Would partial air sealing cause a larger problem?


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Old 03-20-11, 11:45 AM
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Would partial air sealing cause a larger problem?

So, I had a home energy audit done the other week and got the results. I live in a 4 story interior townhouse, no attic (4th floor bedroom is in the trusses, only drywall, roof truss, and then shingles above).

They said a house my size (2000 SF) leaks on average about 1600 CFM. Mine clocked in at about 3100 CFM. Some of the main problems were leakage at the top of the party walls on the 4th floor and along the foundation on the first floor.

My questions is, the first floor leaks are fairly easy to seal (other than the direct vent fireplace, but still doable). The leaks at the top of the party walls are much more difficult since there is no attic, therefore no attic access. I would have to tear out an extensive amount of drywall to seal these gaps.

So, if I just start air sealing at the bottom of the house, how could this affect the "stack effect"? Would the neutral pressure plane rise, therefore creating a larger negative pressure area within the house? Since the furnace and water heater are on the first floor (I presume in the negative pressure plane already), I am concerned about increasing the negative pressure plane more and possibly creating a backdraft situation. The auditor stated that the stack effect is why my first floor is so cold in the winter and the 4th floor is so hot in the summer.

And what about make up air? I doubt I am going to be sealing enough to reduce my leakage from 3100 CFM to 1600 CFM,but also don't want to make the air unhealthy or need to install a fresh air system.

Thanks for your thoughts/experience,
Neil
 
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Old 03-20-11, 12:48 PM
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Hi Neil, did they take/give you any Infrared pictures to identify better where those leaks are?
Did they test just your unit or did they take readings in those adjacent homes?

Quantifying the leakage to outside vs leakage to adjacent spaces is important since adjacent units will/may have a similar stack effect and thus the measured loss to those units at -50 pascals will not reflect the real world. Plus air that leaks in from those units is hopefully conditioned.

Leakage to and from the outside is your priority for energy concerns. Leakage to adjacent units deals more with noise and indoor air quality, like smoking and non-smoking. Generally, inside units should perform much better than end units, so I question their total leakage number and their suggested normal leakage number.

As for addressing the leakage you can get to, go for it, as sealing a straw at either end will stop the flow through it. Yes, your neutral plane may shift, but it shifts up and down with the wind anyway and doubtful you have an abnormally large opening located uniquely right at that level. ie, you can theoretically open a window at the neutral plane and minimal air will go in or out, but you don't have any undiscovered open windows, we hope.

The magnitude of stack effect is determined more by those 4 floors and less so by the amount of leakage. That said, you still need to be sure combustion appliances have access to adequate amounts of combustion air in the presence of all other competing appliances, ie the worst case scenario.

When they say the top of the party walls, was that air leaking in (under a negative pressure), or an indication of cold from an IR camera. All exterior top plates will show cold, but that is not always an indication of air leakage.

I can go on far too long so one more pointer. If you are looking for a hole that is responsible for 1,000cfm or more, that isn't going to be a nail hole. Plumbing access under counters, drop ceilings over kitchen cabinets, vent pipes from basement to attic, porch overhangs, and more. Here is a link from efficiency Vermont illustrating many of the leakage paths you should check for, it opens slow. More questions welcome.
http://www.efficiencyvermont.com/ste...ide_062507.pdf

Bud
 
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Old 03-20-11, 01:16 PM
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Bud,
Thanks for the reply. I actually have that document downloaded both at work and at home and have reviewed it several times. I used it to point out some areas of concern when they came and audited the house (like my second story bay window, second floor living room over the porch and garage, etc.).

They did take IR pictures while the blower door was installed and got the reading from inside my unit.

As far as I know, no open windows Even had all new windows installed on the front and grabbed the Fed tax credit a couple of years ago. Two window seals had failed and condensation/fog was building up in between the panes. But my direct vent fireplace with bump out leaks air like a seive. I think I will be taking it apart from the outside this summer and re-building it. I don't think it was air sealed/insulated correctly when it was built.

Here is one of the pics that they took. It is in the 4th floor ceiling at the top of the party wall:



Not the best pic since I am trying to copy/paste from the PDF they emailed me, but hopefully you get the idea. It also seems that I have good leakage from the dropped ceiling in the 4th floor ceiling (tray ceiling in the roof trusses) as seen here:



I don't think that this area connects to another unit since I have a regular peaked roof with large dormers front and rear (but the attic spaces may connect or be adjacent to each other).

So, once I air seal, how can I determine if I have my combustion appliances have enough combustion air? The company will come out after I have done some/all of the repairs and re-test the house for a smaller fee (about 1/2 the original fee) to document the improvements.


Thanks,
Neil
 
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Old 03-20-11, 05:36 PM
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It's not scientific, but you can get an idea as to how much change you have made by running all fans, dryer, et al, with one downstairs window slightly open. With all of the air going out, replacement air has to come in through those leaks and your open window. As the leaks get sealed, the flow through the window will increase. An example was a very tight house with a whole house fan in the ceiling. With everything closed up, the fan just made a moaning sound trying to push air into the attic. Crack a window and the curtain wouls stand out 3' from the wall. The idea is to look for physical symptoms where you can judge the change. A bit easier for me having seen the before and after effects.

If you feel you have made good progress, it would be good to have them check the combustion air and total leakage.

If you turn on all exhaust fans and maybe add a window fan or two, you can create your own negative pressure. Then use a smoke pencil (toy smoke) or incense stick to check each area before and after your sealing efforts.

As for those walls, caulk the floor if you can and cover all electrical boxes with contact paper trimmed to fit around the device and behind the cover plate. That seals the path to the areas where you are seeing the cold in the pictures.

Bud
 
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Old 04-15-11, 11:59 AM
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You need to deal with the furnace and water heater.
Best practice is to have balanced flue appliances.

The way to deal with this is to put these items in airtight boxes, with at least 4 inch pipes joining the boxes to the outside air (measure the diameter of the exhaust pipes to get the size.) These ventilation pipes can go up, down or sideways, direction doesn't matter.

The fireplace should have its own air supply terminating as close to the fire as possible, again look at the flues and find appropriate pipes or pipes. Being able to close the cold air source and the chimney when the fire is not in use is a good idea.

Boxing in the stairs to the second floor and adding a door, will keep more of your heat downstairs.

This will remove a lot of drafts, slow the air movement and make the place cheaper to heat.

Once these large items are dealt with then proceed with the other cracks and holes.

As mentioned elsewhere, warm air rises this air is replaced by cold air pulled from outside, constantly heating this new air is expensive.
At the moment you have a cold first floor, take a careful look at the floor, fill all the cracks and gaps in and round the floor, add polystyrene insulation between the joists to reduce the heat loss down through the floor by radiation and conduction and convection. If you have access to the bottom of the joists cover the whole of the underneath with tightly butted polystyrene sheets at least three inches thick to stop the heat loss by conduction through the joists.
 
 

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