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Room Sealed vs External Air Supply

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  • 16-09-2010 4:15pm
    #1
    tails_naf
    Registered Users Posts: 861 ✭✭✭


    I've heard that a stove having 'an external air supply' is not the same as having a room sealed stove.

    I'd imagine that if a stove was taking it's air from outside,then the combustion would not draw any air from the room - so would this suit MHRV then? What 'extra' does room sealed do?


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    #2
    tails_naf
    Registered Users Posts: 861 ✭✭✭tails_naf


    I'm resurrecting this thread as I still am unable to figure this one out.

    I've called countless showrooms for stoves and stove manufacturers, and none of them seem very familiar with the whole 'airtight and MHRV' idea (even though new building regs will make all new houses pretty much require MHRV, or so I hear).

    I see a lot of nice stoves that have external air supplies, but if I ask resellers, they seem unable to say for sure if it is room sealed or not.

    So my question is - if a stove takes an external air supply, can it be used with MHRV?

    I have my eye on stoves from a manufacturer in Ireland, and they do have external air supplies, but I just want to know if it will do or not.


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    #3
    coillsaille
    Registered Users Posts: 526 ✭✭✭coillsaille


    +1

    I am also scratching my head about the answer to this one. Any clarification would be just great!


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    #4
    sas
    Registered Users Posts: 1,282 ✭✭✭sas


    The conclusion I've come to and I'm opento correction....

    Room sealed means that the unit is specifically designed for airtight homes and the only possible source of combustion air is the external air supply.

    The non room sealed with external air supply still have the traditional vents on the front for drawing from the room. These may be closable but won't always be fully sealed when closed. I also believe in some cases it's opportunistic manufacturers trying to get into a market without actually creating a product for that market i.e. take existing stove, add air supply to it, market for airtight home.

    A familly member recently asked the local waterford crowds main agent about external air supplies. He contacted them and they said they'd never heard of it. The agent then came out with this beauty "Well, if waterfordcompanyname don't do it, it's clearly not the way to go". Fantastic!

    Note: In reality there is no such thing as a fully room sealed stove. The passive house institute are adamant about this. In my case I've to stick a damper on the air intake and in the chimney as it passes through the insulation layer to help reduce draft further. This has been a complete balls to accomadate and I recommend anyone run a mile from trying to do something like this.


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    #5
    heinbloed
    Registered Users Posts: 1,632 ✭✭✭heinbloed


    The OP asks:
    So my question is - if a stove takes an external air supply, can it be used with MHRV?

    All combustions must be able to run safely, with or without other MHRV.

    A pressure differential is required to guarantee that.
    This means if the airflow is interfered with ( the min. negative / positive pressure differential necessesary to guarantee a safe combustion = the smoke going up the chimney !) the ventilation system switches off.

    These pressure differential guards are a vital safety equipment.


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    #6
    tails_naf
    Registered Users Posts: 861 ✭✭✭tails_naf


    heinbloed wrote: »
    The OP asks:



    All combustions must be able to run safely, with or without other MHRV.

    A pressure differential is required to guarantee that.
    This means if the airflow is interfered with ( the min. negative / positive pressure differential necessesary to guarantee a safe combustion = the smoke going up the chimney !) the ventilation system switches off.

    These pressure differential guards are a vital safety equipment.

    This is the first I've heard of pressure differential guards. Are you saying this is built in to MHRV units, or is some external equipment that must be added to the system?

    Also, with regard to the stoves, I came accross this link which seems to suggest that external air supply == room-sealed, but from what posters say above, this is not really the case.

    In fact, it seems the vast majority of stove resellers don't get the air-tight concept! kind of crazy that people selling them are unaware of this, imho.

    I was talking to an MHRV supplier to ask if they could recommend a stove supplier, and they said that in many houses they fit MHRV, they saw xxxx brand, so I called the manufacturer of that brand, and they said they do external air, but were not familiar with the difference between that and room sealed.

    So I would hazard a guess and say there are a LOT of MHRV units installed in this country with stoves that are not room-sealed.

    I hope regs come in that cover this kind of stuff, as right now, lots of people in the MHRV business and stove business are blissfully unaware of the consequences of mismatching the two!

