Airtight home: Room sealed stoves?

sas

I think this would make an interesting topic.

A friend of mine is 2 years in their passive house. I can't remember what they scored on blower door but it was better than 0.6 for the PH standard.

He has a room sealed boiler stove, a model that was recommended to him by the PHI. It's a timber stove. He was an external air supply to it. This is his only source of heating and hot water.

He went through 1 heating season and noted that when the stove wasn't lit, it was noticeably cooler in that room. Also, even if the stove was still burning away when he went to bed, the stove itself would be cold the next morning.

He got it into his head that the fresh air supply was the cause of this.

So he tried an experiment.

He capped his fresh air intake pipe.

He left the hole on the back fo the stove for the fresh air intake open to the room.

He placed two CO monitors either side of the stove and he worked away as normal.

The room is now much warmer when the stove isn't lit.
The stove is always still warm the next morning when he comes down.

The stove doesn't burn as vigorously as it previously did, this he did state. It isn't however affecting it's performance in any perceptible way.

The CO monitors have never triggered. This I take as very important.

He hasn't had a problem with fumes into room etc when he opens the door to refuel.

One might suggest that room sealed stoves are somewhat of an expensive con.

Thoughts?

Frank Black

Your friend has violated the second law of thermodynamics.

The scientific community and media will want to talk to him.

sas

black francis wrote: »

Your friend has violated the second law of thermodynamics.

The scientific community and media will want to talk to him.

He doesn't live in a vacuum, it's a well sealed house, that's all.

When we did the blower door on my home we also did a smoke test. There was very very significant smoke leakage visible outside. If I hadn't already been told my result that afternoon, I'd have been panicing that our efforts had failed entirely.

I got 0.32 that day. So a very good result but still a lot of leakage.

sydthebeat

black francis wrote: »

Your friend has violated the second law of thermodynamics.

The scientific community and media will want to talk to him.

Mod warning.

If you cannot be helpful. Do not post.

If you have something significant to add, please do in a clear manner.

beyondpassive

It may be worthwhile to add a damper to the supply air. The leading German wood burning stove manufacturer has an electronic supply air damper with 5 positions to regulate the burn.

You can have a stove which uses make up air or room air with a MHRV, but you need pressure sensors in the flue to boost the MHRV when it senses a backdraft.

The backdraft damper, we've all put in the exhaust flue, dosen't really deal with the cold air cycling through the stove.

It's worth saying that Stoves are dangerous and you have to design in the external. supply air, I wouldn't advocate relying solely on the monoxide alarm.

The Parrot

this is very interesting i would have thought the roomed sealed stove would have avoided this.
umm i have to re think my stove heating ideas

sas

beyondpassive wrote: »

It may be worthwhile to add a damper to the supply air. The leading German wood burning stove manufacturer has an electronic supply air damper with 5 positions to regulate the burn.

You can have a stove which uses make up air or room air with a MHRV, but you need pressure sensors in the flue to boost the MHRV when it senses a backdraft.

The backdraft damper, we've all put in the exhaust flue, dosen't really deal with the cold air cycling through the stove.

It's worth saying that Stoves are dangerous and you have to design in the external. supply air, I wouldn't advocate relying solely on the monoxide alarm.

I should have been clearer that I'm not advocating this. I'm intrigued by it.

There are stoves that the manufacturers won't state are full room sealed. They have external air supply but can still draw something from the room. These are cheaper than the ones sold as fully sealed. Quite a but cheaper.

I have a damper for my supply air and but it will be at floor level under the stove.

sas

The Parrot wrote: »

this is very interesting i would have thought the roomed sealed stove would have avoided this.
umm i have to re think my stove heating ideas

The bottom line is that (with no dampers installed), cold air will flow through the stove up and up the chimney. It will do this 24/7.

This air flow will draw heat from the stove\flue and carry it out of the house.

