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Can A House Be Sealed Too Tight?

Post in 'The Green Room' started by fdegree, Dec 28, 2010.

  1. fdegree

    fdegree Feeling the Heat

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    I have read some individual posts recently that mentioned sealing the house tighter for various reasons. So, I thought I would start a new topic about this and share some of my thoughts.

    Personally, I think a building, of any kind, where people congregate, can be sealed too tight. In fact, there is a condition called Sick Building Syndrome that is the direct result of insufficient fresh air. This lack of fresh air impacts the Indoor Air Quality (IAQ). Without fresh air, the building will accumulate various harmful "things" floating around in the air that the people are breathing. Some of these harmful "things" are aerosols, noncombustibles from an open flame, animals exhaling CO2, fumes from cleaning products, mold, etc., etc., etc. Without the ability to purge the air in the building, and introduce fresh air, these "things" just continue to build-up. People can become quite sick from inhaling those harmful "things"...hence the term Sick Building Syndrome.

    Since we are all heating our homes with wood, lets bring this discussion down to just homes. I do believe there should be a reasonable effort to insulate and seal a home for energy conservation reasons and comfort purposes. But, I believe this can be taken too far. If the home is sealed too tight, there becomes a need for an outside air kit (OAK) on the wood stove...this OAK is not a bad thing, there are some benefits to having this installed, regardless of the tightness of the home...so please don't think I'm opposed to OAK, I'm not. But, if your home is sealed so tight that the stove won't operate properly without the OAK, it may just be sealed too tight.

    If a home is sealed too tight, there must be a means of introducing fresh air into the home for healthy IAQ purposes. This must be done mechanically...either by ducting outside air through an air handler and blowing it throughout the home...or by utilizing an energy recovery ventilator (ERV) which exhausts air from inside the home to outside, while bringing outside air in to replace that which was exhausted (there is more to these machines, but not pertinent to this discussion).

    I guess the question is:
    Which is best...natural leakage in the home or mechanically controlled fresh air?

    Each has its own set problems:
    Natural leakage is uncontrollable and unpredictable...wind can make it worse.
    Mechanical control can be costly to install, set-up, maintain and continuously operate...there will be a need for professional testing to ensure there is adequate fresh air while ensuring it is not excessive.

    I know, everyone has enough to worry about...I should be disciplined for adding to it. [​IMG]

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  2. LLigetfa

    LLigetfa Minister of Fire

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    I cannot speak for all areas of jurisdiction but in mine at least, a HRV or ERV is a code requirement on any new constuction so it makes your debate mostly moot. It is far less likely that a renovation would make a house tight enough to require a HRV/ERV retrofit.

    As for what's better, IMHO air tightness and a HRV/ERV is. Uncontrolled leakage (egress) can result in indoor humidity condensing in the structure on the way out resulting in mold and rot. It has been said that a single leaking electrical outlet can dump 5 gallons of water into the wall cavity over the course of the heating season.
  3. fdegree

    fdegree Feeling the Heat

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    Perhaps I should have been a bit clearer. I was mainly addressing the attempt at sealing a preexisting structure.

    A new home that has accounted for the "excessive" tightness by adding the mechanical ventilation certainly does NOT apply to my statements.

    I do wonder if the addition of mechanical ventilation is worth the effort and expense in existing homes if they ever become too tight?
  4. LLigetfa

    LLigetfa Minister of Fire

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    This is a bit of an odd (mis)statement and I have doubts this could ever truly manifest if you take other competing consumers of air out of the equation. The "may just be sealed too tight" portion of the statement should read as "insufficient make-up air to satisfy competing consumers".

    The more likely scenario is that other appliances create a negative pressure and that there is simply a lack of make-up air. Adding an OAK to the stove in an attempt to mitigate the negative pressure could be a mistake if the negative pressure situation persists. The building air requirements need to managed on the whole and make-up air provided for each appliance that takes away air.

