Negative House Pressure

[precision hvac]

Negative pressure in house (the title of your thread) would point me 1st to look at the duct system & leakage.
Had one last week that was so bad on supply side that when the furnace came on, it would cause all the smoke from fireplace to fill the room.
I'd slow down on throwing a bunches of fixes in the mix & find out why your home is going negative.
Duct blaster by a HERS rater is where I'd start 1st.

[dan sw fl]

when you put in the whole house system, this doesn't address the
stack effect, this is a fresh air exchange system.
this allows you to continue to tighten the house, with fresh air
being provided by whsystem.

best of luck.

So, why wouldn't mechanical ventilation mitigate negative pressure?

April Aire model 8126 does not seem to be an EXCHANGE system.

http://www.aprilaire.com/index.php?z...y=16&item=8126

[energy_rater_La]

www.resnet.us
for energy rater in your area.
we do duct testing on every job.
talk to several raters and get someone with
experience in existing homes. discuss the issues
you've shared here.

best of luck.

[energy star]

You can not make a house to tight

[taverty]

Thanks for the input. I'm going to call around and get a duct blasting done. From the site that energy_rater_la posted there seem to be quite a few in my area so it shouldn't be too hard to find someone.

Also, as requested I'm going to take some video/pics of my attic and ducts and post it. I agree, a picture is worth so much more.

I purchased one of the those Black and Decker thermal leak detectors:
http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1

I found that there was a 14.1 degree difference between the ceiling next to the return and the filter in the return. 65.3 ceiling, 51.2 aimed at the return duct. I also found similar differences when I aimed it at most of my supply ducts. Only two supply ducts didn't have any drastic temp difference.

So maybe my duct system is the problem. However, wouldn't I expect the ducts to be colder since they're technically in unconditioned space? But 14 degrees does seem drastic!

I hope to get home tomorrow before it's dark so I can get some good photos of the attic.

Thanks again!

[energy_rater_La]

take some pictures of the returns from both outside the return
and inside if possible. also, check where plenums connect to equipment.

looking forward to the pictures.
I had that black & decker temp gun..someone borrowed it...now just have raytech.
oh well...

best of luck.

[taverty]

I was able to get some video this afternoon. Hopefully it isn't too dark:



There are some pictures at the end of the video with comments. They show the leaky fireplace, downdraft and return ducts. Let me know what you all think.

Thanks again!

[billygoat22]

One thing I've noted is that airleaks under attic insulation show up as dirty spots on top of the insulation.

You didn't mention how many recessed lights you had.

also, what type house is it upstrs?- dormers? garrison style w/ overhang, knee walls like in a cape cod? these can introduce a lot of leakage points.

I'm also curious as to how the (manufactured) fireplace is set up. I've seen them leak profusely around the edges or through unseen openings in the cabinent. If its on an outside wall, there may be other leakage points beside the flue. If its not in use, tape up the flue opening while leaving door open and see if the draft stops.

You could also have some voids in the house structure used as part of the duct (panning) and an opening in the voids to outside somewhere that didn't get sealed up.

[jtrammel]

The duct system looks on the better than average scale for my area, but looks can be deceiving. In an attic duct system it is crucial to capacity/efficiency to have the ducts sealed and insulated very well. It could be dominant supply leakage causing the negative pressure but I don't think that is the only factor because you sat the drafts happen whether the unit is on or off so it just contributes to the negative pressure you already have. Does the range downdraft have a backdraft damper on it? Maybe the downdraft piping is loose somewhere if it does have a damper. For the attic pull down the make something called an attic tent that may be worth looking into. Have a BPI or RESNET certified energy auditing company do a home energy audit done. It seems the other rater missed whatever it is that's causing you these problems. If you really want the attic to living space boundary sealed then get it spray foamed. It is worth it if you will be in this house the next 15-20 years. You still will need to find out the points where the air is entering (stove/fireplace etc) and seal them up too but stack effect will be reduced greatly and your ducts/air handler will then be in semi-conditioned space rather than a 20*F/120*F unconditioned attic. Sorry we can't figure out exactly what's going on because we aren't on site but find a good rater in your area and they will get to the bottom of it www.bpi.org www.resnet.us www.comfortinstitute.org let us know the outcome of the testing when you get it figured out.

