Make up air Strategies

[Nicholas]

New to the forum, So let Me introduce and start off on a iffy topic.
I am a lic. builder in Maryland, I do a lot of rehab work and build new construction every few years.
I overbuild most things I touch, and over think/study everything. I have a interest in building engineering and Alt. HVAC systems.

Anyhow first up.

I read the threads dealing with makeup air (Outside Air Intake) for wood/pellet burners, any good info got lost in the mountain of "legal/code" quoting. It does not matter if it is to code, if it is filling the house with smoke, I am getting a phone call.

The facts (know problems) as I have direct experiance with are:

House "A" ----
1600 sq ft., typ constuction, exterior masonry chimney, 1990 era wood burner, no ext air intake.
When The Jen Air down draft kicked on It would suck smoke out of the stove air intake (when there was a new fire)
When the stove was not in use, and there was a temp swing, the house would get a smoke "flava" to it.

House "B"----
800 sq ft , typ construction, interior S.S flue, 2001 era wood burner, no exterior air intake

The forced air furnace had a "supply hole" (4"x6") cut in the duct to put heat in the crawl, this created an unbalanced sit
in the house. The combustable air for the oil furnace was drawn from the crawl. So the furnace was pumping air out of the
house into the crawl, then the oil burner was sucking it up the furnace flue.

The owner had a good fire going and turned the furnace fan on to circulate the air in the house, about 2 hours later, it was
pulling air down the wood burners flue, filled the house with smoke.

House "C"
Home owner finished off basement, did some retro work to the duct work, it created a neg pressure in the basement, and
a pos pressure in the upstairs (basement door shut)


Bottom line -----
If the wood burners where closed systems, it would not matter how bad the home owner/builder/remodeler messed up the
HVAC system.

So what are the negatives of an OAI ? The only one I have seen is that if the whole system reverses, it "may" spit sparks out the side of Your house, Would You rather the stove spit sparks/smoke - inside the house.


With bath fans, dryers, range hoods/fans You will end up with neg. air in the house at some times.
This cannot be left up to carefull operator planning/control, IMHO a wood stove install should be designed to withstand a neg. Air situation and not fill the house with smoke.

So, New construction, You just spent 18K on sprayed in place Foam insullation, You aint cutting a hole in the wall to let cold air dump in the house.

What Do You do?

Nick

 

[elkimmeg]

New to the forum, So let Me introduce and start off on a iffy topic.
I am a lic. builder in Maryland, I do a lot of rehab work and build new construction every few years.
I overbuild most things I touch, and over think/study everything. I have a interest in building engineering and Alt. HVAC systems.

Anyhow first up.

I read the threads dealing with makeup air (Outside Air Intake) for wood/pellet burners, any good info got lost in the mountain of "legal/code" quoting. It does not matter if it is to code, if it is filling the house with smoke, I am getting a phone call.

The facts (know problems) as I have direct experiance with are:

House "A" ----
1600 sq ft., typ constuction, exterior masonry chimney, 1990 era wood burner, no ext air intake.
When The Jen Air down draft kicked on It would suck smoke out of the stove air intake (when there was a new fire)
When the stove was not in use, and there was a temp swing, the house would get a smoke "flava" to it.

House "B"----
800 sq ft , typ construction, interior S.S flue, 2001 era wood burner, no exterior air intake

The forced air furnace had a "supply hole" (4"x6") cut in the duct to put heat in the crawl, this created an unbalanced sit
in the house. The combustable air for the oil furnace was drawn from the crawl. So the furnace was pumping air out of the
house into the crawl, then the oil burner was sucking it up the furnace flue.

The owner had a good fire going and turned the furnace fan on to circulate the air in the house, about 2 hours later, it was
pulling air down the wood burners flue, filled the house with smoke.

House "C"
Home owner finished off basement, did some retro work to the duct work, it created a neg pressure in the basement, and
a pos pressure in the upstairs (basement door shut)


Bottom line -----
If the wood burners where closed systems, it would not matter how bad the home owner/builder/remodeler messed up the
HVAC system.

So what are the negatives of an OAI ? The only one I have seen is that if the whole system reverses, it "may" spit sparks out the side of Your house, Would You rather the stove spit sparks/smoke - inside the house.


With bath fans, dryers, range hoods/fans You will end up with neg. air in the house at some times.
This cannot be left up to carefull operator planning/control, IMHO a wood stove install should be designed to withstand a neg. Air situation and not fill the house with smoke.

So, New construction, You just spent 18K on sprayed in place Foam insullation, You aint cutting a hole in the wall to let cold air dump in the house.

What Do You do?