    The only appliances a HRV/ERV would/could replace are exhaust fans. A dedicated OAK on a wood stove would be zero gain/loss to the building on the whole as would be a direct vent water heater or furnace that has dedicated outside air. The only appliance I have never seen to provide an outside air option is a clother dryer.
  5. snowleopard

    snowleopard Minister of Fire

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    One of the reasons that I put in a woodstove was to help with air turnover. Yes, houses can be too tight, and mine would have benefitted from an HRV system because of the high humidity levels. I decided to take it a step at a time and put the stove in and see what the needs were at that point. An HRV would be nice to have (esp. since the one I'm looking at can be modified to filter woodsmoke in the summer, which can get very bad). However, it's just not in my budget at this time.

    As far as I'm concerned (and I haven't seen the super-cold weather yet, so this could change), the stove is helping draw in fresh air from outside and dry out the interior air. It's drawing it in (I can feel the faint draft) from under the upstairs door, which is right above the stairs, so air flows down the stairs, across the dining room floor, and to the stove. It's not sufficient to affect the comfort level, doesn't lead to cold toes--I think it's just what I needed. A bit rinky-dink, far-from-elegant solution, but fully functional.

    I discussed the idea of an OAK with the installer, and he said he could put one in, but suggested waiting and seeing if there was truly a need, that he'd seen them turn into problems because of icing up.

    So far, so good. Not seeing the condensation on the windows I have in previous years. It *feels* good in here when the fire is going, and I think that's a synergy of a lot of factors, including, no doubt, sufficient oxygen.
  6. Mad Tom

    Mad Tom Member

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    If you have an older home it is a good idea to run around with some caulk and foam and seal her up. You will never get everything so you probably won't have a problem with insufficient air. It's not bad having some fresh air leaking in here and there. I think you need to find a balance. A friend of mine remodeled his home and blew foam insulation everywhere. It's like living in a Playmate cooler. He heats his house with an outside unit and keeps the heat at 85. I think it's a bit unhealthy. After 2 years he had warping in his new floors and rot around his windows. I suggested a heat exchanger to bring in fresh air, but he said he didn't need it. Oh well.
  7. Hanko

    Hanko Minister of Fire

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    Huh!!! where do you guys come up with this stuff
  8. fdegree

    fdegree Feeling the Heat

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    You make a valid point that certainly warrants attention, but you are going off in a direction that I had not intended to go. Yet, it certainly is worth discussing and putting into the equation. These things play a roll in the issue as whole. I have seen ERV's that provide more supply air into the building than is being exhausted...this could compensate for your scenario...it also places the building in a slight positive pressure, which is most desirable. This way, all air entering the building is controllable, predictable, filtered and conditioned. Hopefully, it will also provide enough fresh air to maintain healthy IAQ, which is the main issue I'm addressing here.

    My main concern is the health of the occupants. I am concerned with an existing home becoming too tight, and the owner not being aware of the potential health risks associated with the "weatherizing" efforts. If there is not enough ventilation to counteract the potential poor IAQ, the occupants may become sick periodically and never know why. This is not a good thing, and people should be aware of the potential problem.
  9. wkpoor

    wkpoor Minister of Fire

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    I'm considering an HRV as my house has high humidity even with the stove heating my house full time. Windows sweat profusely anytime the temp goes into the 20's or below. Also my house is covered with a clear moisture barrier underneath the drywall. I'm told that can be a problem.
  10. fdegree

    fdegree Feeling the Heat

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    Unfortunately, I see it much too often on a commercial level. Commercial buildings were being constructed so tight they couldn't breathe. Employees were becoming sick due to poor IAQ because there was not enough fresh air coming into the building. Once these employees found out why they were getting sick, they would file a lawsuit against the company, and usually win. Soon after, fresh air requirements were established to counter this problem. Commercial buildings were being designed to bring fresh air in through the HVAC equipment...a balance had to be established to ensure there was adequate fresh air, but not too much.

    Perhaps I'm making an issue over nothing...my experience is strictly on a commercial level, I don't work in a residential environment. But, it appears to me the risk, on a residential level, is real...sealing a home so tight it can't breath. If this occurs, forcing fresh air into the home mechanically will become a necessity in order to maintain healthy IAQ.
  11. nate379

    nate379 Guest

    Talking about vapor barrier? That is a requirement, not sure who told it that having it would be a "problem" but they are ill informed or you didn't understand quite right.

