Negative House Pressure

[hearthman]

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.

If those numbers can be trusted which I'm beginning to question.

[taverty]

The wife won out and I didn't get to do any additional investigation this Easter weekend. I was bummed, but I completely understood her.


hearthman:

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?

I'm not 100% sure how to scientifically measure the NPP, neither the audit company of duct blasting company said absolutely where it is. The duct blasting company said it was probably 3/4 the way up the first floor. Making it above the fireplace and downdraft cooktop.

I'm not sure what's behind my brick, I do have the little plastic weep pipes at the typical locations. I only found out I didn't have house wrap when I installed my deck, I pulled back the siding and there was just plywood! I contacted my builder and he said he didn't believe in house wrap! This is the same builder that didn't believe in a ridge vent, he put in a powered attic fan instead of installing the ridge vent. Thanks builder!! The plywood seemed dry after 8 years and there were no signs of rot anywhere. I wasn't able to check that far up the siding because the deck connected at the rim joist.


billygoat:

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.

You have a very good point here. My master tub is right above the leaky kitchen bump out. On top of that, there is a soffit that runs the perimeter of the kitchen. See pic below:




energy star:
The phony windows in the attic are not 100% sealed but they are closed. They have a very slight gap at the bottom where the sash meets the sill.


energy_rater_la:
Thanks for the information as always!
On my second floor there are no crown moldings that were installed by the builder. So the wall to ceiling joint was plastered. However, the first floor has lots of crown, and knowing this builder I'm sure it wasn't sealed correctly. I still plan on putting mastic on all the flex collars. Much easier to do it now without all the extra insulation. I requested that the insulation company bury as much of the duct system as they can under the blown in FG.


stvc:
I'm working with the past audit company to come back out and do their test out. I will definitely post back what they find.


dan sw fl:
I have no idea what the actual furnace efficiency is, I was giving the value that was on the yellow sticker on the side of the furnace.
My propane cost is difficult to estimate. I have a 1000 gallon tank buried in the yard and I have it filled once a year. So I really have no idea my month to month costs. The electric is ~3,500-3,700 kWh/month when it's really cold outside. I know it's mostly my heat pump because in transition months my electric is ~1,500-1,800 kWh/month. And this is with a propane furnace doing a lot of the heating.


I will definitely let you all know what the audit company finds and if I find anything once I get back into the attic.

Thanks again!

[billygoat22]

I just about guarantee they didn't sheet rock, then put up the soffet. so the floor joist spaces, wall cavity spaces, and the recessed lights are all open to each other. also, the intersection of the floor joists and up/down walls meet there in back of that.

don't know if theer's a roof on that bump out there, or if it extends up and the tub sits in a bump out on second floor.
if the first, roof structure could also be open to that soffet as well. depends how the sheathing was done on exterior of house

is the tub set into a base, or is it a standard built-in unit? the underside of tubs are open throughout, and usually there is no drywall behind the tubs to seal off from wall cavities.

[stvc]

The NPP can be found using the manometer from the blower door [or any that measures pa]. Just zero it outside then using a hose long enough to reach outside [sealed somhow] move up and down the strairwell. You should see it go up and down, zero is neutral. Those soffits usually are cuplrits, but until I see some new BD numbers I'm going to hold off comment there.

[energy_rater_La]

I'm curious about the numbers also.
something just seems off.

btw...you know you can test the ducts with the blower door?
we did this before duct blasters became so available. the
duct blaster is more accurate so using the subtraction method
became a thing of the past.
while you are testing the house, I'd ask to do it anyway.

tape off supplies like for duct blaster testing.
tape off return air (s).
after house leakage numbers have been noted,
& pressure has stablized, go to the return.
slowly peel back cover of r/a.
feel the air comming from the area uncovered.
( I usually start at one corner, so that I can feel the amount of air
that is comming out)
once r/a is opened, that number is recorded.
subtract whole house number from open return number..the
difference is duct leakage.
see if this number corresponds within 10% of duct blaster numbers.