    I will do a little more research, but I'm guessing external-air and the fact a stove is inset (which I am looking for), may mean it will be suitable for use with MHRV. I only got a 2.8 on the door-blower test anyway, so I guess I'm not that airtight anyway!


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    #7
    heinbloed
    Registered Users Posts: 1,632 ✭✭✭heinbloed


    This is the first I've heard of pressure differential guards. Are you saying this is built in to MHRV units, or is some external equipment that must be added to the system?

    Yes. Either these pressure differential guards are part of the ventilation system or they have to be installed seperate.

    If your stove supplier can't tell you the safe minimum pressure difference (it is called greek Delta P , the units in Pascal) then you should shop somewhere else. Those type of sales people are dangerous.


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    #8
    caesarthechimp
    Closed Accounts Posts: 204 ✭✭caesarthechimp


    tails_naf wrote: »
    I came across this link which seems to suggest that external air supply == room-sealed, but from what posters say above, this is not really the case.
    External air supply is a very old concept, I have seen it in an old cottage where they had a 50mm cast iron pipe through the external wall, terminating in the back corner of the fireplace (open turf fire). The idea was always to reduce cold draughts entering the room from the hall at floor level, which would make the owners feet cold. :)
    Room sealed is one step more advanced; the air feed must be sealed to the combustion device. It came in with CH Boilers.
    Your link there does indeed show a room sealed stove with external air supply, which would work OK with MHRV. Whether this stove is actually available or is only theoretical is another matter though.


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    #9
    tails_naf
    Registered Users Posts: 861 ✭✭✭tails_naf


    heinbloed wrote: »
    Yes. Either these pressure differential guards are part of the ventilation system or they have to be installed seperate.

    If your stove supplier can't tell you the safe minimum pressure difference (it is called greek Delta P , the units in Pascal) then you should shop somewhere else. Those type of sales people are dangerous.

    What type of equipment would need to be added (i.e. whats the general name for this?). I don't believe the unit I have has it internally (but will look into it).

    If this is not a very standard feature of more MHRV units, then I'd hazard another guess that most MHRV installations do not have this pressure guards installed - because during quoting for systems and looking into it, I've not heard it mentioned, or offered once.


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    #10
    caesarthechimp
    Closed Accounts Posts: 204 ✭✭caesarthechimp


    heinbloed wrote: »
    Yes. Either these pressure differential guards are part of the ventilation system or they have to be installed seperate.

    If your stove supplier can't tell you the safe minimum pressure difference (it is called greek Delta P , the units in Pascal) then you should shop somewhere else. Those type of sales people are dangerous.
    Possibly more of an issue with gas fires and carbon monoxide?
    If a punter saw smoke coming out of the vents on a non room-sealed wood stove, wouldn't he just open a window and turn off the MHRV?


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    #11
    tails_naf
    Registered Users Posts: 861 ✭✭✭tails_naf


    Enrate wrote: »
    Possibly more of an issue with gas fires and carbon monoxide?
    If a punter saw smoke coming out of the vents on a non room-sealed wood stove, wouldn't he just open a window and turn off the MHRV?

    I was already considering adding CO alarms to each room with a stove + kitchen, and wiring these into the central fire-alarm.
    The central fire alarm will be setup to cut power to the MHRV anyway in the event of a fire, so now it will do it if either fire or CO is detected.

    Shame no one seems to make a fire alarm + CO alarm 'all in one' - so I'll have to have 2 separate alarms per room, not the best aesthetically.


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    #12
    imitation
    Registered Users Posts: 1,815 ✭✭✭imitation


    sas wrote: »
    Room sealed means that the unit is specifically designed for airtight homes and the only possible source of combustion air is the external air supply.

    The non room sealed with external air supply still have the traditional vents on the front for drawing from the room. These may be closable but won't always be fully sealed when closed. I also believe in some cases it's opportunistic manufacturers trying to get into a market without actually creating a product for that market i.e. take existing stove, add air supply to it, market for airtight home.

    Thats my take on it too, and the way it has been explained to me by a few sales people of the room sealed variety.

    Care should be taken with anything that can produce carbon monoxide, so its a really shame its such a murky issue.


