Air sealing satisfaction.

[TradEddie]

I've been doing on-going air-sealing around my house as time allows for more than a year, with limited measurable success, but tonight, with 10F outside to help locate problem areas, I hit some electrical outlets in the bedrooms. The first I could get through a crawlspace, and the fiberglass all around the box was totally discolored from filtering the exiting air. The second was only accessible from the front, but the receptacle box was completely filled with dust.

I have often wondered if I'm achieving anything with this, but tonight I saw for the first time unequivocal evidence of the quantity of air I'm losing through leaks like these. Hopefully eventually I'll be able to see the benefits in my heating bills too.

TE

 

[midwestcoast]

Nice to get some satisfaction out of a tedious job. Every little bit helps.
Maybe you've already hit these, but the big game for air sealing is usually found high and low. Attic and basement. This is where air pressure is driving air out (attic) and in (basement). Not as noticeable as in the living space, but there can be lots of air moving out of sight.
Attic hatch, chimney, plumbing stack, pipe chases, can lights, soffits, cantilevered floors, missing headers, sill plates, utility feeds all can be big leaks. In my house I had open joist bays running from under my 2'nd story floor straight into a side attic. Hmmm, why is this floor always so cold?

 

[TradEddie]

I've been hitting all of those areas, a few minutes here and there, as much as two kids any my own other hobbies allow. I just wish I could notice an improvement to show for all that work. Sure, I can see better IR temperatures around the sealed areas, but with last year's mild winter, no noticeable reduction in heating bill. Downstairs receptacles are somewhat satisfying because you can feel the draft entering, but upstairs I was happy to see signs of exfiltration after several nights of sealing receptacles in other rooms.

I'm leaving the attic to last, its a poorly ventilated, cramped cape crawlspace, with 35 years of mice droppings, carpenter ant infestations, mold, exfiltrated dust and general unpleasantness.

TE

 

[semipro]

I've been working on sealing up air leaks too and came to the conclusion that I was wasting my time sealing them up from the inside. If I sealed one hole it only seemed to increase the flow at other areas like interfaces between the chimney and walls. It was obvious much air was making its way into my walls from outside (along with moisture).
I spent some time researching and it seems that you should create a single air-seal envelop either at the sheathing or the inside walls (e.g. airtight drywall). In my case it was easier to establish this envelope at the outside (house wrap, foam, tape, caulk).
I think the point is that you need one "good" air barrier and that creating partial ones both inside and outside is not nearly as effective.

 

[TradEddie]

I think the point is that you need one "good" air barrier and that creating partial ones both inside and outside is not nearly as effective.

I have the same suspicion that sealing one leak merely increases the flow through others, partially negating the benefits, but unless I spend thousands of dollars to rip apart my entire exterior, sealing inside is my only option. It costs next to nothing, except for time. Despite its age, my house appears to have insulation upgrades by previous owners, so I'm already in the area of diminishing returns, just trying to correct the glaring errors and problems.

TE

 

[woodgeek]

I've been hitting all of those areas, a few minutes here and there, as much as two kids any my own other hobbies allow. I just wish I could notice an improvement to show for all that work. Sure, I can see better IR temperatures around the sealed areas, but with last year's mild winter, no noticeable reduction in heating bill. Downstairs receptacles are somewhat satisfying because you can feel the draft entering, but upstairs I was happy to see signs of exfiltration after several nights of sealing receptacles in other rooms.

I'm leaving the attic to last, its a poorly ventilated, cramped cape crawlspace, with 35 years of mice droppings, carpenter ant infestations, mold, exfiltrated dust and general unpleasantness.

TE

I spent the last 3 years doing a DIY seal on my attic floor. Overall, I think I am down the equivalent of ~200 gals of oil just from the attic seal (about 20% of original demand). (Also got ~100 gal reduction just from cleaning the metal weatherstrips on my 50 yo windows, putting vinyl vstrips on the horizontals and shimming the locks so all the strips are actually engaged).

So, if the attic work was say 10 rounds in the attic of a couple hours each, after each round I could expect a couple % savings benefit. I could see this sort of gain as I went by (OCD alert) timing my heater cycling (with a stopwatch) and data fitting (a line to duty cycle versus outdoor temp). So, if you are willing to be crazy metering your energy usage, you can get the satisfaction.

