"Tight" construction and woodstoves

[Bobbin]

Our home is nearly 18 yrs. old. We had trouble with backpuffing when we first installed the Fireview in 1991. Solved it by cracking the slider on calm, overcast, "still" days. I'm now facing the same problem in my studio over the garage. Need help/thoughts on how to increase air circulation. Cracking a door/window is no big deal in our home, but I would like a more refined solution in my workroom. I don't work out there every day and wonder if there is some sort of automatic vent that will work "automatically" to equalize pressure within the building?

The studio has forced hot air heat (no water in the building), intended to maintain the temperature at 45-50 degrees and/or "take the chill off", fully programmable thermostat. Very tight construction (2007). The Woodstock "Classic" stove will occasionally backpuff (sets off smoke detector) unless a window is cracked and is left open for the duration of the burn. I can't have backpuffing since I work with fabric and can't have the smell of woodsmoke on my clients' fabrics!

Need thoughts/ideas on bringing in more oxygen for the stove/regulating the pressure within the building and how to do it while at the same time minimizing drafts amd heat loss overnight. The hearth is on the north side of the building and is raised and tiled. Cracking windows works slick but I'd rather not leave them open all night long.

 

[Hanko]

when I built my shop in 06, 1500 sq ft two story, I used dense pack foam insulation, and ony two anderson windows, i knew I would have the same issue as you. I installed the outside air kit which brings in combustion air from the out side, and have never had a negitive problem whatsoever. I have considered putting one in the house, there are times when needed although not many. There are many cheap easy ways to do it. Im sure you can figure it out.

 

[LLigetfa]

Reading the title and then reading the post reminds me of watching dubbed foreign films. The brain is trying to process what it sees of how the lips are moving but then the ears are feeding it different input. What you describe is not a "tight" house. Rather, it is a house out of balance. Warm air is escaping and not enough makeup air is getting in. Solve where the air is escaping and provide proper makeup air.

 

[Dune]

OAK seems like the ideal solution

 

[LLigetfa]

OAK seems like the ideal solution

I often advocate an OAK but it is still important to have properly balanced air in the home. In a poor draft/pressure deficit situation where the stove is not the main cause for the deficit, an OAK can actually PUSH smoke into the home.

 

[Bobbin]

I looked at some rather old newsletters sent out by Woodstock many years ago, and I know the problem is "too tight" construction (nod to LL). The recommendation was that the duct for OA run at least 8-10' from the source to the stove so really cold air was not introduced. I'm not quite sure how to pull that off, frankly (construction is not my forte, you guys). Given the 8-10' run guideline my only option is the west wall where a vent could be run between insulated floor joists. But where should the outlet be sited? remember that the hearth is raised and tiled; and how big does the intake have to be for the OAK to be effective? How big is the intake duct?

I know the problem has to be solved. And woe to me if I don't have a comprehensive plan ready to go when I ask the husband for assistance. I HAVE to have it pretty much all together and a thorough working knowledge of what has to happen and how it has to happen or it won't happen at all and I'll spend the rest of the winter opening and closing the window and making the present situation "work". I want to solve this problem one time and solve it effectively.

Thanks.

 

[LLigetfa]

I may sound like a stuck record as I repeat this in several threads, but is is all about balance. There are forces inside that must be in balance with forces outside.

Think of a hot air balloon. It stays buoyant because there are no holes up top to let out warm air despite a huge hole at the bottom. Take this principle to the building.

If the stove were the only place where air was leaving the building, there would not be enough of an imbalance to cause the symptoms described. That is why I challenge the "tight" assumption. It is tight alright, but tight in the wrong places. Somewhere, air is leaving the envelope besides at the stove and the open window is the makeup air to both the building and the stove. If air escape is reduced, so too is the need for makeup air. An OAK can balance what the stove otherwise draws out of the room but if the room is still in a pressure deficit, the OAK can actually PUSH smoke into the room because the stove is now pressurized by the external force. You need to work on both the ying and the yang.

 

[Bobbin]

That's a all well, fine, and good to say, LL. And believe me, I understand what you're saying. But throw me a bone here, dude!