ask when the house is tested, that the fan be open, and record the number.
then insert Ring A into the fan...and record that number.
open fan measures from 2000 cfm up to 5000 cfm
Ring A starts at 2000 to and stops at 3500 I think.

won't take but a few minutes, and having both sets of
numbers will be helpful.

also, older blower doors have manometer gages,
newer are computerized. batteries should be checked
if newer and if the gages are what is used
they should be zero-ed out prior to testing. the
top gage measures pascals of pressure, the middle & bottom gages
measure cubic feet per minute. (cfm)
this zeroing out is done with a small screwdriver and adjusting
by turning the screw on the bottom portion of the gage.

if you do test ducts, once you uncover all the supplies & R/A
then reverse the air flow of the fan..and go into the attic
like you did with db test. with an attic staircase, someone will
have to stay downstairs to open & close the staircase.
turn the fan pressure up..you want to move air thru the
ductwork, and the 25 pa of pressure used to test ducts needs to
be increased.
then feel the plenum connections @ equipment & ducts.
feel around r/a framing at attic floor.

better to do it twice and feel more confident in the findings, than
to always wonder.

explain to your audior/rater the concerns you've expressed here.
sometimes house require more than a preliminary and final testing.
intermediate testing is not uncommon and should be provided if
needed. their job is to give you answers...not cause more questions.
if they can't answer your questions they should find out the answers
& relay them to you.
anything less is just sloppy work.the rates you've been charged are close
to what I charge, if I have to do an intermediate test...I do a minimal charge
for this test. of course I break my fee in half..half on preliminary testing,
the last half when work is completed at final testing of the house/ducts.
I also include a report of leakage & how to seal leaks & any issues found during
inspection/testing. this isn't a resnet requirement.

thanks for providing the answers to our many & varied questions.
looking forward to hopefully having some clarification from
this next testing of your home. I know you are!

btw..we all knew Easter trumps air leakage, glad you took the
holiday to enjoy yourself rather than stressing over the house.
keep in mind that this has been ongoing and isn't going to hurt
anything if it goes on a bit longer.

best of luck.

[stvc]

I just wanted to summarize a few key points made by myself and others before the next test. If I miss anyone’s feel free to add.

Explain to your auditor/rater the concerns you've expressed here. Make sure they know this isn't a quick stop for a final number so they schedule time accordingly and are prepared to address your concerns.

Pay attention to the blower door prep procedure. All appliances shut off. All interior doors open [basement esp. I suspect it is included in calculated volume] all exterior closed like normal.

Be prepared to go from bottom to top feeling for leaks [flashlight and ladder ready] Many have posted common and not so obvious areas, the chimney chase to the basement esp. I had a pretty good list and will try to find it for you. If anyone does please post. During the test open and close doors, this will give clues on the amount of leakage in that area if it slams shut or blows open. Don’t forget the door to the garage, I think you said it was attached.

Press them on the NPP, it's not hard to test and is a key point here.

Hope this all helps!

[hearthman]

About the NPP: it is dynamic. It varies. It fluctuates. It follows the leaks. If you open a window or door below it, zoom, it drops. Open a window, door, or attic access and zoom, it shoots up. Now, if the wind blows against the house, it tilts. Envision a bucket half full of water that you're carrying while walking across broken ground--that's often how the NPP is: undulating and fluctuating. Tilt the bucket to one side the the other, that's sorta how it would appear during wind gusts. An open window on the leeward side would tend to exfiltrate whereas one open on the windward side would tend to infiltrate. Knowing your prevailing winds can often assist with solving mysteries. This explains why passive makeup air systems are unreliable as reported by ASHRAE.

