technical terminology on that topic.

Erm...no. I described negative pressure and called it that....
Pumping slightly more air into a space than you take out will result in marginally higher air pressure within the space(ie. house)., ie. positive air presssure.

The disadvantages are that you risk pumping warm and possibly humid air into walls and insulation and risk rot and mildew if the house isn't exceptionally airtight.

This explains it better than I can:
http://www.indoorairquality.net/Venmar/how.htm#The%20Impact%20of%20Negative%20or%20Positive%20Indoor%20Air%20Pressure

To answer your second question...yes, a standard opening with a concrete fireback.

E.

exaisle

@JuniorB: You need to use a room-sealed stove....one that takes air from outside and supplies it to the stove...and doesnt affect the HRV system. (if you dont, you will be sucking air out of the room and may end up sucking cold air from outside which kinda defeats the purpose of the HRV in the first place).

Now you're down at the same level as me.....staring wide eyed in the headlights..... :-)

E.

Bobbiblu

Hi Guys, thanks for all the input and for that very informative link soldsold. I've read through everything and had a good think about it and what I've come up with (though it may change) is I'm not going to install a stove at all.

After reading all the scenarios about stoves and HRV systems and considering we wouldn't use it as a main heat source & will only light it for aesthetic reasons anyway (like we do with the fire in our current house) I don't really think I can justify the additional expense....not to mention the potential hassle!
The plan now is to use the money that would have been spent on the stove on improving the fabric of the build envelope thus minimising the need for heat in the first place and then...buy lots of candles

That's the plan but like I said it's subject to change. Thanks for all the discussion. It's been a real help in arriving at my decision.

Leadership

Thats the best option all round Shame my partner would not listen to reason.

Maybe have a look at a ethanol fire if you want the looks of the fire. These need no flues or anything.

exaisle

@ Bobbiblu : Your SO will start whinging about the lack of a fire within a month of you moving in....I guarantee it....I was that soldier! ;-)

Id suggest a life-sized picture of a stove...or one of the mock-fire things you used to see on two-bar electric heaters long ago with a metal cap that rotated giving the impression of a lit fire (badly!).....or a flat screen tv with a repeating movie of a nice log fire.....

I'll remove my tongue from my cheek now :-)

exaisle

OK...to answer my own question....air-sealed insert stoves that fit in a "traditional fireplace" (ie. a standard opening).....which in my case is 760x460x330(HxWxD in mm) Thats about 30"x18"x13" in old money.

Nestor Martin IN13 - not yet available but will be before winter...I am assured that this will fit without the need to engage in major (re)construction work. I'll be watching this space carefully.

Any of the other insert stoves I've seen require either additional height or, in most cases width. If anybody knows of any other inset stove that will fit in the above dimensions, then let me know.

Plan B - find a free-standing or wall-mounted stove which is air-sealed (has its own external air supply specifically for houses with mechanical heat recovery systems...

The major difficulty here is the height of the existing opening. Given that the height of the existing opening is 760mm from the floor, one needs to find a stove that has the top of its flue opening no higher than about 750mm from the floor...in order to let the flue exit to the rear and then up a 90degree bend and up the chimney.

Most of the available stoves look like "traditional stoves"...such as the Nestor Martin S13, S23 etc or the Clearview range. However, there are also some modern looking stoves available like the Hwam Vivaldi, 3310,3320 or 4410 (very cool looking but relatively expensive...).

If anybody has any more information on this, please post it.

Finally, I'm open to correction on any of the above! Feel free to post here or PM me and I'll be happy to amend as necessary!

E.

paddy147

Just to give a few of you some inspiration.

From this crock of a horrible 1970s open fireplace,to this modern Riva 66 8kw cassette/built in multi fuel stove.

I know which I like best.:D

sas

paddy147 wrote: »

Just to give a few of you some inspiration.

From this crock of a horrible 1970s open fireplace,to this modern Riva 66 8kw cassette/built in multi fuel stove.

I know which I like best.:D

Lovely job Paddy, BIG improvement.

paddy147

sas wrote: »

Lovely job Paddy, BIG improvement.

Most important opinion,was the girlfriends 1.

Ones she approves,than thats fine with me.:D

Thanks.:)

bakerbhoy

Bobbiblu wrote: »

Hi Guys, thanks for all the input and for that very informative link soldsold. I've read through everything and had a good think about it and what I've come up with (though it may change) is I'm not going to install a stove at all.

After reading all the scenarios about stoves and HRV systems and considering we wouldn't use it as a main heat source & will only light it for aesthetic reasons anyway (like we do with the fire in our current house) I don't really think I can justify the additional expense....not to mention the potential hassle!
The plan now is to use the money that would have been spent on the stove on improving the fabric of the build envelope thus minimising the need for heat in the first place and then...buy lots of candles

That's the plan but like I said it's subject to change. Thanks for all the discussion. It's been a real help in arriving at my decision.

Bobbiblu
We installed a tonwerk last November and are delighted with it , we also have hrv.It is a storage stove so is very efficient and gives out heat for hours after the fire has burnt out .It is a pricey item but it's not an ornament.
You will probably spend more on floors/doors etc for looks


https://us.v-cdn.net/6034073/uploads/attachments/90685/105465.JPG
https://us.v-cdn.net/6034073/uploads/attachments/90685/105466.JPG

exaisle

paddy147 wrote: »

Just to give a few of you some inspiration.

From this crock of a horrible 1970s open fireplace,to this modern Riva 66 8kw cassette/built in multi fuel stove.

I know which I like best.:D

Lovely Job, Paddy!

I think the Riva 40 would fit, but there doesnt seem to be an external air kit available.....