The PHI recommend that when a stove is used, the flue be outside the thermal envelope to minimize this effect. Placing it outside the thermal envelope though ain't easy.

juniorballyc

It's worth saying that Stoves are dangerous and you have to design in the external. supply air, I wouldn't advocate relying solely on the monoxide alarm.[/QUOTE]

Why are stoves dangerous? Prob stupid question but getting one for our new build to heat rads.....

sydthebeat

juniorballyc wrote: »

It's worth saying that Stoves are dangerous and you have to design in the external. supply air, I wouldn't advocate relying solely on the monoxide alarm.

Why are stoves dangerous? Prob stupid question but getting one for our new build to heat rads.....[/QUOTE]

because they use up the oxygen in a room.

if the room is well sealed, and the stove doesnt have its own air supply, it could have fatal consequences on the inhabitants of the house.

fclauson

I have a room seal stove with external air supply - there is an integrated damper at the base of the stove which can close off the incoming supply somewhat but as SAS mentions the metal of the stove is definalty colder than the wall etc next to it due to the draft

manufan16

I have a room sealed stove with external air supply which can get cold too however during recent cold spell after leaving air intake adjuster on it open I noticed condensation drips - see image!

rja1871

HI Folks First post from the UK.

I am building 3 storey fairly airtight house and hoping to install woodstove on middle floor with twinwall internal chimmney 6m in length straight up. External air is my concern and if I install, do I insulate air supply in floor void to stop condensation?
What are peoples thoughts on this report,as it seems to me that the wood stove burns small quantities of air?

http://www.woodheat.org/the-outdoor-air-myth-exposed.html
Many thanks RJA1871

fclauson

manufan16 wrote: »

I have a room sealed stove with external air supply which can get cold too however during recent cold spell after leaving air intake adjuster on it open I noticed condensation drips - see image!

Do you know what the humidity in your house is sitting at ? (min is about 40% )

moby30

Would the size of a room and an open plan house have any impact if I were to seal the fresh air supply for the stove? I ask because I also noticed a huge difference in the temperature of the room when the stove was not on. I was going to get a grate made that I could open and close when not in use?

manufan16

fclauson wrote: »

Do you know what the humidity in your house is sitting at ? (min is about 40% )

I have no idea of the humidity level in my house , I just read I need a hygrometer - I might invest in one for curiosity's sake

heavydawson

manufan16 wrote: »

I have no idea of the humidity level in my house , I just read I need a hygrometer - I might invest in one for curiosity's sake

Jeez manufan, that's a pretty interesting photo. Great contribution! Just wondering what sort of ventilation you have in the house?
Generally speaking my understanding is that MHRV, DCV or alternatives would work to prevent such condensation on windows, so it stands to reason(ish), that they might assist your stove condensation also. Do you have some sort of non-permanent-hole-in-the-wall/window ventilation?

Also, out of curiosity, is the vent running under the floor for any appreciable length, or is it going out through some wall?

sas

Well I've HRV and in my utility on frosty nights I get condensation on the key barrel of the door. I dry clothes in there.

I have a HRV extract directly above the area where the clothes are dry.

heavydawson

sas wrote: »

Well I've HRV and in my utility on frosty nights I get condensation on the key barrel of the door. I dry clothes in there.

I have a HRV extract directly above the area where the clothes are dry.

Just on frosty nights sas? I wouldn't say that's too bad. And it's just a keyhole. With the condensation on the stove, you're talking about rusting on an combustion device, which sounds dangerous in the long haul no?

sas

heavydawson wrote: »

Just on frosty nights sas? I wouldn't say that's too bad. And it's just a keyhole. With the condensation on the stove, you're talking about rusting on an combustion device, which sounds dangerous in the long haul no?

Yes, only on frosty nights and only if I'm drying clothes at that time.

I'd have concerns about the damage condensation would do to a stove also but the person I based this thread on never reported this behaviour. It could be a side effect in Manu's case of the house drying out.

bakerbhoy

My stove has the air supply control integrated within the stove .It is controlled by the fire grate so as the weight of fuel decreases the air is reduced eventually closing off and the stove remains warm for hours.There is no other control of the air supply except for vermin control at supply pipe inlets and wind cowl on the chimney. I have not seen any signs of condensation around the base . I also have hrv installed in the house.

dos30

bakerbhoy wrote: »

My stove has the air supply control integrated within the stove .It is controlled by the fire grate so as the weight of fuel decreases the air is reduced eventually closing off and the stove remains warm for hours.There is no other control of the air supply except for vermin control at supply pipe inlets and wind cowl on the chimney. I have not seen any signs of condensation around the base . I also have hrv installed in the house.