If the NPP is very high, you have upper level leaks and vice versa but you have to put this into proper perspective. How is it with the house at rest and no wind vs. windy vs. no wind but with mechanical ventilation running? The house may behave rather well except when imbalanced/ leaky ducts have air blowing through them. Knowing where the NPP is under which conditions is a snap shot into what's going on. You can locate your NPP with a smoke source held at a cracked open door or window. Start low where the air is blowing inwards and raise it up until it reverses and blows out. That is where your NPP is on that side of the house at that moment under those conditions. Now compare to the opposite side of the house. Try this on the prevailing upwind and downwind sides of the home. Now repeat during the various blower door and duct blaster tests including Worse Case. This can often help make sense of confusing or contradictory readings. Coupled with this is recording your baseline Stack Effect and subtracting that from any depressurization tests to see the net effect of the offending appliance or system.

Fun discussion.

[taverty]

I talked to the original audit company. I explained what's going on and they're coming out next week. They said they're also going to try and bring a rep from our power company who has 30 years experience with auditing homes.

It's funny, when I spoke to her the first thing she suggested on the phone was to have the ducts blasted. When I gave her the numbers from the duct blasting she was very surprised at the results. So it's great you all gave me the suggestion to do it before hand.

I appreciate all of your input because I feel so much more prepared this go around. I really want to find the problem and I'll definitely post back the results. They're coming either Tue or Thur depending on everyone's availability.

stvc:
The garage is attached. The door to the garage shouldn't be open during the test, right? I should just try to open and close the door?

energy_rater_la:
I'll definitely ask for them to confirm the duct blaster numbers. I think they're allocating more time this go around after I explained to them what's going on. I'll also ask them to try the different rings and get the numbers. If I remember correctly, she had a digital unit that ran the blower door fan. I didn't see any gauges, I'll pay attention this go around.

hearthman:
Thanks for the information on NPP. Hopefully they're able to accurately test where the npp sits in my house. They said they will use incense sticks to test for NPP and air source leaks.



Thanks again and I'll post back what they find.

[stvc]

taverty - That is correct, it should be closed but by opening and closing things with the BD running it can be enlightening to see if areas are going positive or negative. If they do it means there is good reason to look more closely.

Glad to hear everyone is on board and look forward to this rounds results.

[energy_rater_La]

gages are older equipment, digatal newer equipment..
I've used my gages so long...I'd be lost without them!

I like to start with all interior doors open, and then as I walk
around pull doors partly closed with about 1" opening.
then the leakage from the room with the door partly closed
is forced out of the 1" opening. gives you a 'feel' for
how much leakage from each room.
if doors are undercut, you can close the door all the way
& feel at undercut.
once you 'feel' the leakage, open door and go to next room.

feel around tub, under sinks at plumbing penetrations.
and see if you can check at fireplace & cabinet bumpouts.
in cabinet bumpout you should feel the leakage between
back, sides and top inside of cabinet.

really looking forward to see what this round of testing
shows up.

don't let utility rep move things along faster than you'd like.

I like the incense sticks myself, used them when my nephew
'shadowed' me on a job to 'show' him where the leakage sites are.
make sure you have a flashlight too.

best of luck.

[taverty]

The company came today, I was bummed it was so warm today. The negative pressure pretty much stops when it's warm out. They said my house is even tighter now, 4.6 exchanges vs 5.06.

She thinks the problem is my upstairs M&W windows. As she was running the test she heard a whirling sound coming from one of our bedroom windows. We looked closely at the window and sure enough, there was an 1/8" gap at the top of the window and air was pouring in. A lot of the windows upstairs had a small gap at the top. Only one was so bad that you could really hear and feel the air flow. The problem is the locking latch doesn't force the window up tight so from a quick glance it looks like the windows are closed. I think this is why she missed them the first go around.

She suggested I address all of the windows and see if I still have the negative pressure when it gets cold again. If I still do, she will have the energy company rep come out and try and determine the problem, because outside of the windows she wasn't sure what else it could be. We also have A LOT of dust build up in our house, esp on all the window sill and blinds. She was thinking it was maybe due to the outside air being able to come through the small gaps.