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    #13
    heinbloed
    Registered Users Posts: 1,632 ✭✭✭heinbloed


    Enrate asks:
    Possibly more of an issue with gas fires and carbon monoxide?
    If a punter saw smoke coming out of the vents on a non room-sealed wood stove, wouldn't he just open a window and turn off the MHRV?

    The punter might be dead already, the house in flames. Gases like CO are explosive.

    Imagine the stove running in the living room, the punter in the kitchen frying his meal and using the kitchen extractor on full power.

    Imagine the punter now fed and tired, asleep and some air extractor still working away.
    These are forseeable risks, without a warning system such installations are simply illegal.


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    #14
    tails_naf
    Registered Users Posts: 861 ✭✭✭tails_naf


    heinbloed wrote: »
    Enrate asks:



    The punter might be dead already, the house in flames. Gases like CO are explosive.

    Imagine the stove running in the living room, the punter in the kitchen frying his meal and using the kitchen extractor on full power.

    Imagine the punter now fed and tired, asleep and some air extractor still working away.
    These are forseeable risks, without a warning system such installations are simply illegal.


    I totally agree with the risk - but if the legal situation is as you say, why has no one I've come in contact mentioned this, MHRV resellers, MHRV installers, etc? What I'd like to know is why is so little being said about this, and is it reasonable to expect that the MHRV unit has this built in? (i.e. do 99% of MHRV units sold today have it as standard?)

    Because if this is not a very standard feature of most MHRV units, then I'd say there are a large number of new irish homes at risk.


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    #15
    heinbloed
    Registered Users Posts: 1,632 ✭✭✭heinbloed


    Tails_naf asks:
    I totally agree with the risk - but if the legal situation is as you say, why has no one I've come in contact mentioned this, MHRV resellers, MHRV installers, etc?

    Have they been asked the question if the fire place/stove/combustion is safe to run with their eqipment installed ? And asked for a written guarantee?

    See, the issue is with the purchaser.

    Is it safe to handle a can of petrol next to the deep-fat frier? ... Neither those who sell petrol nor those who sell deep-fat friers are responsible when their goods are used in a dangerous way.

    Always ask for full documentation. With devices dependant on a correct air flow (stoves, ventilation ect.) the safe operation must be guaranteed within certain parameters as long as these are sold within the EU. Here the minimum pressure difference, delta P.



    The laws of physics are not known to many consumers, see-saws and water toys can teach children a lot about hydraulics. But when there is no intellectual deepening of what had been learned by experience for example by parents, school, books ect. then the laws of physics will not be used in an adults life. The average consumer simply doesn't ask for information, has not been tought that Murphy's law is a calculateable risk.

    Well, that is my answer to this question.....

    What I'd like to know is why is so little being said about this, and is it reasonable to expect that the MHRV unit has this built in? (i.e. do 99% of MHRV units sold today have it as standard?)

    You have to ask for it. If you want extras you have to ask.
    All M(HR)V systems are safe to use when you stick to the installation manual. The manufacturer simply doesn't know what funny sort of installers are using his equipment for. So he gives the safe-to-operate parameters in his manual and is safe himself.

    It is up to the operator to make sure his things are safe.


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    #16
    tails_naf
    Registered Users Posts: 861 ✭✭✭tails_naf


    First you say the average consumer doesn't ask the right questions:
    heinbloed wrote: »
    The average consumer simply doesn't ask for information, has not been tought that Murphy's law is a calculateable risk.

    And then you say the onus is on the consumer to ensure it is safe:
    heinbloed wrote: »
    You have to ask for it. If you want extras you have to ask.
    All M(HR)V systems are safe to use when you stick to the installation manual. The manufacturer simply doesn't know what funny sort of installers are using his equipment for. So he gives the safe-to-operate parameters in his manual and is safe himself.

    It is up to the operator to make sure his things are safe.

    But if I don't ask the question, or know to, how can I be expected to ensure it is safe? That is what I understand building regs are for - and my original statement was saying the regs SHOULD cover it, and the installers SHOULD be aware of it.

    In fact I would argue the onus should be on the installers. The example of a petrol can and fryer does not really apply. Stoves and MHRV systems are fixed elements of a build, that are intended for specific purposes, it is 'easy' to puts regs and standards around their use. Cans of petrol are not.