OTOH, maybe you haven't hit the big stuff yet. As semi said, a lot of the benefit comes at the end, since air can find other paths. I thought I was done several times, and then discovered leaks (and top plates) that I had missed before. At some stage, looking at snow melting on your roof is VERY handy. If your roof holds snow longer than every other house in the neighborhood, then maybe you can call 'er done. The snow thing is prob the easiest way to confirm that you are getting a benefit.

EDIT: AAh, I see you are saving the attic to last. I wouldn't. Its low hanging fruit. Sealing my (interior wall and gable end) top plates took ~25 tubes of caulk (think ~200' of bead). So, my advice is get a good gun (power?) and good PP. I started out with (nice) paper masks, and was clearly still breathing too much chit. Upgraded to a valved filter respirator and it was much more comfortable and totally protecting. I just wore old clothes (and changed+showered immediately afterwards) but you could also pick up a tyvek suit if you prefer. IOW, like a lot of DIY the tool/gear makes the job go a lot easier.

My rim joists are all hidden by drywall in finished space....

 

[TradEddie]

I've thought it before, but you may be my long lost twin! I've considered correlating duty cycle with outdoor temperatures, I just can't think of a good cheap way to do it, and I won't sit with a stopwatch. I have all the necessary toys at work, so its frustrating to think about using inferior methods at home. I have been tracking my overnight temperature drop in hopes of seeing improvements.

I'm confused about how sealing top plates helps, or perhaps I don't know exactly what you mean. Can you explain? If I have no unsealed drywall penetrations, how does it help? Is it preventing air flow through the stud bays that cools the walls without actually having a leak to/from conditioned space? The areas of my attic that I know I need to hit are the vent stack and electrical penetrations, but otherwise I don't have much.

TE

 

[woodgeek]

Capes can be really difficult. I have a 1960 'side by side' split level. During construction, the house was framed before drywalling, and the attic floor joists sit on 2x4 plates that run at the top of all the interior and exterior walls. The drywallers would leave a small gap between the 2x4 and the sheetrock, to allow expansion. That leaves a 1/16-1/8" gap between the drywall and the plate (on both sides) connecting the attic space to the wall cavities. Multiplied by the perimeter of the house and the length of the interior walls, this little gap adds up to a few square feet of opening (!), easily dwarfing the opening from things like ceiling j-boxes or recessed lights (in my case). How does air get into the drywalled cavity....through the hardwood floor, around the bottom plates (which also have a gap) and other details.

So, I did have to do a plumbing chase and a masonry chimney chase, and sealed a lot of wiring holes (coming up through the top plates), but the major thing for me was ~30' of open stud bays (along the split level) and 200' of top plate cracks.

In capes, IIRC, the kneewall spaces are supposed to be tough....lots of open bays to the second floor joists. To seal cavities, I bought kitchen-sized garbage bags, but a 14" length of FG bat in it, folded it over double and stuffed it in the cavity...the batt holds it in, the bag prevents airflow. PRob not perfect, but easy and fast in a cramped space. In a cape, I might want to call in a pro or get some pro advice about the roof venting.

Recent studies show <1% of air leakage is through electrical boxes in most homes. One earlier study reported 20%, but that was wrong.

 

[TradEddie]

I'll look at the top plates whenever I go up there, but I'd sooner pay the propane bill than pull all that FG to airseal inch by inch. My kneewall crawl spaces were/(are?) a mess, when we moved in, the access doors were held in place with magnetic clasps, and there was at least a 1/2" gap on top of each door. Some 1x2s were placed up under the roofline to try open a channel to the main attic.Needless to say, that was a moldy mess in there. The crawlspaces are floored, so no access to seal the bays running under the upstairs rooms. I put down batts on the floor, paper face down, foam spacers to the main attic, and an insulated plywood inner door pulled tight against the frame. Better than nothing but not ideal.

There were so many other disasters I could list, the fireplace is located in a completely uninsulated brick wall to the garage, with wooden mounting brackets for the mantel penetrating that brick wall...

The odd thing is that the house was built in 1977, but had R13 in the walls, which seems good for the time, and presumably sometime after that, R-5 foam and Tyvek was added outside, yet those huge gaps in the access doors were never looked at...