  12. nate379

    nate379 Guest

    As far as the topic, HRV/ERV is becoming a requirment.

    I wish I had one in my home, but after I bought it (new home) I only then found out about them and a retrofit was not practical.

    What my home, which is sealed VERY tight uses is the bath fans. The fans in 2 bathrooms have a humidistat which I can adjust and it will kick the fans on when needed. The makeup air comes from a vent in an interior wall which has the top plate openened up and a couple 2" PVC pipes run into that feed into the attic. Attic of course is vented through the soffit and ridge vents.
  13. coolidge

    coolidge Member

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    If you go around and look at the 100 year old houses(mine) you will see there is no soffit vents or gable end vents to vent the house. There was not any insulation until fiberjunk came around and needed venting to stay dry. I did alot of remodeling to my "old shack" in the past two years. This spring we had an energy audit done to see exactly where the next project was going to be. Blower door reading of 5120 cfm. This was after half of the house was sprayfoamed. Could you image what this house was leaking before the foam.So i did the other half and reduced the reading to 1234 cfm. Now the building is too tight, installed an HRV with a HEPA filter best money i ever spent. Fresh air all the time. So yes remodeling can make a house too tight.
  14. semipro

    semipro Minister of Fire

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    My preference would be that my house would be airtight and that I could control what exits and enters it whether air, bugs, snakes, people, whatever. I keep working to seal the holes in our house and keep finding critters making there way in. While the pests are a nuisance, to me they are just an indication that my house still has way too many holes in it. (A wasp that entered though one of my ceiling light fixtures stung me in bed just last week). Air that enters a house through unintended openings has a way of causing (water) damage and decreasing energy efficiency while introducing contamination into a home.

    In a perfect world I'd have:
    - an airtight house envelop
    - outside air supplied to combustion heating devices
    - an ERV with filtration
    - all non-combustion venting fans exiting through the ERV (bathroom, stove top, clothes dryer?)
  15. wkpoor

    wkpoor Minister of Fire

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    The more people I talk to the more I'm connecting the dots with sweaty windows and moisture barrier. Seems the houses with this problem always have the barrier.
  16. branchburner

    branchburner Minister of Fire

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    Our IAQ is much improved now that we are 100% wood heat and 0% forced hot air. The whole family was often sick, now very few colds at all. Since wood is "free" for me, I have no plans to change the fact that my old house is somewhat leaky. I agree that there is a health benefit with a certain number of air exchanges - I have no idea what the number is, but I will error on the high side.
  17. Renovation

    Renovation New Member

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    Hey WKP,

    Wet windows in cold weather can be more a symptom of cold windows than humid air. What sort of windows do you have, and do you know their R (or U) value?

    What is your concern with your vapor barrier? Generally, they should be on the warm side of the insulation, to keep water from condensing in your insulation. Unless you cool more than heat, yours is on the correct side.

    I don't want to leave FD hanging (har), so I'll vote for mechanical. I'd love to have a house so tight that I could choose my rate of air exchange--worst case I could just crack a window.
  18. fdegree

    fdegree Feeling the Heat

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    I am happy to see that some of you are verifying my suspicion...it is possible to make an existing house too tight. Nothing wrong with that, if you are prepared to add mechanical means of introducing fresh air, and ensuring it is set properly...not too much, not too little.

    I just don't want to see folks solve one problem only to create another. Understand the risks, and resolutions...then decide what is best for your situation.
  19. Renovation

    Renovation New Member

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    Thanks FD. Knowledge is a good thing, and never refuse information.

    Like Semipro, I'll be thrilled when insects (flies, hornets, ladybugs) can no longer get in my, and I have to worry about fresh air! Ironically, the 100 year old portion of my house is relatively tight, except for openings--it's the 1979 addition that's built like a shanty.
  20. woodchip

    woodchip Minister of Fire

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    New houses here are now pressure tested to ensure there are no air leaks whatsoever. None are fitted with woodburners, and as far as I'm concerned, these are not homes to live any sort of life in, they are merely statistical successes in the quest for the perfectly insulated home in some designers computer programme.

