Negative House Pressure

[stvc]

I forgot to ask, can you inspect that radon system piping to make sure it is all intact and not depressurizing the house?

[energy_rater_La]

had you done any duct sealing between the blower door testing & today's duct blaster test?
I know you did some house leakage sealing.

even small leaks on duct system adds up. what size is the central system in your home?

and sealing the bath fans...re-visit my post on gardenweb about dropping the
cover of the bath fan and sealing the gap from inside the house with hardcast 1402
mastic tape. foam shrinks and doesn't seal as well as you think. caulk doesn't fill large
gaps & as it dries it shrinks, so if you caulked...you may need to touch it up. if you foamed
then caulk foam to sheetrock/housing of bath fan. or just mastic tape it.

I've been thinking about your bumpouts. if the building envelope was compromised
when they built these bumpouts, it will be both at the bottom of the bump out
and the top. they wouldn't have changed methods.

while opening up the cabinet bumpout is the best way to air seal it, I usually seal
from exterior and follow up with interior sealing.a secondary seal is always a good idea.
its difficult to fit a caulk gun into the
cabinet, but if you can...caulk all the joints in the wood. if you have a sink, move the
escustion and seal oversized holes there. I found a product at hvac supply that is a rope
caulk called Thumb Gum. it is a pliable material that you can use around plumbing penetrations.
I've used it with good results.
I have some cabinets with false boxing above them. I sealed from in the attic, caulked false
boxing joints & tried to caulk inside cabinets...no luck...caulk gun too big/cabinets too small.
I used hardcast mastic tape to seal the gaps. doesn't look great, but it is just storage for
all the building science books & related materials. sealed well.
just ideas on how to seal these areas for you to think about.

did you feel around return framing at attic floor? 2x framing, corners & where they rest
on each other?

what is sq ft of home & what were blower door numbers ? (not ela but 2500 cfm at 50pa
number) if you've posted this already...sorry I must have missed it.

have you been in contact with your auditor since the test?

[stvc]

From one of the first posts,

sqfeet: 4523.84
Volume: 39743.90
CFMs @ 50: 2400

Airflow building: 231.84
Airflow people: 75
BAS at CFMnat: 231.84
BAS at CFM50: 3987.64
2791.34
70% of BAS: 6

Actual
Volumes/day: 5.06
Volumes needed: 8.40

I ran the numbers to convert to ACHn and came up with something like .24 but was guessing on N factor. Still close enough for me to question it. He also has a low RH so am really thinking those numbers may be wrong.

[hearthman]

I'm questioning a lot more than just the numbers but the auditor's technique as well. Several things questionable here.

Thinking about the cold air infiltration from outlets near but not 'in' the bump out leaves me to believe there is air shunting laterally through walls. You can get air into one stud cavity then travel sideways through holes bored for wiring and pipes (which shouldn't be in exterior walls-wires ok). A lot questionable here.

I think for one they got the wrong company to do this and two, they need someone with an IR camera and some sort of smoke puffer or fog machine to find these leaks.

[taverty]

The duct blasting tech noted that since we have 9' ceilings on all three floors he thought that could be a contributing factor in raising our neutral pressure plane. He said in other homes the neutral pressure plan is probably even with the first floor, but in our house he thought it was mid way up our first floor. He said this would cause the negative draft at the downdraft and fireplace since they are both lower than the pressure plane.

Also, since the duct blaster tech was surprised to hear this I thought it may help here. My home doesn't have any house wrap, no TyVek, just brick veneer front with vinyl siding on the other three side, then under that OSB.

I don't know if it matters, but our house is actually 5,000 sqfeet. I mentioned it to the audit company but she said it just needed to be a rough estimate. I'm mentioning it now since I'm grabbing at anything!