Nick

 

[elkimmeg]

New to the forum, So let Me introduce and start off on a iffy topic.
I am a lic. builder in Maryland, I do a lot of rehab work and build new construction every few years.
I overbuild most things I touch, and over think/study everything. I have a interest in building engineering and Alt. HVAC systems.

Anyhow first up.

I read the threads dealing with makeup air (Outside Air Intake) for wood/pellet burners, any good info got lost in the mountain of "legal/code" quoting. It does not matter if it is to code, if it is filling the house with smoke, I am getting a phone call.

The facts (know problems) as I have direct experiance with are:

House "A" ----
1600 sq ft., typ constuction, exterior masonry chimney, 1990 era wood burner, no ext air intake.
When The Jen Air down draft kicked on It would suck smoke out of the stove air intake (when there was a new fire)
When the stove was not in use, and there was a temp swing, the house would get a smoke "flava" to it.

House "B"----
800 sq ft , typ construction, interior S.S flue, 2001 era wood burner, no exterior air intake

The forced air furnace had a "supply hole" (4"x6") cut in the duct to put heat in the crawl, this created an unbalanced sit
in the house. The combustable air for the oil furnace was drawn from the crawl. So the furnace was pumping air out of the
house into the crawl, then the oil burner was sucking it up the furnace flue.

The owner had a good fire going and turned the furnace fan on to circulate the air in the house, about 2 hours later, it was
pulling air down the wood burners flue, filled the house with smoke.

House "C"
Home owner finished off basement, did some retro work to the duct work, it created a neg pressure in the basement, and
a pos pressure in the upstairs (basement door shut)


Bottom line -----
If the wood burners where closed systems, it would not matter how bad the home owner/builder/remodeler messed up the
HVAC system.

So what are the negatives of an OAI ? The only one I have seen is that if the whole system reverses, it "may" spit sparks out the side of Your house, Would You rather the stove spit sparks/smoke - inside the house.


With bath fans, dryers, range hoods/fans You will end up with neg. air in the house at some times.
This cannot be left up to carefull operator planning/control, IMHO a wood stove install should be designed to withstand a neg. Air situation and not fill the house with smoke.

So, New construction, You just spent 18K on sprayed in place Foam insullation, You aint cutting a hole in the wall to let cold air dump in the house.

What Do You do?

Nick

sounds to me a lot of poor planning or no pllaning was done at all. The basement retro would require outside air if the rooms are patrtitioned off and combustion air not communicating with the existing combustion heating equipment.. What wrong with a closed outside air intake to the closed combustion chamber? That way it is only drawn in as needed in a closed system whether someone spends 18k of spray foam or not.

Unless the crawl spaced were conditioned, meaning all walls insulated, there is no reason to try to heat a purely unconditioned crawlspace witha 4/6 duct oppening. That's ridic, what a waste of heat besides a direct violation to code.

What do you do? Know the dynmanics of the home. Know placement of heating vents in relationship to fuel burning allpiances. Know that separation distance may be required at the flue exits

Calculate the 50 cubic ft needed for every 1000 BTU for combustion air. Get familliar with the mechanical codes , as every issue there is addressed and could be advioded if, code was followed

Ask more questions here

 

[stoveguy2esw]

replying to the part of your question concerning possibility of reversal and pushing out sparks through the intake...
first , with a modern epa unit with an outside air intake connection. this connection is not dumping air direct path into the back of the unit. the intake coupler will connect to the draft inlet on the unit , most often (if not always) in the rear of the unit. from there the air will travel through a chamber leading to where the air is introduced to the fire (this being primary air) using one of our units as an example, others will be somewhat different but the principle holds: air comes in through the intake on the rear 3" connector to the OAK kit, from there it passes the draft control into a chamber which runs to the front of the firebox (under the firebox) it then travels up and splits into 2 passages which go around each side of the door and finally the air enters into the top of the doorway through what we call an "airwash" then through the fire. the secondary path leads up the back of the unit , splits around the firebox and enters the top of the firebox through small holes in stainless steel tubes.

for this reason sparks would be extremely unlikely to travel this distance and get out through the outside air tube, also bear this in mind , even if they could last that long , wouldnt you rather they were transited outside , than dumped out into the home?

the cases you used as examples in your post all seemed like good candidates for modern epa units with outside air connected, this will negate the "negative pressure " as well as competition for air when the second heating appliance switches on.

bottom line , locate a supplier of units which are designed to utilise OAI for any woodstove installation in houses which are insulated and sealed up this tight. there are quite many manufacturers who build this into their units now, and the percentage of units built that do not is dropping rapidly. the reason is clear. homes are built tighter, and better, when you build or refurbish a home it sounds like you put a lot of effort into this (which is good, what i would expect from a quality builder), but these issues can cause problems for homeowners who simply do not know how negative pressure works.