    The main problem with no natural ventilation to me is that all activities in the home produce moisture, which has to go somewhere. Breathing produces moisture, cooking produces moisture, and daring to wash in hot water produces moisture. So this will all and up condensing on the coldest surface, usually behind a wardrobe in an unoccupied bedroom which will reveal itself as a mouldy damp patch. Over here, I get so frustrated because so much money is then spent solving the damp problems (the cynic in me suspects that it is all part of the con to sap money out of hard working homeowners)...........

    Such is the problem, that when you have a woodburner installed here, anything over 18000 btu's and you need a dedicated non motorised vent whether you live in a draughty old house or a new sealed box. In an ideal situation, I would probably have a woodburner which had it's own outside air supply to avoid draughts, but having lived with an open log fire for 25 years and only switched to a woodburner a couple of months ago, I am amazed at how little air actually gets used by the woodburner. In the old days, there used to be a constant gale rushing into our lounge and up the chimney (no surprise our house was always cold), but now, I reckon the inlet for the air supply is under a square inch when open fully.

    The saddest result of sealed building are ones like this, and it really is a tragedy, nobody really realised the consequences of what they were doing, and there was probably no working CO alarm.........:

    http://www.miamiherald.com/2010/12/27/1990869/deadly-fumes-suspected-in-5-teens.html
  21. begreen

    begreen Mooderator Staff Member

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    It's definitely possible to make the house envelope very tight. So much so that gases and moisture from synthetics, humans, pets, cooking, etc. accumulate to potentially bad levels. Fortunately there are good and easy solutions. The stove should get an OAK as should the furnace or gas/oil hw heater. For fresh air, there are excellent air-to-air heat exchangers that preheat incoming makeup air with scavenged heat from the outgoing exhaust air. These can work quite well at maintaining heating efficiency. If the power goes out, the solution can be as simple as making the house "leaky" by opening a couple windows a little bit.

    There are many excellent articles on lower energy building at www.BuildingScience.com.

    http://www.buildingscience.com/resources/low-energy-bldgs
  22. woodgeek

    woodgeek Minister of Fire

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    Yup. When we are airsealing old houses, we need to keep an eye on combustion devices and indoor RH, and should add mechanical ventilation if/when we get below 0.5 natural air changes per hour (ACH_nat). Even at that level of tightness, one would have to crack a window in mild weather, or when you are having a party. In my case, I bought a 60s vintage 2200 sq ft house that was fully insulated top to bottom, weatherstripped carefully and had all storm windows and doors, and proceeded to blow 1000+ gals of fuel oil in the first season, versus the 400-600 I expected. At the same time, ran several humidifiers full out all winter, and never got the RH over 20%, not comfortable or 'healthy'. After a few calcs I realized that my house (airtight) would use ~400 gals, and that the other 600+ gals was air leakage, about 2.0 ACH_nat. or 6 times a new construction average.

    I have now cut that air leakage in half, saving the equivalent of 300 gals oil/yr, and a large console humidifier still only bumps my indoor RH by 4-5% at 3 gals of water/day.

    So, FD, I have to agree that houses can be made too tight, and there are horror stories out there. Frankly, however, pretty much every article I read on airsealing strongly emphasizes the importance of keeping a close eye on RH, IAQ and combustion device backdraft, just your concerns. I am much more worried about the massive energy wastage as a society and harm to human health due to air leakage in older homes (e.g. skin and respiratory conditions from low RH, outdoor allergens), and that your well-placed concerns might get in the way. There is now plenty of evidence that low RH significantly fosters the spread of flu and colds (the real reason we have a cold season).

    I think we should all care more about IAQ, and that airsealing, forced venting, and careful RH control are all important.
  23. fdegree

    fdegree Feeling the Heat

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    Excellent information...

    I have some questions:
    I understand the basics of how a blower door test works, and that the blower door test is used to calculate the ACH. Am I safe in assuming that ACH_nat. is calculated without the use of the blower door...if so, how is that calculated? Or, am I wrong and the blower door test is the ACH_nat.?