They did try to calculate my NPP location. It was a little bit windy so they were having some trouble. It was between my first and second floor, so ~9-10' feet from the floor of the first floor, quite high! They did the test with the full combination of my HVAC units running and not running (1 on 1 off, both off, both on). The NPP seemed unaffected by either unit off or on. I think that's a good thing.

So hopefully the windows are the fix!! It seems so obvious now that I should have checked my windows more carefully, but I was so focused on the attic. Mother Nature needs to give me one more cold snap!

Thanks again for all of your help. I definitely wouldn't have been so prepared this go around if it wasn't for the input from all of you!!

[tipsrfine]

So the first people who did your audit could not have noticed the windows were not shutting properly? You should ask for your money back. Their job is to tell you how much air leakage you have and where it is at. Your first audit was a big waste of money.

[stvc]

The company came today, I was bummed it was so warm today. The negative pressure pretty much stops when it's warm out. They said my house is even tighter now, 4.6 exchanges vs 5.06.

She thinks the problem is my upstairs M&W windows. As she was running the test she heard a whirling sound coming from one of our bedroom windows. We looked closely at the window and sure enough, there was an 1/8" gap at the top of the window and air was pouring in. A lot of the windows upstairs had a small gap at the top. Only one was so bad that you could really hear and feel the air flow. The problem is the locking latch doesn't force the window up tight so from a quick glance it looks like the windows are closed. I think this is why she missed them the first go around.

She suggested I address all of the windows and see if I still have the negative pressure when it gets cold again. If I still do, she will have the energy company rep come out and try and determine the problem, because outside of the windows she wasn't sure what else it could be. We also have A LOT of dust build up in our house, esp on all the window sill and blinds. She was thinking it was maybe due to the outside air being able to come through the small gaps.

They did try to calculate my NPP location. It was a little bit windy so they were having some trouble. It was between my first and second floor, so ~9-10' feet from the floor of the first floor, quite high! They did the test with the full combination of my HVAC units running and not running (1 on 1 off, both off, both on). The NPP seemed unaffected by either unit off or on. I think that's a good thing.

So hopefully the windows are the fix!! It seems so obvious now that I should have checked my windows more carefully, but I was so focused on the attic. Mother Nature needs to give me one more cold snap!

Thanks again for all of your help. I definitely wouldn't have been so prepared this go around if it wasn't for the input from all of you!!

I kind of expected they would find something more than that but it does sound reasonable. You could try a quick fix with some of that removable caulking, forget the exact name but it's like sticky rope you just press on. The NPP is pretty much where I would expect but will probably lower when you seal the windows and improve the infiltration problem.

I hope it is it and all will be well now, let us know!

[hearthman]

I told you I thought something was off! At least you're making progress. Sounds like you may need to replace those windows. Check the warranty. A window with a 1/8" gap when latched would not meet the fenestration requirements. You may be able to get replacement sashes without replacing the entire window. Close that gap and the NPP will drop. Wind dying down may make it drop, too depending upon how the wind was affecting your home at the time.

[mark beiser]

Double hung windows are the DEVIL!

[energy_rater_La]

Thumb Gum removable rope caulking.

[taverty]

Here are some pics of the windows in case anyone else has this problem. I measured the gap and made shims out of 1x8. I'll probably replace the windows at some point. But if this works I'll probably hold out on replacing the windows for a while. I'll also probably put a bead of caulk around the shim to make it harder to notice the shim under the lock.

[tipsrfine]

Double hung windows, at least the older ones, are way better than new windows.
http://www.youtube.com/watch?v=ELsImfavqF0

[stvc]

Double hung windows, at least the older ones, are way better than new windows.
http://www.youtube.com/watch?v=ELsImfavqF0

Good video and system but IMO some sealer [primer etc.] should have been applied to all that bare wood. Rot and warping are what I see kill wood windows.