[hearthman]

Hard to see and hear a lot but a few thoughts:

The inner collars need to be sealed with an approved duct mastic, a 150lb UV rated zip tie (black) then imprinted UL 181 a/b-FX butyl-backed foil tape between the vapor barrier and trunk and another zip tie.

Ducts must be balanced but supply leaks in an attic will result in depressurization.

Inspect each supply boot. Ensure each is sealed to the drywall ceiling with duct mastic or above tape. Make sure the return penetrations are well sealed, too.

All ceiling penetrations must be sealed. Any gaps such as missing top plates must be sealed with fireblocking approved per your local code or the IRC R302.11 Don't forget around plumbing vent stacks and wiring chases.

Replace all recessed ceiling lights that are not ICAT rated with those that are.

Allow some passive infiltration below the Neutral Pressure Plane.

Provide adequate makeup air for large exhaust fans interlocked to the exhaust fan.

Conduct blower door tests with IR thermography and combustion analysis during a Worst Case Depressurization test.

[energy_rater_La]

replied on other thread, as this one was down for a while earlier.

but I forgot to ask...is that a damper on the trunk line?

finding duct leakage can be done with reversing air flow of blower
door and feeling in attic at ducts/returns. measuring duct leakage
by depressurizing with blower door isn't as accurate a duct blaster,
but pressurizing to find leaks, either works. just fyi.

IR cameras are a nice visual for homeowner...but not always necessary if tech knows
what they are doing & understands how things are constructed.

best of luck.

[taverty]

billygoat12, the house is a fairly standard colonial. The dormers in the attic are decorative.

The gas fireplace sits in a cantilever on an outside wall. It is really drafty, air mostly comes from the bottom and boy does it come in! Some air comes around the sides but not like the bottom.

jtrammel, the downdraft doesn't have much of a back draft damper, it's just three fins on the outside vent. Sometimes they don't close all the way and I have to adjust them to get a better seal. Maybe I should add an inline back draft damper instead of relying on the external vent hood.

energy_rater_la, that is a damper on the trunk line. I think it's there to limit the air going to that short run between the rafters.

hearthman, thanks for the information on the ducts. They definitely aren't sealed and zip tied like you specified.

Thanks for the information. I'm definitely going to have another audit company out. I will report back here with what they find.

[Shophound]

The gas fireplace sits in a cantilever on an outside wall. It is really drafty, air mostly comes from the bottom and boy does it come in! Some air comes around the sides but not like the bottom.

Remember the building science dot com article I linked to earlier in this thread? He talks about fireplaces like yours in the article. More than likely, little to no insulation, and definitely no air sealing, is what you'll find inside the cantilevered enclosure surrounding the fireplace.

jtrammel, the downdraft doesn't have much of a back draft damper, it's just three fins on the outside vent. Sometimes they don't close all the way and I have to adjust them to get a better seal. Maybe I should add an inline back draft damper instead of relying on the external vent hood.

If you were to install an additional powered damper in the stove exhaust duct, the damper motor (actuator) should have an end switch that prevents you turning on the exhaust fan until the damper is fully open. Additionally, you would want a damper with seals or gaskets on its edges so it provides an airtight seal when closed.

energy_rater_la, that is a damper on the trunk line. I think it's there to limit the air going to that short run between the rafters.

These are balancing dampers. The duct install in your attic does not look all that bad; I've seen far worse. In your video you pulled back insulation where a branch duct connects to the trunk, and revealed lack of air sealing at this location. Don't be fooled that covering these locations with the insulation stops the leaks. It does not. Fiberglass insulation does not stop air leaks, it only filters air leaks. These connections need mastic applied to the take-off collar, the flex then reinstalled, banded, more mastic, insulation pulled over, banded again, and a final coat of mastic. That's how to do it right. What you have now is contributing to the stack effect in the house, the cold air dropping out of the return, and potential depressurization of the house when the system is running.

hearthman, thanks for the information on the ducts. They definitely aren't sealed and zip tied like you specified.