hope this is helpful to you, and welcome to hearth

 

[elkimmeg]

Every basement remodel requires dealing with the mechanical equipment that exist there. Proper means of combustion air must exist for all fuel fired appliances.
Many times to comply with code, an air exchange system is required. The air has to be tempered with in 20 degrees of ambient temperature the system is usually activated by a humidistat.
These codes can be found under the light and ventilation sections of codes. living space has an air exchange requirement either met by window openings or if no windows exist then by mechanical means.. Many times before I issue a permit I advise that I need combustion air requirements calculations to check that there exist enough internal volume space.
when I do my final mechanical inspections I will also address situations where the heating equipment has been installed in a boiler or confined space. You will not get occupancy till combustion air requirements are met.

 

[Nicholas]

Elk,
I am going to split this post in 2 parts
--------------------------------------------------------------------------------------------------------------------
These are where not My builds, I was called in to find the problems.

House A, all codes appeared to be followed, but the JenAir over powered a fresh fire in a cold stove.

House B, No codes, no inspections (PA) - the fix was to insulate and fully condition the crawlspace, move the OAI for the oil burner from the crawl to the ext.

House C, Harry home owner had to balance his HVAC system (this one ended in divorce)

Codes are good and all, but IMHO they are the "Lowest Common Denomonator", and the building inspectors in my area are a joke, and I am putting that nice as I can. While code violations or poor planing was the culpurt in two of the cases, not in house "A", Current codes still work on the "leaky house" theory, and it works 98% of the time. 99.9% of homes I look at have poorly designed or poorly exacuted HVAC systems, most HVAC contractors are hacks, Period.
Just look on this forum, alot of installs have smoke/smell problems.
As far as I know all modern gas/oil furnaces/water heaters are power vented and some (if not all ) have OAI for combustion. So house pressures do not afect them. The wood burner is the only one using interior air for combustion AND not power vented, a VERY BAD combo for a tight or unbalanced house.
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Lets face it ANY house can go into a severe neg pres., just to many variables. A closed wood stove install (OAI) would be unaffected (for the most part)
So who has done a OIA install ?
What has worked ?
What has NOT worked ?
Why would an OAI not work for a wood stove ?

Nick

 

[Nicholas]

Elk,just read Your 2nd reply.
I would never accept a window as ventilation, who is to say it will be open, most likley it will be closed and locked.
We allways use ERV's balanced with Mag meters.

You mentioned 50cf per 1000BTU, but if the house goes severe neg, that does nothing for You, except buy some time for the house to balance out. (like when a wife leaves a down draft on high and walks away)
If a make up air intake is tied to the furnace to temper it(the most common practice now) it will NOT provide make up air with a wood stove installation, because the furnace wil not be kicking on.

I use the code as a "base" , but they do not take into account anything outside of the norm, I think in many ways The IRC was a step back from BOCA
I have read many of Your post and RESPECT your knowlage and opinions.
I will be picking Your brain real soon about flue design


I kinda want to keep this thread to OAI for wood stoves, what works and what does not.

Nick

 

[elkimmeg]

Nick first of all you may PM me anytime and we can discuss issues..

OAk when wind hits a home the side it hits produces positive pressure the opposide side of the hone is a negative pressure location, what happens when the wind changes direction? One theory is the split the OAk to two inlet locations this would nuetralize the effects wind creates. I know some installerd that treat the outside air duct like a plumbing drain trap they will use flexible pipe and create a trap like bend this does two things eliminates any possible sparks and tow acts as a presure nuetrialzation zone.


I hear you about uneducated uninformed inspectors. Like any profession there are good ones and ones mailing it in.

 

[MountainStoveGuy]

all three of those cases seem to be qualifed for OAK. The situation A is going to be tough. Negative pressure created by mechanical exaust is hard to overcome if you cant hook up outside air to the wood appliance. A passive OAK like the condar might fix it, but it will be a point of cold entry to the living room.
I would do direct connect OAK on the ones that have a kit avalible. the only downside that i see in this situation is that if the kits are located on the leeward side of the home, it will create some negative pressure problems on the chimney system, but a hard starting stove is better then a smoky house.

 

[stoveguy2esw]

i for one have never heard of an outside air intake that detracted from unit performance when done properly. biggest keys are shorter the better , when possible they should be level with or just below firebox height,(basement installs are tough for this so compensating with a larger diameter pipe is usually necessary, and keep elbows to a minimum. (you lose up to 15% with each 90 degree elbow)