During the blower door test it really seemed like the house was struggling for air (maybe that's how every house feels). It felt like you were in a vacuum and any door you opened to the outside you were met with a major gust! Also, my Trane propane furnace in the basement shut itself down during the test. I can only assume it was because it detected a major downdraft on the flue. The blower door tech was surprised it did that. We didn't cut the power to it before the test, we only turned it off at the thermostat. She almost stopped the test right there once she saw that. When the test ended I had to cycle the breaker for the furnace to power back up.

stvc, I'm going to have the original audit company out to do the test out. I was originally going to wait until I had the attic insulated and rim joist spray foamed but I think it may be useful to have her out now to verify the leaks I did seal. The active radon system (the orb part) was installed within the last year. I didn't notice any change from before and after it was installed. The PVC pipe has always been there, passive radon pipes are required here. I will still double check it. I can unplug it in the attic very easily. However, I'm not sure how I can check the PVC pipe itself (buried in interior walls). I assume I'd have marks from water on my walls if there were any breaks. Also what is the N factor? Is this something I can ping my auditor on and get an accurate value?

energy_rater_la, I definitely plan on following all of your sealing advice from GardenWeb. It's my easter weekend project, much to my wife's chagrin! Yeah, I have to seal all the pipe penetrations under the kitchen sink, which does sit in the bump out. I'll try the Tumb Gum, if there's one thing I've learned it's that I really dislike expanding foam!! I haven't really been in contact with my auditor since. She offers a test out, which I was going to take advantage of, I really wanted to do it at the very end. But at this point I should have her out again. My downstairs unit is a 3.5 ton A/C 100BTU furnace (80% efficient). My upstairs is a 2.5 ton heat pump, not sure of the electric coil BTUs. When they come on though it's nice and toasty, but all I see is dollar signs!!!

Thanks again!

[taverty]

heartman, I didn't see your post when responding above. What you're saying makes sense. At this point I think I need to bite the bullet and have another audit company out. I was trying to avoid it since it's ~$500 for another company. She did have an IR camera during the test. I saw all the blue areas around the fireplace and kitchen bump outs and a lot of the exterior outlets. I also saw the blue creeping down the outside walls on the second floor. That's when she said my top plates were leaky. I think you're right that a smoke machine would help.

It's strange because even with the duct system being so tight, I still have those drafts. The duct blasting tech really wasn't sure why. He thought it was convection, my returns are only R-6.

[hearthman]

They should not have been running the test with an atmospherically vented furnace running. That could put you at risk of CO exposure and they should know better.

They should have taken a baseline for the Stack Effect With Respect To (WRT) outdoors. With 3 stories, yes, you can have significant stack effect alone in such a voluminous house. As the warm air rises, it creates a suction below. If there are upper level leaks or exfiltration, this gets exacerbated. You could install a makeup air (MUA) system that basically controls where the leaks are below the NPP and how much but it will add to the CFM 50. For the furnace to kick out on pressure switch, there has to be significant depressurization. Did they conduct a Worst Case Depressurization Test and if so, what was the result? If your furnace is a two pipe high efficiency unit the test should have no effect. Should... The tech should have been monitoring for backdrafting with a CO analyzer btw even with pilots at standby or the furnace off as in turned off at the disconnect. The furnace is powered 'on' only when you want to specifically test the effects of the air handler, such as during a Worst Case test. The little bit of makeup air used by such a furnace rarely contributes significantly to depressurization but interzonal competition from unsealed or imbalanced ducts can be huge. You can have a tight shell but a zonal conflict btw one part of the house with another that can cause infiltration. For instance, returns are fixed orifices while supply registers can be closed. If you close off a few supplies, such as in a seldom used room, you can create an imbalance in the system. More air gets sucked out at the return but not enough supply air enters the space to balance it resulting in a localized or microclimate depressurization.

When there is a radon system installed, it should be tested for depressurization. First turn off the radon fan and get your baseline Stack Effect WRT outdoors. Then turn on the fan and repeat. The difference is how much, if any depressurization is being caused by an improperly sealed radon sub-slab suction system. Those WRT's need to be recorded on opposite sides of the house, esp. if there is more than a 5mph wind blowing--upwind and downwind sides. Air the infiltration points located at what is commonly the downwind or leeward side of the home?