I've told you that there is a forced hot air furnace (read: duct work) to provide "base" heat in the depth of winter. There is also attic space above my work room (we have a roof supported by "attic trusses") and the flourescent lighting for the studio is mounted flush with the ceiling sheetrock (there are 27 lights, about 15" wX48"l). The lighting fixtures required a gap between the fixtures and the insulation, so complete insulation covrerage has been interrupted and the cutaway portions now rest atop metal rods that keep it away from the top of the lighting fixtures. Plenty of room for air escape there, huh? There are two bays and the doors are "automatic" which implies that they are not terrifically insulated.

I'm not stupid. But like many others sometimes the view is obstructed because there are too many trees in the way. So, what you're saying, LL, is that there is so much air escaping around the ceiling mounted lighting fixtures that the stove is being deprived of the oxygen it requires to maintain a fire and vent the exhaust properly. Do I have it right?

 

[Ratman]

Easily solved by pressurising the stove room.
Pull cold air from an adjacent room or hallway into it.
Circulation will take place and can be maximized with a ceiling fan in the next room.
Set it to the winter position (clockwise) thus pushing the warm air back down along the walls as it displaces the sinking air being pulled by the other fan which is pushing cold air into the stove room.

Holy run-on sentence Batman!
This is a proven advantage.

 

[DAKSY]

So, what you're saying, LL, is that there is so much air escaping around the ceiling mounted lighting fixtures that the stove is being deprived of the oxygen it requires to maintain a fire and vent the exhaust properly. Do I have it right?

No. You do not have it right. It's not about oxygen.
It's about air pressure. There is less air pressure at your stove load door,
than there is at the top of your chimney.
Air flows from hi to lo pressure, so it's flowing down your chimney & out of your stove.
In order to bring the pressure up on the inside of
your building you have to lower what is known as the Neutral Pressure Plane (NPP).
This is where the air inside & outside are in perfect balance & if you opened a window EXACTLY on the NPP,
there would be NO movement IN or OUT of your building.
The NPP in your building is ABOVE your stove for whatever reason &
you need it to be lower.
To lower the NPP in the building, you have to seal the leakages above it.
Look at it this way: if you filled the room - where the stove is - with water
& then turned the ENTIRE room upside down, would the water stay in it?
Probably not, & the outflow spots are where you need to seal the airflow.
Recessed light fixtures & attic access trap doors are prime suspects in these situations.
HTH

 

[LLigetfa]

...the flourescent lighting for the studio is mounted flush with the ceiling sheetrock (there are 27 lights, about 15" wX48"l). The lighting fixtures required a gap between the fixtures and the insulation, so complete insulation covrerage has been interrupted and the cutaway portions now rest atop metal rods that keep it away from the top of the lighting fixtures. Plenty of room for air escape there, huh?

WOW! My guess that it wasn't a truly "tight" construction has just been confirmed. It's not about who's right, it's about understanding the dynamics of stack effect and that "balloon" won't fly.

We could spend a lot of time on should'a/would'a/could'a but that won't solve the problem. It would be a big job, but boxing in all 27 lights so that they are air tight is the best solution to the air loss. I would consider building air tight foil faced rigid foam boxes over each and every light fixture, retaining an air space within the box. An alternative might be to make airtight Tyvek covers that are sealed at the edges.

The other consideration is to bring outside air to the vicinity of the stove, not as a dedicated OAK but rather, as building air. This would take away the discomfort of cold drafts and you could add an electrically operated zone damper to it. If you wired the damper through a thermal snap switch sensor on the stove, it could be made to close when the stove is cold. You might want to have an override on it so that you could open or close it at will.

 

[Bobbin]

My workroom in on the second floor. There is no "adjacent" room, just a stair well from the first floor garage bays. My studio is 28'wX36'l and the ceiling is 8'. Fully insulated building.

With 27 cutouts in the ceiling for the recessed lighting fixtures and attic storage above my studio there is NO way I'll ever be able to plug all the leaks. I KNOW it's a building pressure problem (Woodstock literature told me that), I incorrectly used "oxygen" in my last post. So, since the stove doesn't backpuff all the time the back puffs indicate the times when negative pressure rules? when the stove can pull in no air and the resultant vacuum sucks air back down the chimney?

