help sizing the external air intake

[Prometeo]

HI, another season has begun, but I've noticed migraines when I use the stove, the difference is new windows hermetic, I started investigating, and I understood that the external air intake 80 mm in diameter it's too small now, but what diameter should it have? If I partially open a window, I notice that the air enters as if it were sucked so I have internal negative pressure. I increased the hole to 100 mm diameter and now I don't have any discomfort, but the doubt is still too small. Some here recommend at least 165 cubic cm of surface area, others 250, which is very big!
An 80 mm hole would be about 50 cubic cm, while hole 100, current It's 75 cubic cm

Thanks for the help

 

[stoveliker]

First get a carbon monoxide detector (that works).
Headache is th first symptom of CO poisoning. Death is the last...

 

[stoveliker]

Second, does your stove have a possibility to connect.ti an outside air kit?
If so what cross sectional area does that have and what does the manual say about the limits to length for a certain diameter air pipe/hose?

 

[begreen]

HI, another season has begun, but I've noticed migraines when I use the stove, the difference is new windows hermetic, I started investigating, and I understood that the external air intake 80 mm in diameter it's too small now, but what diameter should it have? If I partially open a window, I notice that the air enters as if it were sucked so I have internal negative pressure. I increased the hole to 100 mm diameter and now I don't have any discomfort, but the doubt is still too small. Some here recommend at least 165 cubic cm of surface area, others 250, which is very big!
An 80 mm hole would be about 50 cubic cm, while hole 100, current It's 75 cubic cm

Thanks for the help

Does air come in at the same outside temp when the stove is not burning?
FWIW, I think 3" (80mm) is the size of the OAK. Does the ducting have a lot of 90º turns or a very long length?

A CO and CO2 detector may be in order.

 

[begreen]

Or, the stove paint may still be outgassing. If so, take the stovetop up to 600-650º for an hour to bake it in fully. Open a window while doing this.

 

[Prometeo]

Thanks @stoveliker @begreen

Basically, I always use the stove with excess air, because in the past I found carbon monoxide in the morning, closing the air excessively, in the evening,
and so now I tend to leave it very open.

On the contrary, what I noticed now,
until now, after new windows, and doors
the flame at a certain point tended to go towards the small combustion air holes,
(this perhaps indicates negative pressure?)
now that I have enlarged the air hole in the wall
it seems that the flame is freer to go,
towards the glass.

The air intake for oak is 100 mm
I have used an 80 mm duct until now,
but I have eliminated oak,
to eliminate slightly high tvocs, at times.

The manual does not indicate the maximum length of oak,
however I wonder if it is logical to think,
if the oak socket is 100
the hole in the wall 100 is good, or if it is not the same thing?

 

[Prometeo]

@stoveliker
The paint is now seasoned, I have used the stove several times even at higher temperatures.

@begreen
The hole in the wall doesn't actually communicate with the outside, but with a garage. This garage has 2 holes, each 100mm in diameter communicating with the outside.

 

[begreen]

Basically, I always use the stove with excess air, because in the past I found carbon monoxide in the morning, closing the air excessively, in the evening,
and so now I tend to leave it very open.

This sounds like a sure way to overfire the stove.

the flame at a certain point tended to go towards the small combustion air holes,
(this perhaps indicates negative pressure?)

Do you mean secondary combustion holes on the bottom of the baffle? This is the way it is supposed to work and typical of secondary combustion stoves as the primary air is reduced.

The air intake for oak is 100 mm
I have used an 80 mm duct until now,
but I have eliminated oak,
to eliminate slightly high tvocs, at times.

Sorry, I forgot you got an F500, I was thinking it was a PE stove.

Post in thread 'When to reduce air, to burn "longer"'

Mar 11, 2023

What type of stove do you have?

With my PE, I start cutting the air down to 1/2 way once the insert fan kicks on from a cold start, then shut it down slowly as the stove temps go up.

With the 13 (freestanding) , I check secondaries, and thermometer readings.

Thank you, I have a jotul f 500 has a vermiculite baffle, it has no air hoses, air comes from behind, like F400. How many degrees does your fan start?

• Prometeo

Doesn't this stove have an odd, tall flue arrangement with some backdraft issues? Or am I confusing this with a different poster?

 

[stoveliker]

The air intake for oak is 100 mm

I have used an 80 mm duct until now,
but I have eliminated oak,
to eliminate slightly high tvocs, at times.

I don't know what tvocs are. The OAK should create a system where no air interacts with the air in the room: from outside via a duct to the stove and then out the chimney. This should be the safest way to go.

The manual does not indicate the maximum length of oak,
however I wonder if it is logical to think,
if the oak socket is 100
the hole in the wall 100 is good, or if it is not the same thing?

No, if the OAK connection on the stove is 100 mm, and you add 60 meters of OAK duct, you'll not be able to suck enough air in.
So there are length limits beyond which a wider duct is needed. (Elbows etc., and corrugated duct vs smooth pipe also decrease air flow.)

 

[Prometeo]

@begreen
The chimney is 30 feet (10 meters) high to avoid overfire, I placed a slight obstruction in the oak socket, otherwise it was not governable, with this year's dry wood (2 year old hard and soft wood) I suspect negative pressure because the secondary flames, for example on the sides of the stove, come out and in the center, they almost seem to re enter into those holes. Yes, it's the F500 but last year the wood wasn't optimal, still a little damp. I just have to try to understand if, as @stoveliker indicates, oak is better (100 instead of 80) or not because the problem is the hole in the wall is about 3 feet from the floor.
Thanks

 

[Prometeo]

@stoveliker
Tvoc are volatile organic compounds


Considering that the hole in the wall is 3 feet from the floor,
is an oak plausible?
It would require 3 90 degree bends
(I couldn't make the hole lower).