What type of stove is it? I'm in the market for 2 room sealed stoves at the moment.

bakerbhoy

100_2889.JPG

100_2890.JPG

It's a Tonwerk t-eye swing . Not cheap . More a storage heater as it holds/radiates the heat for hours after the fuel is spent

manufan16

heavydawson wrote: »

Jeez manufan, that's a pretty interesting photo. Great contribution! Just wondering what sort of ventilation you have in the house?
Generally speaking my understanding is that MHRV, DCV or alternatives would work to prevent such condensation on windows, so it stands to reason(ish), that they might assist your stove condensation also. Do you have some sort of non-permanent-hole-in-the-wall/window ventilation?

Also, out of curiosity, is the vent running under the floor for any appreciable length, or is it going out through some wall?

I have a HRV unit controlling my ventilation although the unit was not installed at the time that picture was taken. The external air supply goes down through my sub floor under the foundations and back up to the path around the house.

I would consider the house to be fairly well dried out by now as UFH and stove have been on regularly since then.

heavydawson

manufan16 wrote: »

I have a HRV unit controlling my ventilation although the unit was not installed at the time that picture was taken. The external air supply goes down through my sub floor under the foundations and back up to the path around the house.

I would consider the house to be fairly well dried out by now as UFH and stove have been on regularly since then.

And has the condensation been present since the HRV was commissioned?

manufan16

heavydawson wrote: »

And has the condensation been present since the HRV was commissioned?

I have not seen condensation on the windows for a while now , even before the Hrv was on. I am moving in next week so ill have a closer eye on things then.

heavydawson

manufan16 wrote: »

I have not seen condensation on the windows for a while now , even before the Hrv was on. I am moving in next week so ill have a closer eye on things then.

I was actually talking about the stove. Any condensation there?

manufan16

heavydawson wrote: »

I was actually talking about the stove. Any condensation there?

None, I checked before work several mornings after I spotted that and although the unit can be cold at times I never seen a repeat of that level of condensation.

heavydawson

manufan16 wrote: »

None, I checked before work several mornings after I spotted that and although the unit can be cold at times I never seen a repeat of that level of condensation.

Phew. That's good to know. I've put in an underfloor air-inlet for two stoves in the house, and will be installing MHRV, so was keen to see that condensation wasn't going to be an issue.

fclauson

sas wrote: »

Well I've HRV and in my utility on frosty nights I get condensation on the key barrel of the door. I dry clothes in there.

what inside the key barrel - must be very small clothes

I have a stove and so far in 3 months I have had no issues - design is 3metre long 6 inch pipe from out side up unde stove - slopped down towards outside to allow any moisture to naturally drain back to out side.

The stove has a damper on the bottom which I close - and too date have seen no condensation

humidity sitting around 40%

manufan16

manufan16 wrote: »

I have no idea of the humidity level in my house , I just read I need a hygrometer - I might invest in one for curiosity's sake

I invested in a Therma-Hygrometer , its a neat little unit that shows temp and humidity and a coloured bar with arrow pointing to either dry/comfort /wet room conditions. £17.40 delivered to my door!

my temp is sitting at 20 in most rooms and humidity varies from 45%-52% however in the house 3 weeks now it is feeling a little dry sometimes.
Also the units display shows green as comfort zone and at 46% it is in the yellow zone. What is the recommended humidity level in a house? is 46% too low?