TE

 

[woodgeek]

Yup. Airsealing was really neglected in the 70s and 80s....noone had any idea (in the US anyway).

Depending on your layout and flooring, your situation can be hard to predict. I remember finding a 'airsealing guide for cape houses' document on the net once, you might google around to see what you can find. There are some common airsealing faults in that layout. I wouldn't worry about top plates much in your case....really a big issue for ranch-ey type houses with big flat attic floors.

i would worry about open stud bays and open joists. So, if you are in the knee crawl, you are sitting on the joists for the second floor, and there is conditioned space to one side. If the crawlspace is unconditioned, you have insulation on the vertical wall and the floor. IF its conditioned, the insulation is on the roofline. In etiher case, I would worry about those joists running under your second floor. I would want them to be sealed, so the (second) floor cavity is not connected to the knee crawl. But I think many builders leave that open, or hope that a FG batt will block airflow. IF they're open, the 'batt in bag' method is a pretty fast and easy way to plug them.

I would be more worried if the second floor is permeable (i.e. hardwood boards) than impermable (e,g, plywood subfloor and carpet).

Of course, you can get a cheap blower door test done to estimate how much of a problem you have in the first place.

 

[midwestcoast]

Yeah, mine's a 1950 built Cape. I didn't seal all my top plates, just the areas where I saw evidence of filtration. Had bigger fish to fry. I also did a lot of reading to figure out how the house was framed & what I could do to tighten it up.
It was HELL just getting access to my side-attics (space behind the knee walls) since no access was provided. I have 2 large & 2 small. I cut a hole in a downstairs closet ceiling and hoisted myself up into one and for another I had to crawl down the ceiling of a stairwell, face first, building a ladder as I went, k. In both cases I found the open bays and no insulation above the ceilings at all. I used the FG folded in a bag to seal the open joist bays, but also put a squirt of Great Stuff along the edges. The 2 small side attics I couldn't access, so I just drilled some 2" holes and filled those suckers up more than half way with cellulose, then I took off the shoe molding, drilled little holes in the floor & sprayed Great Stuff Big Gap to seal the Joist Bays. It seemed to fill them after 2 to 3 rounds. Went through a lot of that foam.

 

[EatenByLimestone]

I've been taking advantage of the strong wind today and have been sealing up a storm. I'm beat, but my upstairs is much tighter. I cheated and am using a plastic window seal over an open hatch to a knee wall. I'll do the actual sealing of the area behind the knee wall when I can pull all of the junk out of there.

I sealed up some big leaks. It's sassyfying.

Matt

 

[GaryGary]

I've been working on a diy blower door.

Its an old furnace blower mounted on a piece of plywood that is sized to go in a window. You mount it in the window with the exhaust facing out and plug it in -- makes a lot of breeze.

I've tested it in my shop, and on high speed it can pull more than 50 Pa in my not so well sealed shop. Plan to try it in the house in the next couple days.

I measure the pressure difference from house to outside with a $10 ebay Dwyer Magnehelic pressure gage that goes 0 to 0.2 inches of water -- so, its basically full scale at 50 Pa. These gages are really nicely made and seem to always be available on ebay. Working on a simple way to measure the flow rate so that I can estimate an actual Air Changes per Hour number.

I picked up the blower motor at the local Habitat Restore for $15, but also got one some time back for nothing from a furnace installer. Most of them have 4 speeds.

I like the idea that I can now take my time finding leaks and actually see the change in pressure drop and flow.

Gary

 

[semipro]

I've been looking for a fixer upper fog machine on eBay. I plan in to use it inside the house to locate air leaks. You fill the house with smoke them pressurize it with a small fan then go outside to look for the leaks

 

[begreen]

I've been taking advantage of the strong wind today and have been sealing up a storm. I'm beat, but my upstairs is much tighter. I cheated and am using a plastic window seal over an open hatch to a knee wall. I'll do the actual sealing of the area behind the knee wall when I can pull all of the junk out of there.

I sealed up some big leaks. It's sassyfying.

Matt

Way to go Matt. That's a good feeling.

 

[woodgeek]

I measure the pressure difference from house to outside with a $10 ebay Dwyer Magnehelic pressure gage that goes 0 to 0.2 inches of water -- so, its basically full scale at 50 Pa. These gages are really nicely made and seem to always be available on ebay. Working on a simple way to measure the flow rate so that I can estimate an actual Air Changes per Hour number.