[stvc]

The N factor is a number from a chart based on your region, # of stories and shielding and is used in a formula to convert to ACHn [natural air changes] from CFM50. It's just another way to look at the data in the real world as opposed to CFM50 [the force of 20 mph wind on the house]. It's not absolute but just another tool. As far as the test it is an odd feeling the first time you experience it, you are indeed in negative pressure, -50 pa and is normal. It doesn't matter if the house is leaking allot or not, it's still -50 and that furnace should have been shut off.

The lack of house wrap may be a factor here, it could be leading to leakage withing the walls that is fairly well sealed to the inside. it deserves more thought.

As far as another test I would have the first one back since since you have had no follow up and they included it. You don't really have anything to lose and it may have been a simple mistake like having the gauge set for the wrong ring and they missed it. Since they then thought it was real tight they cut off the search for leaks too soon. Just a guess but nothing to lose by giving them another chance.

[taverty]

The furnace wasn't on when the test was conducted, she set the thermostat to off before the test started. But as soon as the blower was powered on we noticed the display went off on the thermostat. It's a power stealing thermostat, so the control board in the Trane furnace shutdown the power to the thermostat. The display only came back once I power cycled the furnace breaker after the blower door test. The furnace has a single metal draft assisted flue going up and out the attic.

As far as I know they didn't conduct any worst case depressurization tests. She didn't run any tests with the basement or attic unit running.

At the time I had the audit, I didn't have the active radon fan. It was installed a few months after. So I'll ask them to include the radon fan in the new tests.

[taverty]

stvc, makes sense. I'm going to request the test out now. I'll post back the results after the test. I'll also ask if they have a smoke machine. Even if I have to pay extra I think it's worth it!

Thanks!

[energy_rater_La]

this may be obvious...but sometimes obvious things get over looked.
as the first test was prior to mechanical ventilation install, make sure
that the mechanical ventilation is sealed off prior to testing or it
will skew all the readings.

test in ..test out (or pre & final testing) was this included
in the cost? if so, then use thie final test out for the next round.

"The lack of house wrap may be a factor here, it could be leading to leakage withing the walls
that is fairly well sealed to the inside. it deserves more thought."
I agree. since reading that there was no wrap behind brick/vinyl this has been on my mind.
how in the heck did it pass code?
bricks don't stop moisture, and vinly is a very leaky product...why have there been no
moisture intursion issues? maybe some of the blue in the thermal scan of the walls
was moisture??
I dunno. still thinking abou this.

as I have no exprience in basements or radon vents...I'll leave that to those
of you who do have experience with these areas.
water table is too high here in La for basements, and radon is very low here.

and hearthman...back on the first page traverty talks about a mechanical
ventilation system installed after blower door test by another company.
just fyi.

[hearthman]

We've covered so much ground here, I'm kinda' losing track. I see where it appears they installed an HRV after the test, correct? Calling it "mechanical ventilation" was confusing me. An HRV properly set up normally does not affect the ACH and is not used for MUA--it is balanced in and out.

One question for the OP: where does the NPP tend to lurk? Is it down about belt level on the first floor or higher up?

Brick veneer makes for a pretty tight envelope in some cases but can leak like a sieve depending upon how the drainage plane is managed at the top. If they used #15 felt or even grade 'D' building paper behind the brick veneer, that is not an air barrier so like ER La said, the ext. sheathing could be the source of the leakage.

Glad you clarified about running the furnace during the test. They should have been clear about that. My recommendation is to place a low level CO monitor in the CAZ during the test to protect everyone in the building. An off the shelf UL listed CO alarm is junk and can get you sick or worse. Not always practical to keep running back to the CAZ with a combustion analyzer during the test, esp. with 3 floors.

Vinyl siding is designed to breathe so it can dry to the exterior just like a rain coat. Brick veneer absorbs water then either dries to the outside or water is driven by vapor diffusion towards the dry interior where the drainage plane 'catches' it so it can escape at the weep holes providing no one plugged them up. A lot of masons are using plastic vents in head joints to allow venting while allaying anxieties over the possibility of bugs entering through the weep holes. An IR camera can be very useful in locating occult water penetration but you need about a 10*F temperature gradient to really see because it works off temp. differences to adjacent surfaces. This means IR thermography sometimes has to be scheduled at extreme times in the day to get enough delta T. Note that IR thermography is not an X-ray of the building though many think it is and some tout it that way. It shows surface temps. where its up to the operator to put those temps. into perspective such as missing insulation vs. moisture. A quality pin-type moisture meter with training are advised along with training & certification for the thermography.