Or better without oak,
and at this point the 100mm hole in the wall should be enough?

Thanks

 

[GG Woody]

It is not allowed/advised to pipe an O.A.K. up from the inlet, under some circumstances the O.A.K. could become the chimney and have you're stove running backwards. You can however pipe it close to the opening providing an air gap which I think I would recommend. 3-90° bends shouldn't be a problem.

 

[stoveliker]

Volatile organic compounds would be *less* when you have a system that's closed (from outside, through OAK duct, to. stove, through chimney to outside) than when you disconnect the OAK and have an opening (air inlet) into your room.

As said above, an OAK often can't terminate above where it enters the stove.
Some stoves (or zero clearance fireplaces) I've seen do allow this - they (I presume) have an air path in the stove that mitigates the danger.

I don't know what is best for your OAK parameters; it depends on too many things. I've seen (on this forum) OAKs of 15 ft or so, that's 5 meter.

My view is that an OAK can not often be too large; the air would just flow a bit slower in that duct. Not a problem. The only potential issue is that they can be more wind-gust sensitive if they are large. But given that this one ends in a (leaky) garage, I don't think that'll be a problem.
They can be too small.

So, if the connection on the stove is 100 mm, I'd make the duct 100 mm.
How long would the total length of the duct be?
If< 5 m, I think it'll be fine at the stove-connection-sized diameter. *Especially if you use smoothwall pipe* (rather than corrugated/flexible stuff - the undulations of the wall add a large amount of impedance to gas flow).

For both (OAK above the stove, and diameter/length issues), check your stove manual. There's a decent chance something is written in there.

 

[Prometeo]

@stoveliker
I agree but where I live I detect higher TVOCs inside the house than outside, and it's also true that if it's windy opening the door, I have a surge of these values, which doesn't happen with oak my concern, if I have smoke leak, for some reason, without oak I still have an air exchange. The oak, in this case, it would have a total length of 6 feet, 3 of which are vertical.

@GG Woody
If the oak pipe is not connected to the stove I have some doubts, I'm not sure but I think it's better not to put the tube.

It seems that an important detail, if a grill is placed in the wall hole, must be considered in the dimensioning of the diameter of the hole in the wall.

 

[begreen]

Is this the system where the stove sometimes back-drafts at the end of the fire due to the uninsulated tall chimney cooling down? If there is negative pressure in the stove room then solving the negative pressure may be more important. An oak may not be the solution.

Is there a floor above the stove room? How well sealed is the place, especially in the floor above. Are there leaky windows or vents or exhaust fans on that floor?

 

[Prometeo]

@begreen
that's right, but backdrafing it happened perhaps because the air was too closed, or because the oak went 3 feet uphill, however, leaving much open air, it hasn't happened yet. The chimney crosses 2 floors, but it is inserted in a concrete and brick wall up to the roof. The two upper floors have many drafts, old windows. I'm trying with the flip window function there is a lot of space left for the passage of air, directly near the stove, if this doesn't work either, I don't really know

 

[Prometeo]

 

[Murray01]

Do you have any other natural gas/propane appliances competing for combustion air?

 

[GG Woody]

^^^...Bath fans, range hood fan, laundry dryer, HRV...^^^

 

[Prometeo]

@Murray01 @GG Woody

there is only the kitchen extractor which could make things worse, but I'm not using. According to technical data sheets, of other cast iron stoves with 6 inch flue, I should have a hole in the wall of at least 130 mm

 

[stoveliker]

That would be surprising to me as most OAKs I see (on here) have a duct w/ smaller diameter than the flue is.

Also, this is *not* a needed hole in the wall. This is the needed OAK cross section.
You can (normally) run a stove without an OAK if your home is not too tight. Without making a hole in the wall. That is because the whole home will have gaps, cracks, seams, etc. where air leaks in, and together they have sufficient flow to make things work.

The problem is when the home is too tight (and modern homes in Europe are often too tight), and insufficient flow through such (less present) cracks exists. THen an OAK is needed, and there are generally recommended dimensions for that.

 

[Prometeo]

I think I've solved it, or on the way practically in my case, if I want to burn without oak, I have to widen the hole in the wall because I have no drafts in this basement, in the windows, doors, everything is almost airtight, practically without oak the 100 mm hole in the wall pushes air inwards heavily, a flame from a cigarette lighter, it doesn't stay lit, near that hole, this pushes me to understand that there is a strong negative pressure inside the house and therefore, to avoid widening the hole and risking remaining in negative pressure, I returned with the oak, however the oak does not have to be sealed but there must be an air passage to nullify any other negative pressure, which can be when I open the stove door or I turn on the extractor fan in the kitchen. Or seal oak but open another small hole in another place. Thank you all for your contributions, I was on the way to buy an air conditioner, but never say never!👍

 

[begreen]

The best solution is to stop the house from being a chimney. The air leaks upstairs are causing air to be sucked in downstairs. They are causing negative pressure downstairs. Making a bigger outside air hole by the stove is just treating a symptom and not fixing the problem. Fix the upstairs leaks and you probably will not need to worry about the outside air.

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[Prometeo]

@stoveliker
Exactly, my house is not modern, but being in masonry, not very insulating, and to maintain the heat we tend to seal everything, the oak is really necessary, and a precaution would be to open the window for reloads!

@begreen
It could be another reason for negative pressure, but I have a door to the stairs, I only use the stove for basement. "woodheat" seems like an interesting site, I'll take a look, wood stove is not an appliance!

 

[begreen]

@begreen
wood stove is not an appliance!

Except when the manufacturer considers it an appliance.