Gary

Why not a length of (big) round duct, with a anemometer, or a pitot tube and a second dwyer to measure the velocity at the end?

 

[GaryGary]

Why not a length of (big) round duct, with a anemometer, or a pitot tube and a second dwyer to measure the velocity at the end?

I've attached an about 2 ft long rectangular duct to the fan outlet and measured the flow velocity with a Kestrel anemometer. The problem is that there is a whole lot of variation in velocity across the section. There is about a 3 to 1 difference from highest to lowest measurements as I move the Kestrel around. Its also not the velocity profile you would expect in a duct -- its higher on the two edges parallel to the blower shaft with much lower velocities in the center -- just too close to the fan I guess.

I also have this very nice antique Alnor Velometer from ebay -- its basically a pitot tube with an analog pressure meter that reads out directly in velocity. Has several probes and ranges. Just as an aside, these are available on ebay for about $100 and in addition to being a nice piece of history, they are quite functional -- I'd guess they would be north of $2K if still offered today.

In my anal engineer way, I did a 75 point velocity survey yesterday with the Velometer, and I can used it to get (I think) a good average velocity and flow. The flow on high speed is about 2500 cfm. I think I can use this survey and a single pitot tube reading to correlate this to other conditions.

I would like to work out a simpler way to do this, and a way that someone with just a Kestrel or the like could make descent measurements.
If there was some way to even out the flow in the duct so that the velocity profile was more constant, that would be a big help -- any ideas?

Gary

 

[woodgeek]

On the commercial blower doors, I thought the used a longer, collapsible flex duct to even out the flow.

Might find something like that as a 'play tunnel' at a big box toy store....?

 

[semipro]

Gary,
You could build a venturi to measure flow. (image below).
Radial vanes place before the venturi could be used to create a straighter flow if needed.

 

[GaryGary]

Sorry about polluting this thread with the blower door idea -- should have started a new thread.

So, thinking out loud about a simple way to get the blower flow out of the house at the standard blower door test depressurization of 50 Pascal...

The specs below are for a Fasco blower sold by Grainger -- I think the blower I have is quite similar.

When you look at the flow rates vs pressure drop for each speed, the flow rate drops very slowly as pressure drop is added. So with no load on high speed, the blower door does 2400 cfm, and with 0.3 inches of water (75 Pa) pressure drop, the flow is only down by 20 cfm to 2380 cfm. So, for the range of pressure for a blower door test (0 to 50 Pa), the blower flow rate is essentially constant (I think).

So, to determine the flow rate at 50 Pa (as is used in a standard blower door test), could I run the blower at high speed and note the house depressurization on by Dwyer gage (say its 75 Pa), then go down to low speed and note the new Dwyer gage reading (say its 20 Pa) -- then I could interpolate between the two readings to estimate the flow at 50 Pa?

So, in this example, with 2400 cfm at high speed and 1200 cfm at low speed, the flow at 50 Pa would be 1200 + ((50-20)/(75-20))(2400-1200) = 1855 cfm. Knowing the volume of the house, I could then calculate the Air Changes per Hour (ACH) at 50 Pa and be able to compare it to other standard blower door tests.

This assumes that all 1/2hp furnace blowers put out the same flow rates, and I'm sure this is not strictly true, but this Fasco is close to the 2500 cfm that I measured on my used 1/2 hp blower.