[billygoat22]

I had another though or two.

the chase/clearance for the flue pipe up out roof could be air flow route.

the floor joists at each level could have openings to the exterior of home (band joists run around perimeter and floor joists butt into them). its likely plywood joints hit right at thsoe locations as well, giving lined up gaps for air intrusion. I'm assuming there is plywood on 100% of exterior as sheathing

bathtub plumbing openings in floors, the stud cavities around the tub, an if a tub unit w/ integral top or has dropped ceiling over tub, plenty pathways there from floor to floor or into attic if on top floor.

pvc radon riser, other plumbing, duct risers and the gaps around where penetrate floors

voids inside walls where framed out for soffets, angled walls, etc.

all these could be interconnected paths for airflow inside the walls where you can't see all them.

Had one customer, return was in closet floor pulling through louver in door. the tub access door was gone, had been pulling air from attic through drop ceiling above tub, into wall studs and down through space under tub into return ductwork. sealed it up and his tub doesn't get cold in winter, hot in summer.

you might try looking for "builders guide" book for your climate, Joseph Lstibureck

[billygoat22]

seen plenty of cases, where insulation was stapled up, but there were voids in walls under the insulation, sometimes it falls down and you can see inside walls and feel the warm air leaking up

[stvc]

There certainly are many hidden places for leakage.

Taverty - when the next blower door does get done make sure you have plenty of time to search around with it running. I'll see if I kind find a good list of places to look and post it.

Still curious as heck to see if this one turns out different.

[energy star]

Are they phony windows in the attic? Are they sealed?
If you removed all the insulation in the attic you would find the hole in the top floor ceiling. It may be under that platform.

If you are sucking massive amounts of air (negative pressure) into the return, bringing all that air into the attic, condition it, and then you spit it back into the house. But.....if you have supply air duct leaks into the attic, and not all that air makes it back into the dwelling, you create the exact problem you have.

Yes. You should remove ALL the insulation on every duct in the attic, seal all connections and reinsulate.

[energy_rater_La]

stvc wrote:
The lack of house wrap may be a factor here, it could be leading to leakage withing the walls that is fairly well sealed to the inside. it deserves more thought.

we have covered a lot of ground in this thread.
but for a minute lets go back to the stack effect, air in...air out...where this all started.

I've been thinking about small cracks that have a large effect & where air
gets in and gets out. no great big smoking gun so far...maybe there isn't one.

so what about a smaller sized opening...that just keeps going on & on through out
the house?
just imagine that behind the ceiling moldings & behind the floor moldings that
you have a gap that is covered..much like the gaps hidden by bath vent fan covers
& supply grills.
only this gap is 1/8" to 1/2". not so big is it? but look at the linear feet of each wall.
this adds up big.

if this gap is behind the ceiling molding, extreme attic temps are on one side.
if the gap is behind the floor moldings, temps are less extreme, but still
problematic. air in...air out.

while this usually is an older house issue,
but in new construction, not all sheetrock finishers seal
this gap.
this is why I tell homeowners to tell finishers that they are not
installing ceiling moldings..this way this gap is taped & floated.

finish carpenters install moldings, painter may or may not caulk..usually
not, or not continuously. in my experience caulk stops above eye level.
check the top of a door frame & you'll see what I mean.

there is a method of installing sheetrock known as ADA. air tight
drywall approach. everything caulked, taped & floated for tight
air barrier on interior of walls.

sometimes we have to live with what we can't reasonably change...
like lack of house wrap behind brick/vinyl. but what we can access
is air sealing of walls from inside of house.

there are times we get so focused on air sealing...that we lose
sight of the bigger picture.
simple things like the air barrier to the attic.
you can't always seal all of it from the attic,
so you come inside the living space & continue the seal from inside.
clear caulk is a great thing! just wish there was a caulk that dried
to a matte finish, instead of a shinny finish.

even the fireplace, from the attic, seal what you can.
then come inside and continue the seal.