That said, what's my next best alternative? How do I vent the studio area effectively and is there a way to accomplish it thermostatically (read: automatically) so I don't have to continually open and close windows to accomplish the end goal?

 

[begreen]

Not to join the fray, but from the description, it doesn't sound like the studio is that tight. Is it possible that the described leakage up to the attic is creating a negative pressure zone in the room below? Also, are there any bathroom fans or other exhaust systems like a clothes dryer in the studio space? And last, does the furnace have its own OAK already?

Ideally any leakage would be fixed so that one is not heating the outdoors, but in lieu of that, perhaps the easiest way to route an outside air kit is straight down. If that puts it into the garage space. Are the joists open or enclosed? Can it be run in a garage ceiling joist space to outside or along the garaged ceiling?

 

[LLigetfa]

Since there is no access to the top of the fixtures, the only possibility is to control air leakage as much as possible at the ceiling penetration keeping building code in mind. Assuming the attic is unconditioned vented space, the air in it could be balanced in Winter to allow more cold in at the soffits and less air out up higher. If it has whilybird vents, they can suck a lot of air out of the space depressurizing it.

 

[Bobbin]

No exhaust fans of any sort. My work room is just one big space.

Clearly, the issue is "leakage" through the 27 cut outs to accomodate the flush mounted flourescent lighting. We were careful to cut the insulation bats carefully and seperate them evenly, too. We placed flexible metal rods over the bays to keep the insulation the mandated distance from the tops of the fixtures. We repositioned the remaining insulation bats over the lighting fixtures. We have done what we could to minimize heat loss with respect to insulation. Not perfect, but better than many attempts. For what it's worth the electrical contractor and the insulation people were completely unprepared for my requirements for lighting. And I was shocked that they were so unprepared.

OK, so we have too much leakage through the 27 holes in the sheetrock ceiling and that is affecting the air intake of the woodstove in my work space! Nothing can be easily done now considering the necessity of attic storage in the bahn. I will have to live with the inefficiency the recessed flourescent lighting has presented. I'm OK with that. But now I need to figure out how to give the stove what it needs to operate efficently and not impregnate fabric with the smell of wood smoke

 

[begreen]

Sounds like a stack effect is happening. For routing of an OAK, is straight down from the studio the garage? If yes, does it have a finished ceiling?

 

[LLigetfa]

If you have single wall smoke pipe, changing it out to double wall would help to keep the flue warmer and draw better. Ducting outdoor air to the stove area would provide makeup air that is less drafty than an open window. Maybe you could run an insulated duct straight down from the attic to the floor if an outside wall is too far away.

 

[LLigetfa]

Sounds like a stack effect is happening. For routing of an OAK, is straight down from the studio the garage? If yes, does it have a finished ceiling?

BeGeen,
Not sure where that line of thought is going but by code, air from a garage must not enter that space. There are also serious firestop rules to follow.

 

[Bobbin]

Yes, the studio is directly above the garage bays, and yes the ceiling is "finished". The entire building is 6" studwall construction and fully insulated. There are 2 lalley colums to support the central beam supporting the second storey. There is a truss roof with "attic storage". The stairwell leading up to the studio is fully insulated as is the door leading to it, so the studio space is effectively fully insulated., although the stairwell is chilly as there is no heat to it directly. An oil-fired furnace supplies heat to the studio area, and the thermostat is fully programmable. A divertor baffle allows redirection of heated air to warm the garage bays as desired.

 

[begreen]

read the previous post, the suggestion is to run it via the garage ceiling joist space to outside. Or along the ceiling to the outside.

 

[Bobbin]

Two flue chimney runs inside the building and meets all codes. NO problem there.

 

[LLigetfa]

If a duct runs through the garage, care must be taken not to let air from the garage contaminate the air in the duct. Also, firestop provisions and perhaps a fusible damper may be prudent or required.

I don;t believe a dedicated OAK is the answer. It would pressurize the stove and do nothing for the pressure deficit in the room. What is needed is a general makeup air vent to bring air to the space near the stove but not dedicated to combustion.

If makeup air is brought down from the attic, it could be provisioned with an inline duct blower to counter any tendency for it draft upward. The blower could be reversed in Summer to vent the space.