Any thoughts appreciated- maybe my HRV needs to be re-calibrated?

fclauson

the issue with HRV is that in the cold weather (remember you physics cold air holds less moisture) so its coming dry and being further dried as it passes through the HRV

our house is sitting at sub 40% in this cold dry weatehr - when a drop of "murk" comes through this rises to 45% ish

have house plants seems to be the answer

BryanF

manu! In the gaff fare play! As FF suggest house plants and reduce the mvhr air changes a little. Have you checked for thermal bridges? Hows the air tight membrane issue over front dr working out?

tred

manufan16 wrote: »

I invested in a Therma-Hygrometer , its a neat little unit that shows temp and humidity and a coloured bar with arrow pointing to either dry/comfort /wet room conditions. £17.40 delivered to my door!

my temp is sitting at 20 in most rooms and humidity varies from 45%-52% however in the house 3 weeks now it is feeling a little dry sometimes.
Also the units display shows green as comfort zone and at 46% it is in the yellow zone. What is the recommended humidity level in a house? is 46% too low?


Any thoughts appreciated- maybe my HRV needs to be re-calibrated?

sorry to change subject, where did u get above device..can u pm me link, apprecaite it.

manufan16

BryanF wrote: »

manu! In the gaff fare play! As FF suggest house plants and reduce the mvhr air changes a little. Have you checked for thermal bridges? Hows the air tight membrane issue over front dr working out?

Cheers Bryan, in a few weeks now, its probably earlier than we should have but we were eager to get in.
Based on comfort levels I reckon the membrane is fine but Iv have not had my final air tightness/BER to confirm just yet.

Im still working away each evening and weekend but Im on the last internal area to do which is my under stairs AV hub, once thats complete I am putting the feet up for a few weeks to enjoy it even more:D
While my feet are up Ill then update my post in the live self builds thread.

Feel free to pop in for a cup of tea if your in Dublin:)

Brave Harvey

Also the units display shows green as comfort zone and at 46% it is in the yellow zone. What is the recommended humidity level in a house? is 46% too low?

The least problems occur in the range between 35% and 55% and it is within this band that is regarded as the optimum in terms of comfort. Problems are health impairments such as respiratory diseases with low humidity and low temp, Virus from bacteria with too great a humidity. Then you have mould with high temp and high humidity.

Eoghan Barra

sas wrote: »

So he tried an experiment.

He capped his fresh air intake pipe.

He left the hole on the back fo the stove for the fresh air intake open to the room.

He placed two CO monitors either side of the stove and he worked away as normal.

The room is now much warmer when the stove isn't lit.
The stove is always still warm the next morning when he comes down.

The stove doesn't burn as vigorously as it previously did, this he did state. It isn't however affecting it's performance in any perceptible way.

The CO monitors have never triggered. This I take as very important.

He hasn't had a problem with fumes into room etc when he opens the door to refuel.

One might suggest that room sealed stoves are somewhat of an expensive con.

Thoughts?

This is a very interesting topic, but the discussion seems to have drifted away from sas' original thought-provoking comment.

Is there a consensus that what sas' friend has done is a seriously bad idea, or is it simply that nobody is willing to be seen to be looking at the possible merits of an approach that goes against the building regs?

Nobody has commented on the Canadian findings reported by Woodheat.org (raised by rja1871), which concluded that room sealed stoves are not a good idea (for reasons other than that discussed by sas).

I myself have installed a room sealed stove (Saey Gustav) in our new self-build, but haven't had enough use of it yet to be able to add much of value here (we only moved in a week ago). I would however be very interested to hear further contributions on sas' original comment if anyone has anything to say.

fclauson

I always thought the reason for external air is that in the event of the stove not drawing properly then there was a chance it would leak CO back into the room. This could happen in the fire was not creating sufficient draft and thus pulling smoke/CO up the chimney

In an airtight house this might be exacerbated because if the MHRV was not set right and the house was actually depressurised (i.e. extract set faster than supply) then the room would be at a lower pressure than the stove and thus air/CO could be drawn out of the stove - across the room and out of the MHRV.

Eoghan Barra

fclauson wrote: »

I always thought the reason for external air is that in the event of the stove not drawing properly then there was a chance it would leak CO back into the room.

That was my understanding too, but that's clearly not the experience of sas' friend, despite the fact that his house is very well sealed and has HRV.