Thanks for the information. I'm definitely going to have another audit company out. I will report back here with what they find.

Please see my comments above in bold type.

[energy_rater_La]

it is a nice looking duct system IMO. can use some mastic to seal it up..but
not a bad job at all. we have all seen much much worse!

sealing all these areas will force fresh air to come in via mechanical system installed
instead of sucking & blowing throught paths of least resistance.

take a look at this article about cantilevered areas. I think this applies to
your fireplace situation. if you get a chance, post a couple of pics
from basement looking into fireplace area.

http://www.energyvanguard.com/blog-b...lding-Envelope

best of luck.

[hearthman]

Walls tend to not leak until you put holes in them. A fireplace cantilever and chase or "dogshed" is full of opportunities for air infiltration as the Hound stated. The cantilever itself is rarely properly air sealed or insulated. Remember, on a cantilever, you have the air seal to the subfloor the fireplace sits on and its attending framing above plus the joist bays where it penetrates the foundation wall. If you're lucky, there will be a few batts of fiberglass insulation stuffed half-hearted into these bays with no air sealing. If the underside of the cantilever is accessible, remove the plywood outer sheathing and insulation. Then foam/ caulk/ seal every seam religiously. Fill the bays with fully fluffed insulation with no gaps. Replace sheathing with a bead of caulk circumferentially. Where the bays are accessible from the basement/ crawlspace, block off the bays with duct board, Thermo-ply, Thermo-pan or any suitable draftstopping and caulk it in with duct mastic.

Now, open the chase. Remove all insulation. Seal every seam/ gap with foam/ caulk/ mastic. Re-install insulation making sure it is fully fluffed and fills each bay. Sheath over the inside of the chase with Thermo-ply or equivalent ensuring all the seams are sealed with UL 181-butyl backed foil tape and foam/ caulk/ mastic joints to wood. Before closing the chase in, wipe down the outer wrap of the fireplace with a citrus-based solvent cleaner to degrease it and remove sources of odors. What you are doing is bringing the fireplace inside the thermal envelope of the house. Once the chase is properly weatherized, cold air will look elsewhere to infiltrate. Sealing the upper levels will minimize the tendency to infiltrate as will sealing and balancing ducts. Having your HVAC system located outside the house will always present a problem with passive reverse stack effect as La Rater discussed. All you can do is seal, seal, seal then insulate appropriate to your DOE climatic zone.

[energy_rater_La]

I'm loving this thread!

[energy star]

Return duct to master goes up to attic ridge vent, pretty hot up there. Then it goes all the way back down to the floor. Looks like it goes below the attic trusses (floor) Why do I see truss bottoms by the return flex duct going down to master bedroom? Do you have a tray ceiling? Is there an open void uninsulated? Buy a gallon of duct mastic and cut back all necessary insulation to expose that connection and brush on mastic. NO TAPE. The plenums need to be sealed along the edges. Almost looks like they need to be knocked together better. Take a razor knife, make an eight foot cut through the duct insulation right down the middle on the main trunk itself. You will then see the actual main trunk connections, are they sealed? Nope. It looks like one side off the main trunk has a closed damper? Why? I may be wrong but check it out. Install a reflective barrier in the attic. That will help a lot. Why do you have condensate pump instructions in the attic? Gravity is your friend.

[taverty]

Sorry for the delay. My 2008 Mercury Mountaineer decided to have it's front differential self destruct! So I spent this past Friday under the truck fixing that! I wanted to get into the attic this past weekend, but I was pretty worn out after doing that replacement.

I attached photos of my leaky bump outs. From everything I read, I have to make the top of the house as tight as possible before attempting to fix the bumpouts on the lower level.