    I think MHRV installers should:
    a) be aware of stoves/combustion devices being used.
    b) be aware of pressure differential measuring devices, and install them.
    c) be aware of fire-safety aspects (i.e. don't blow fresh oxygen into a burning building!)

    And stove sellers should also be asking questions to see if the stove is suitable for the house it's going into.

    And the building regs should cover both.

    The onus should never be on the consumer in these cases, especially when the result can be death. If my house collapses on top of me due to poor supporting structures, is it my fault for not knowing all about the physics and load bearing ability of all material in my house, or is it the structural engineer's job?

    I'd be interested for others who have MHRV to comment - do you have differential pressure sensors installed - yes/no/don't know?


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    #17
    coillsaille
    Registered Users Posts: 526 ✭✭✭coillsaille


    I think MHRV installers should:
    a) be aware of stoves/combustion devices being used.
    b) be aware of pressure differential measuring devices, and install them.
    c) be aware of fire-safety aspects (i.e. don't blow fresh oxygen into a burning building!)

    And stove sellers should also be asking questions to see if the stove is suitable for the house it's going into.
    And the building regs should cover both.

    The onus should never be on the consumer in these cases, especially when the result can be death. If my house collapses on top of me due to poor supporting structures, is it my fault for not knowing all about the physics and load bearing ability of all material in my house, or is it the structural engineer's job?
    Well said! I couldn't agree more.

    The consumer who is in the middle of building a new home has a multitude of decisions to make and things to be concerned about without worrying about not receiving crucial info from the suppliers/installers just because he/she didn't know the right questions to ask.


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    #18
    heinbloed
    Registered Users Posts: 1,632 ✭✭✭heinbloed


    Thumbs up, tails_naf, we agree.

    Ask all your question at all times until they're answered and make the answers part of the installation contract. Signed and sealed. The calculation sheets refering to EN standards included. The consumer is the only controlling institution in these cases.

    Well posted !


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    #19
    BMD
    Registered Users Posts: 146 ✭✭BMD


    How can a stove be room sealed if it has a door on it? Surely the seal will be dependent on the amount of times the door is opened/closed and whether the door is correctly closed.

    Maybe I am missing something here but does the fuel on these stoves not enter via a door?

    Also, how do these room sealed stoves generally get their air if it is not through an external air kit? Is it generally via balanced flues?


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    #20
    sas
    Registered Users Posts: 1,282 ✭✭✭sas


    BMD wrote: »
    How can a stove be room sealed if it has a door on it? Surely the seal will be dependent on the amount of times the door is opened/closed and whether the door is correctly closed.

    Maybe I am missing something here but does the fuel on these stoves not enter via a door?

    Also, how do these room sealed stoves generally get their air if it is not through an external air kit? Is it generally via balanced flues?

    Room sealed refers only to where the combustion air is taken from i.e. if it's room sealed it does not draw air from the room where it is installed.

    The fuel is fed through a door as you said.

    There aren't room sealed stoves without an external air kit, or at least there shouldn't be.

    AFAIK there are no balanced flues for solid fuel appliances.


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    #21
    BMD
    Registered Users Posts: 146 ✭✭BMD


    Thanks for this.

    Can the external air be supplied via a second flue in the chimney or does it always come in from a duct behind or under the stove?

    Am I correct in thinking that the primary difference in a room sealed stove and one described as 'with external air supply' is that the one with the external air supply might also have other vents from which it draws air from the room?

    When you go to do your air pressure test, would you typically expect to see a big difference in your result when comparing a room sealed stove and one that come with an external air kit??

    Is there any measure of how well a stove is 'room sealed' to allow a comparison between one stove to another???

    Finally are there any steps you can take with a non room sealed stove to make it more air tight???

    Apologies for all the questions


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    #22
    sas
    Registered Users Posts: 1,282 ✭✭✭sas


    BMD wrote: »
    Thanks for this.

    Can the external air be supplied via a second flue in the chimney or does it always come in from a duct behind or under the stove?