Room sealed stoves obviously do mean a permanent current of cold air flowing through the air intake ducts, stove, and flue - dampers will only reduce this, not eliminate it.

If this (pretty serious) source of heat loss can be avoided without risk, then that would seem to be worth investigating. Perhaps one of the main problems is that, while sas' friend placed 2 carbon monoxide alarms nearby and has probably been very carefully watching how the stove behaves, others might not, with all the resulting potential health and safety issues (bearing in mind that every set up will behave differently in terms of draught etc.).

MicktheMan

fclauson wrote: »

In an airtight house this might be exacerbated because if the MHRV was not set right...

... or the supply fan fails first (one of them will eventually!)

fclauson

Eoghan Barra wrote: »

Room sealed stoves obviously do mean a permanent current of cold air flowing through the air intake ducts, stove, and flue - dampers will only reduce this, not eliminate it.

Mine is an inset Moroso stove - with a damper on the intake

Yes it s bit cold when not lit - but only a bit - if its that cold then I light it

I have seen no condensation (house is sitting at 40% humidity typically)

Brave Harvey

originally by Manufan - The external air supply goes down through my sub floor under the foundations and back up to the path around the house.

Would this detail be more efficient than straight through the external wall for the supply air?? It should should cut down on wind pressure? Or would it not effect it anyway as its the cold air drawn to the heat. That down and out under the foundation up to the path, would it benefit to be insulated?

Eoghan Barra

MicktheMan wrote: »

... or the supply fan fails first (one of them will eventually!)

Just for the sake of argument, let's pursue for a moment the following line of thought:

To achieve passive standard, a house shouldn't exceed 0.6 air changes/hour, so let's say a given house achieves 0.5, and that house is about 2000 square feet in size. 2000 X 7.9 (room height) = 15,800 cubic foot.

15,800 x 0.6 = Approx. 9,500 cubic foot air displacement / hour.

According to Woodheat.org a stove takes 10-25 cubic foot of air / minute, so let's say 25 x 60 = 1,500 cubic foot of air consumed / hour.

It would appear from this - admittedly very simplistic (and very possibly incorrect?) - calculation that the leakage in the fabric of the building would easily supply the required air in the event of a failure on the part of the HRV air intake fan?

fclauson

Eoghan Barra wrote: »

Just for the sake of argument, let's pursue for a moment the following line of thought:

To achieve passive standard, a house shouldn't exceed 0.6 air changes/hour, so let's say a given house achieves 0.5, and that house is about 2000 square feet in size. 2000 X 7.9 (room height) = 15,800 cubic foot.

15,800 x 0.6 = Approx. 9,500 cubic foot air displacement / hour.

According to Woodheat.org a stove takes 10-25 cubic foot of air / minute, so let's say 25 x 60 = 1,500 cubic foot of air consumed / hour.

It would appear from this - admittedly very simplistic (and very possibly incorrect?) - calculation that the leakage in the fabric of the building would easily supply the required air in the event of a failure on the part of the HRV air intake fan?

Yes - but the issue is if the leak works the wrong way (stove to room) then you will die - CO kills - no smell, no taste !!!!

fclauson

Brave Harvey wrote: »

Would this detail be more efficient than straight through the external wall for the supply air?? It should should cut down on wind pressure? Or would it not effect it anyway as its the cold air drawn to the heat. That down and out under the foundation up to the path, would it benefit to be insulated?

Not sure - but make sure that
a) the pipe slopes downwards towards the out side so that condensation and y any moisture flows outwards
b) that a suitable drain is in place to not allow any water flooding in via this route

Eoghan Barra

fclauson wrote: »

Yes - but the issue is if the leak works the wrong way (stove to room) then you will die - CO kills - no smell, no taste !!!!

Remember that Canadian studies found that spillage is just as likely to occur with a room sealed system as without:

"Outdoor air supplies connected directly to the stove or fireplace combustion chamber may seem like a good idea and it was once believed that a direct supply would isolate the combustion appliance from room pressure variations. However, two key findings from the research into outdoor air supplies serve as cautions against the widespread use of direct combustion air supplies.