I often find leakage at ceiling moldings at top of brick fireplaces.
After sealing opening at fireplace from inside the attic...I caulk inside the room
@ fireplace.
Mortor joints first, then once that dries, a continuous bead of caulk
from molding to brick. then the top of the molding to the ceiling.
between the attic sealing & the interior sealing... you can do a heck
of an air sealing job. and a secondary line of defense is a good thing.

during blower door test...these are areas to check for leakage.
get on a ladder & feel at top of molding @ ceiling,
@ bottom of molding @ wall. wet your hand so that you'll
feel if air movement is slight.
same with floor moldings. feel at floor of uncarpeted room & at top
of molding to wall.
feel the tops of door frames & window frames...you'll see what I
mean about painter stopping caulk ...at eye level.

now OP if you don't have ceiling moldings...this post has been a waste
of time!

I agree that ducts should be sealed. been thinking about that too.
I wonder about ducts being depressurized @ 25 pa. and once ducts
are pressurized...if the pressure was increased.
it is hard to find leakage @ 25 pa. but up that pressure, and leaks
are easier to find.
108 cfm of duct leakage..spot on 5% for a 5 ton unit.
and that doesn't come easy, sealing to 5% EVERYTHING has to be sealed.
I've never tested a duct system that achieved 5% total duct leakage.


as for the duct system, it is a sheet metal trunkline with flex supply ducts.
I don't agree with removing all the insulation on ducts & trunkline
in the attic, I do think that
the ducts should be mastic sealed.

unwrapping the sheet metal trunkline, mastic sealing every seam, re-insulating the
trunkline..that is a lot of time effort & money.
I think it could be better spent by mastic sealing flex duct collars, plenum corners,
plenum seams & plenum connections to equipment.
supply box penetrations & return air sealing.
that is where I'd focus.

these small leaks add up to a large leakage amount.
you'll have to weigh costs vs benefits on some of this stuff.
hopefully auditor/rater can weigh in on some of this based on their
experience in your area.

I'm not saying that these are the only solutions...just adding some
food for thought. the whole no house wrap or anything on OSB walls..
kinda threw me for a loop. once I moved past that...I started thinking
about keeping air out of walls...blah blah blah.

Have a wonderful Easter everyone...see y'all tomorrow evening.

[stvc]

Erla - I agree, but up to this point the blower door and duct-blaster say this place is super tight, which is so contrary to all the symptoms. Puzzling.

Just patiently waiting that next test now to see if there is an A-HA moment coming. If not this is going to go down as text book training exercise when it is figured out!

The last "no house wrap house" unfortunately for me was mine! It had defective masonite siding and needless to say I replaced a lot of OSB. I can only imagine under that vinyl that isn't really waterproof there are, or going to be some holes going on. If it is part of the puzzle here I can't say for sure but obviously it's not good.

Happy Easter to you as well.

[dan sw fl]

The duct blasting tech noted that since we have 9' ceilings on all three floors he thought that could be a contributing factor in raising our neutral pressure plane. \

Also, since the duct blaster tech was surprised to hear this I thought it may help here. My home doesn't have any house wrap, no TyVek, just brick veneer front with vinyl siding on the other three side, then under that OSB.

I don't know if it matters, but our house is actually 5,000 sqfeet. I mentioned it to the audit company but she said it just needed to be a rough estimate.
I'm mentioning it now since I'm grabbing at anything!

She offers a test out, which I was going to take advantage of, I really wanted to do it at the very end.
But at this point I should have her out again.
My downstairs unit is a 3.5 ton A/C 100BTU furnace (80% efficient).
My upstairs is a 2.5 ton heat pump, not sure of the electric coil BTUs.
When they come on though it's nice and toasty, but all I see is dollar signs!!!

Thanks again!

How do you know ACTUAL furnace efficiency?

Location?
House Age?
Monthly electric and gas usage.

[energy_rater_La]

house in Maryland
built 2004

sq ft is 5000 & blower door is 2400...
and the ductwork 108 cfm of leakage.

both house & ductwork are unusually tight,
going by information posted.

OP hasn't posted utility costs.