    There are custom chimney systems that support this. They are damn expensive however.
    I'll pm you an example.
    BMD wrote: »
    Am I correct in thinking that the primary difference in a room sealed stove and one described as 'with external air supply' is that the one with the external air supply might also have other vents from which it draws air from the room?

    To be honest, I can't find an answer to that myself. These terms are as much marketing as technical fact.
    BMD wrote: »
    When you go to do your air pressure test, would you typically expect to see a big difference in your result when comparing a room sealed stove and one that come with an external air kit??

    Room sealed stoves do come with an external air kit. I think I get your point. The bottom line here is that as I said above, these terms are thrown around and there is no hard definition. I would expect room sealed to perform better because it's described as room sealed. Nothing else to go on.
    BMD wrote: »
    Is there any measure of how well a stove is 'room sealed' to allow a comparison between one stove to another???

    If there is I'm not aware of it.
    BMD wrote: »
    Finally are there any steps you can take with a non room sealed stove to make it more air tight???

    I assume that if there were, the manufacturers would be doing it. This isn't meant to sound like a smart answer. If the manufacturer is not happy for the unit to be made without any room vents, you really wouldn't want to go messing with it.
    BMD wrote: »
    Apologies for all the questions

    Not at all. You've just covered everything I've thought about on this topic over the last few years. It's a mine field I'm afraid!


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    #23
    heinbloed
    Registered Users Posts: 1,632 ✭✭✭heinbloed


    Well answered,sas.

    About:
    Quote:
    Originally Posted by BMD viewpost.gif
    Finally are there any steps you can take with a non room sealed stove to make it more air tight???

    I assume that if there were, the manufacturers would be doing it. This isn't meant to sound like a smart answer. If the manufacturer is not happy for the unit to be made without any room vents, you really wouldn't want to go messing with it.

    Sealing a stove will kill-off the flame. Never think about it, there would be explosive fumes created as well as CO - once it has cought fire. And hardly any heat developed from it.


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    #24
    Carlow52
    Closed Accounts Posts: 2,389 ✭✭✭Carlow52


    One issue to be aware of here is that the external air supply should not be subjected to any negative air pressure due to wind.

    The negative pressure can occur on the lee side of a house when the wind is blowing.

    In an extreme case the negative pressure can create a down draught in the chimney, especially in a 2 or 3 storey: this is why the chinmey systems that incorporate the air intake have the intake at the same position as the chimney.

    The problem can be addressed by running the air intake from both sides of the building, and take the air up from a tee


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    #25
    fclauson
    Registered Users Posts: 1,691 ✭✭✭fclauson


    heinbloed wrote: »
    ...
    .... A pressure differential is required to guarantee that.
    This means if the airflow is interfered with ( the min. negative / positive pressure differential necessesary to guarantee a safe combustion = the smoke going up the chimney !) the ventilation system switches off.

    ...

    What happens if you open a door or window - this will upset the MHRV, unbalance the airflow - and if what you are suggesting will switch the MHRV off

    is my interpritation righ here ??


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    #26
    heinbloed
    Registered Users Posts: 1,632 ✭✭✭heinbloed


    Fclausson asks:
    What happens if you open a door or window - this will upset the MHRV, unbalance the airflow - and if what you are suggesting will switch the MHRV off

    is my interpritation righ here ??

    Yes.
    The ventilation system can be switched-off by various methods, depending on the type of installation. Contact the manufacturer of your ventilation system for details.


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    #27
    fclauson
    Registered Users Posts: 1,691 ✭✭✭fclauson


    what methods for switching have you come across and what would you deem to be the best

    One that switches off everytime there is an inbalance in the system does not sound good to me - if you shut an internal door - would this not create sufficent pressure wave to turn the system off

    Also one which turns off if you open a window would also not make sense - you might need to purge ventalate a room at one end of the house while the other still needs ventaliating



    What method have you employed ??
    Does you have an alarm when it powers itself off


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    #28
    heinbloed
    Registered Users Posts: 1,632 ✭✭✭heinbloed


    @fclausson:

    Contact a civil engineer to get the basics of safety considerations explained to you. Every individual installation needs to be done to meet ALL safety criterias.
    This thread is about stoves and ventilation systems. A deadly mixture in the hand of amateurs.


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