1. Smoke leakage can occur, even when the appliance has tightly sealed doors. If an exhaust fan like a kitchen range hood depressurizes the room to a level greater than the draft produced in the chimney, combustion gases will leak from any available opening, such as gaps in gaskets and the joints between factory-built chimney sections (illustration below). Because air flows to zones of lower pressure, a tightly sealed combustion/venting system will spill a smaller volume of smoke into the room than a leakier system, but it will still leak unless it is perfectly sealed. Perfect sealing is not a realistic goal because it would be difficult to achieve at the time of construction or installation and is unlikely to be permanent.

2. Direct air supplies can reverse flow direction if the weatherhood is exposed to a negative pressure in excess of chimney draft (illustration below). Hot exhaust gas passing through a combustion air duct constitutes a potential fire hazard. The pressure effects of wind force around buildings can be far more powerful than the pressures produced by chimney draft. Chimney draft ranges from zero to about 50 Pa (0.2 in. water column) in normal residential installations, whereas high wind effects can produce pressures around houses up to 100 Pa.

Evidence of wind-induced reversals in combustion air ducts is becoming more common now that so many systems have been installed. When servicing systems with direct outdoor combustion air ducts, look for soot or staining inside the duct. If there is any evidence of reversal, disconnect the duct and plug the hole in the house envelope.

It has been suggested that a direct combustion air supply to a woodburning appliance would eliminate its air consumption impact on other chimney vented combustion equipment in the building. However, when their doors are closed, wood heating appliances exhaust comparatively little air from the dwelling. Wood stoves with gasketed doors consume in the range of 10 - 25 cubic feet per minute of air, which is a tiny amount of air, much less than an oil furnace, for example. Since the air consumption of a wood stove is so low, the risk of reversal of a ducted combustion air supply outweighs any advantage gained by bringing air from outdoors."

Despite the fact that it is enshrined in some building codes and its adherents are often vocally forceful, there is no scientific evidence to suggest that outdoor air supplies, either direct to the combustion chamber or indirect supplies to the living space, are reliable and effective remedial measures for combustion spillage from the appliance for which the supply is intended.

(http://www.woodheat.org/the-outdoor-air-myth-exposed.html)

And:

"Although the two studies were conducted by two labs with different set-ups, different protocols and different appliance types (1. factory-built, 2. masonry), they arrived at the same conclusion: The susceptibility to combustion spillage due to room depressurization is not affected in a predictable way by the presence or absence of air supplied from outdoors, whether supplied to the combustion chamber or indirectly through a supply duct terminating near the fireplace.

In both studies the reference room depressurization at which spillage was induced was 10 Pa. In 'Fireplace Air Requirements', none of the five tested fireplaces spilled at 5 Pa depressurization despite the fact that all were very different in their configurations and features, although all did have glass doors. The tests at the two depressurization levels were done with and without outdoor combustion air supplies.

Once the research findings were in and analyzed, the underlying physical process became clear: That is, air flows to a zone of lower pressure through any available opening, regardless of our wishful thinking. In retrospect, this principle appears rather obvious, although for most of us it was not until revealed in the lab."

(http://www.woodheat.org/outdoor-combustion-air-in-the-canadian-national-building-code.html)

It seems obvious that CO alarms are a must either way.

fclauson

Eoghan Barra wrote: »

It seems obvious that CO2 alarms are a must either way.

And a CO alarm (they are different types of gases)

Eoghan Barra

fclauson wrote: »

And a CO alarm (they are different types of gases)

Of course, my mistake

jakko86

Could anyone PM me details of stores or sites with choices of stoves for airtight houses??

Eoghan Barra

A question for sas, if he's reading this: do you know if your friend with the passive house is intending to keep things as they are (i.e. air intake pipe capped), or is this just a temporary experiment to satisfy his curiosity?

sas

Eoghan Barra wrote: »

A question for sas, if he's reading this: do you know if your friend with the passive house is intending to keep things as they are (i.e. air intake pipe capped), or is this just a temporary experiment to satisfy his curiosity?

He intends keeping it this way.