Here's a pic of my kitchen bump out. The cabinets in this bump out are at least 10-15 degrees colder than the cabinets around it.


Underneath of kitchen bump out.


Fireplace dogshed. I don't even think the inside walls of the dogshed are insulated. I looked through the gas line knock out on the bottom of the fireplace and all I see are studs and plywood!


Underneath of fireplace dogshed


Basement view of kitchen bump out. A lot of black fiberglass and cold air comes from this area.


Basement view of fireplace dogshed. Here is the insulation they stuffed in the cantilever bays. The insulation doesn't feel like it does much, big drafts coming from here.

Short of tearing of the outside siding and rebuilding these cantilevers I'm not sure there's much I can do. I'm going to have the insulation company remove the FG insulation and spray foam these areas hoping to cut down on the airflow. But again, I heard that I needed to slow down my loss at the attic before sealing these areas. Maybe these areas are so bad that I should do the reverse?


-----
energy star, I don't have a tray ceiling and there aren't any voids. There is a mechanical platform, it looks like they folded batts of insulation and stuck it under the mechanical platform.

You're probably right that the main trunk lines aren't sealed, but is it worth it to cut back the insulation on the main line? I was thinking of just sealing all the flex connections to the boots and main trunk. Do you think that's enough? That damper isn't closed, it's just half closed. It's to that much shorter run on the right, I think they're trying to make sure most of the air goes to the left in the longer trunk line.

That isn't a condensate pump instructions. It's a shutoff for the overflow pan that the air handler sits in. I've never actually looked at those instructions, the builder's HVAC tech left them there.
-------

Thanks again for the help!

[hearthman]

You can get someone to pop the siding off the dogshed and weatherize the chase as I prescribed. Same for the cantilever, which was as I suspected.

A Duct Blaster test would guide you towards the most effective duct sealing. Often the biggest offender is not the most accessible or visually evident. It's hard to go wrong spending money sealing the upper envelope.

You have a Heat&Glo or Heatilator gas direct vent fireplace I see. Do NOT allow insulation to come in contact with the outer wrap in that dogshed. It must maintain the stated clearances to combustibles. However, the co-axial vent system may be leaking some. You are allowed to caulk the outer joints and firestop penetrations with high temp. silicone caulk. Be sure to caulk where the DV pipe enters the outer wrap of the fireplace and ensure the unused takeoff is factory sealed. These units have rear and top take-offs. Sometimes, techs will begin to open one, then realize they were supposed to vent it the other way so they may throw the old shipping packing and cover on haphazardly. This is best left up to a pro familiar with this brand fireplace.

Contact FireSide Hearth and Home in Annapolis Junction for weatherizing and inspecting the fireplace. That is the Regional office so they are the most likely installer of the fireplace for the builder. They are owned by the mfr.

[energy_rater_La]

this is what I thought was going on here. your pictures just confirmed it.
now you understand the link I posted in relation to your situation?

so you actually have two situations of bump outs.
one at fireplace & one at cabinets (??)

that neither of the bumpout walls are insulated, contributes to the temp diffrences.
so you have choices as to how to deal with them.

easiest would be just to foam from basement where cantilvered joists exit
walls. this would stop air movement, but still leaves a big uninsulated area of wall.

harder would be to open the bump outs..fireplace from under deck at floor of bump out..
then foam the walls, fit foam sheating to bottom of bump out, air seal and replace osb sheathing.
then from inside basement do the final air sealing.

the other bump out..no access from underneath? then take off vinyl open wall
foam, foam sheath opening & air seal then replace osb, re-install vinyl.

just as you seal joists thru bottom of wall..you have to check at top of the
bump outs for the same situation.


foam insulation would be faster & easier, but I beams at openings make it
easier to seal than space joists. if you use foam sheathing you fit it tight
& caulk it in place. so, I disagree with your energy rater on that one.

and not now..but later explain the radiant barrier in pic five.