Gary

Edit: the blower data is easier to read at the Grainger catalog page at the link below.
Item
Blower
Type
Double Inlet Forward Curve, Direct Drive, With Motor
Speed
4
Wheel Dia. (In.)
10-5/8
Wheel Width (In.)
10-5/8
CFM Range
2400 to 230 @ 0.000-In SP to 1.700-In SP
CFM @ 0.000-In. SP
2400, 1800, 1450, 1220
CFM @ 0.300-In. SP
2380, 1760, 1420, 1185
CFM @ 0.400-In. SP
2350, 1750, 1410, 1180
CFM @ 0.500-In. SP
2335, 1720, 1395, 1170
CFM @ 0.600-In. SP
2300, 1675, 1365, 1150
CFM @ 0.700-In. SP
2210, 1650, 1300, 1080
CFM @ 0.800-In. SP
2130, 1550, 1220, 1010
CFM @ 0.900-In. SP
1900, 1390, 1125, 925
CFM @ 1.000-In. SP
1720, 1225, 1010, 790
CFM @ 1.10-In. SP
1440, 1030, 845, 620
CFM @ 1.200-In. SP
1160, 840, 650, 465
CFM @ 1.250-In. SP
955, 735, 570, 380
CFM @ 1.30-In. SP
750, 635, 490, 300
CFM @ 1.40-In. SP
540, 435, 340, 245
CFM @ 1.500-In. SP
430, 325, 240, 120
CFM @ 1.600-In. SP
320, 215, 150, -
CFM @ 1.70-In. SP
230, 100, -, -
CFM @ 1.80-In. SP
-, -, -, -
Max. Inlet Temp. (Deg. F)
104
Max. Ambient Temp. (F)
104

Catalog page: (broken link removed)

 

[woodgeek]

you could put a damper between the house (exhaust) and the blower inlet. Then close down the DIY damper until the house pressure was -50 Pa. Then you could read the pressure across the blower (which could now be different from 50 Pa due to the damper). If you had a table of cfm versus pressure drop, you could convert to cfm. And you would not have to assume that a house pressure was linear in cfm.

 

[TradEddie]

Wow, if I had the spare time to do that, I would just work a couple of hours overtime and pay someone to do it properly. I have considered a homemade blower to try locate leaks, but actual quantitative results, that's professional work.

Slightly back on topic, my continued efforts have yielded mixed results. One unexpected "problem" is that I fixed two serious leaks in the room containing my thermostat, now the thermostat kicks in less often, so the rest of the house is noticeably colder!

Also, like most people burning wood, my biggest problem is heat distribution, and sealing leaks may make that even worse too.

Thanks for everyone's tips.

TE

 

[EatenByLimestone]

Do you guys think that the orange Great Stuff will do a safe job around the chimney? It's not used for the woodstove. It's used for the NG boiler and traditional fireplace. I doubt that even when the NG boiler is on it gets hot. Other than that I don't know what could be used to seal the space around the chimney. I have kaowool I can stuff in the crack, but it certainly won't stop the air from moving.

Matt

 

[GaryGary]

Wow, if I had the spare time to do that, I would just work a couple of hours overtime and pay someone to do it properly. I have considered a homemade blower to try locate leaks, but actual quantitative results, that's professional work.

Slightly back on topic, my continued efforts have yielded mixed results. One unexpected "problem" is that I fixed two serious leaks in the room containing my thermostat, now the thermostat kicks in less often, so the rest of the house is noticeably colder!

Also, like most people burning wood, my biggest problem is heat distribution, and sealing leaks may make that even worse too.

Thanks for everyone's tips.

TE

I actually had my utility come and do a blower door test -- it was near to useless.

First they decided that the free blower door test would not be free because I had solar hot water -- try and figure that one out.

So, I paid a bit over $200 to have a couple guys rush around the place and do a pretty skimpy test. They were rushed and there was just not enough time to really look for leaks and get a good idea what was going on with airflows and leaks.
Then the written report never came through in spite of several phone calls.

This home made blower door will cost a tenth of what I paid for my useless test, and it will tell me a lot more about whats going on, and it will tell me if the leak sealing I do actually has a positive effect, and which leaks were most significant. I think there is real value in having the blower door available over the full time you are working on leaks -- that could be months working on it a bit at a time.

They tend to make the whole blower door thing out to be rocket science, but its very simple stuff, and the furnace blower based blower door only took a couple hours to build. Figuring out how to calibrate it took a while, but only one person has to do that.

Gary

 

[kingquad]

Do you guys think that the orange Great Stuff will do a safe job around the chimney? It's not used for the woodstove. It's used for the NG boiler and traditional fireplace. I doubt that even when the NG boiler is on it gets hot. Other than that I don't know what could be used to seal the space around the chimney. I have kaowool I can stuff in the crack, but it certainly won't stop the air from moving.

Matt

Use metal flashing and fire rated silicon caulking to seal the space around your chimney. I wouldn't trust foam. I think there are some free articles over on finehomebuilding on how to do this.