    Through the process of airsealing houses, where do you find most of the leakage coming from?
  24. woodgeek

    woodgeek Minister of Fire

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    In a blower door test (as I understand it), the house is depressurized to 50 Pa pressure (about 1 lb/sq ft), using a variable speed fan and the CFM through the fan is computed. That measured number, CFM50, can be converted to air changes per hour at 50 Pa, or ACH50. The natural ACH, ACH_nat, is estimated from the ACH50 by dividing ACH50 by 12 or 15 or 20, depending on the local climate, (degree days and wind).

    I have not had a blower door test done, (I will when I run out of obvious things to seal) but can estimate my ACH_nat from a demand budget computing from the known conductive loads (wall/attic/floor/window areas and nominal R-values), and comparing the result with my usage. This came out to an expected usage of 450 gallons oil/season, versus 1050 actual (model accounts for background heat sources equivalent to ~100 gals). I can compute from the specific heat of air and my house volume that 1 ACH_nat at typical january temps corresponds to ~33 MMBTU/yr, or that based on my excess usage (600 gals or 66 MMBTU) my initial ACH_nat when I bought my house was ~ 2. High, but not so unusual for a 60s house that has never been airsealed.

    With my recent airsealing efforts, oil usage is down to 750 (no insulation was added, only airsealing), and I have plenty more to do yet... The remaining excess demand (300 gal oil = 33 MMBTU) suggests that I still have ACH_nat ~ 1 after two years of DIY airsealing. I confirmed this using my humidifier. Repeated cycling of the humidifier shows that at 3 gal/day, I only get about a 4% steady state increase in RH (after several hours). Using a psychrometric chart and my house volume, I can compute that 25 lbs/day of water should increase my RH by 5% at ACH=1, confirming my estimate.

    There are lots of great resources on the web listing likely locations for air leakage. It can require some real sleuthing to find all the openings.

    My double hung windows were leaking because the loose locks were not compressing the metal weather stripping at the top and bottom, and I also needed to add a v-strip where the two sliding panes overlap. Shimming the locks and adding v-strip on ~15 windows took one weekend and saved me ~150 gals of oil per year.

    In the attic, I found a couple square feet of openings where the plumbing stack and masonry chimneys meet the attic, about 6 sq ft of open stud cavities between some interior walls and the attic, and roughly 150 linear feet of ~1/4" wide openings along load bearing walls and the attic floor (another 3 square feet). Playing with an IR thermometer, it seems like I have cold air rushing in under my sill plate, dispersing into the living space through my hardwood floors, and then getting into the interior walls (again through the floor) and exiting through the attic. In so many words, its equivalent to having a wide open window upstairs and downstairs (>10 sq ft), all buried in the framing or under the siding and attic insulation for 50 years. And we never felt a draft!

    And as mentioned in your OP, after every round of sealing I turn on all exhaust fans and the dryer, verify that my boiler doesn't backdraft, and have 3 CO detectors. When I get 'done' I will have a blower door test, check for radon, and probably install some mechanical ventilation (~15 cfm/person) if the house does get tight.
  25. Mcbride

    Mcbride New Member

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    [/quote]

    Excellent information...

    I have some questions:
    I understand the basics of how a blower door test works, and that the blower door test is used to calculate the ACH. Am I safe in assuming that ACH_nat. is calculated without the use of the blower door...if so, how is that calculated? Or, am I wrong and the blower door test is the ACH_nat.?

    Through the process of airsealing houses, where do you find most of the leakage coming from?[/quote]

    I have a friend that does this for a living.
    Top leaking areas according to hime are:

    Dryer vents.
    Range hood vents.
    Electrical outlets.
    light switches.
    around windows.
    around doors.
    bathroom fan vents.
    attic accesses.
    crawl space accesses.


    I think he mentioned a few others to me, but I forgot them.

    ps. those are in no particular order.

    I know in my last home purchase, the dryer and range vents were leaking a lot, and the attic access was leaking a lot.

    I replaced most of the windows and doors myself, that way I was asured they sealed as tight as possible.
    Too many contractors rush the job, and do not seal around say a window correctly.
    It takes time to do a good job.

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