# Can A House Be Sealed Too Tight?



## fdegree (Dec 28, 2010)

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.


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## LLigetfa (Dec 28, 2010)

fdegree said:
			
		

> 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?


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.


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## fdegree (Dec 28, 2010)

LLigetfa said:
			
		

> 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.



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?


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## LLigetfa (Dec 28, 2010)

fdegree said:
			
		

> 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.


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.


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## snowleopard (Dec 28, 2010)

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.


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## Mad Tom (Dec 28, 2010)

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.


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## Hanko (Dec 28, 2010)

fdegree said:
			
		

> 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.
> 
> ...



Huh where do you guys come up with this stuff


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## fdegree (Dec 28, 2010)

LLigetfa said:
			
		

> fdegree said:
> 
> 
> 
> ...



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.


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## wkpoor (Dec 28, 2010)

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.


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## fdegree (Dec 28, 2010)

Hanko said:
			
		

> Huh where do you guys come up with this stuff



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.


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## nate379 (Dec 28, 2010)

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.



			
				wkpoor said:
			
		

> my house is covered with a clear moisture barrier underneath the drywall. I'm told that can be a problem.


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## nate379 (Dec 28, 2010)

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.


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## coolidge (Dec 28, 2010)

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.


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## semipro (Dec 28, 2010)

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?)


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## wkpoor (Dec 28, 2010)

NATE379 said:
			
		

> 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.
> 
> 
> 
> ...


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.


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## branchburner (Dec 28, 2010)

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.


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## Renovation (Dec 28, 2010)

wkpoor said:
			
		

> 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.



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.


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## fdegree (Dec 28, 2010)

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.


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## Renovation (Dec 28, 2010)

fdegree said:
			
		

> 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.



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.


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## woodchip (Dec 28, 2010)

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


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## begreen (Dec 28, 2010)

fdegree said:
			
		

> 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.



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


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## woodgeek (Dec 29, 2010)

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.


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## fdegree (Dec 29, 2010)

woodgeek said:
			
		

> 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.
> 
> ...



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?


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## woodgeek (Dec 29, 2010)

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.


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## Mcbride (Dec 29, 2010)

[/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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## DBoon (Dec 30, 2010)

I have an older 1920's house.  Short of tearing down all the plaster and starting over again, I'm not sure that there is too much you can do to stop air infiltration.  I've done a lot, and it has helped a lot, but the house still "breathes" plenty well as far as I can tell - no lingering cooking odors, no excess humidity, etc.  

McBride - great list, it's giving me some things to think about. 

I've done the following on my older home:

1. Installed foam covers on all outside wall outlet and switch covers
2. Insulated outside walls with blown-in fiberglass (all interior walls are plaster with wallpaper over them, so there is not much moisture migration, I believe)
3. Sealed attic penetrations (there weren't many)
4. Insulated the attic hatch with foam board and sealed the edges with EPDM weatherstrip
5. Insulated the bottom edge of the double hung window with EPDM weatherstrip
6. Weatherstripped the sides of the double hung windows with sprung bronze
7. Caulked all of the floor penetrations with fire stop caulk
8. Insulated the above ground basement walls with 2" of spray on foam
9. Caulked the joint between the sill and the top plate with silicone caulk

I've probably done a few other things that don't come to mind right now.  

So, to the point of the original poster, I wouldn't be too concerned about weatherizing an older house - there is not enough you can do to ever tighten it up too much without extreme renovations.  For a newer house, I wouldn't be too concerned either unless you knew the builder and all contractors were trained in building a tight house.  Otherwise, they will leave lots of opportunities for infiltration either through ignorance or neglect.  

For commercial buildings - perhaps a different story.  In that case, often there are inoperable windows and a tighter building envelope.


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## benjamin (Dec 31, 2010)

Woodgeek, thanks for the info relating ACH50 to ACH nat.

I say it is theoretically possible to make an old house too tight, but in most cases it's like telling a morbidly obese man to cut back on the calories and at the same time worrying that he will die of starvation.  

New houses deal with fresh air, and any house that is completely redone should be treated like new construction, but the typical old house has so much leakage that it will never get to a dangerously low level of air leakage without adding an entire new surface to the inside or outside.  Even with a completely sealed building envelope, most chimney are leaking enough air past the damper to maintain air quality inside.


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## ihookem (Jan 3, 2011)

Dboon, # 8 did the most but everything helps. My 1 year old  home is  so air tight it ain't funny. 4" foam in the walls, r 60 ceiling. Everything is sealed very tight. I even have storms on a new all brick home. I don't believe a house can be too air tight. I believe the walls and ceilings should be encapsulated so no air infilterates the walls. Make sure it's dry when building. If you have a house like this you need to do things mom and dad never had to do.  You can get an air exchange for 1,000 bucks. This helps. I am cheap and don't think it's worth it. When it's cold like 30F or less I open every window and door in the house. When I'm done I shut the first opening, then go along and shut them all If it's calm I wait a few minutes then shut them. An easy way to tell is sweaty windows. This also gives fresh air daily, keeps dust down too. My RH shouldn't get more than 50% if under 35*, 45% if it's 25* and if it's cold like below 0 It should be no more than 40% or so. It varies but moisure on the windows tells me it's too damp. If it's real damp outsied I may wait a day. It seem summer builds moisture so fall is when I can open the door on a dry morning and see the moisture leave the house. It is to some degree an air tight house to open the windows but I'm sure it still saves energy. If ya got sweaty windows put on storms, it reduces moisture 50% on the inside glass. A moist house is very comfy though.


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## midwestcoast (Jan 5, 2011)

I'm with the crowd that say "Yes, houses can be made too tight through renovation work" and "No, it is not likely unless the whole house is overhauled". As prev stated the biggest concern after doing very significant air-sealing in an older home is checking for any backdrafting in open-venting combustion appliances (like water heaters, low efficiency furnaces...).  Getting an older home sealed-up to the point where things like moisture, off-gassing & cooking emissions are a real problem is VERY difficult. Many leaks are often hidden behind finishes & those will be very tough to seal.
As for newer homes, controlled ventilation is becoming the norm & I'd way rather have an ERV or HRV bringing in conditioned fresh air where & when needed than feel cold drafts on a windy day & have a stuffy house on a calm day. Saves energy too.


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## jimbom (Jan 15, 2011)

I built my house very air tight from the beginning.  I foamed every penetration in every location in the house interior and exterior.  All fixtures.  Everything.  Now, I am in control of the air and vapor that enters my house.  I supply a lot of outside air, but it comes in where I want.  Direct to the mechanical space in the basement.  Direct to the dryer.  To a fireplace that we never use.  Makeup for the exhaust fans comes up from the basement.  All from always open exterior supply entries through insulated flex duct so I have no condensation.  So far in twenty years, it has worked well.  I am sure I could squeeze a few more btu out of the in/out exchange, but never enough to meet economic payback criteria.


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## ccwhite (Feb 1, 2011)

LLigetfa said:
			
		

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Well said. You beat me to it. Seal as tight as possible and control your fresh air with an HRV/ERV. Rather than uncontrolled airflow.


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## pyper (Feb 1, 2011)

wkpoor said:
			
		

> 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.



It definitely _can_ be a problem, especially if it isn't done correctly.

The higher your humidity and the warmer your climate, the more likely you are to have a problem. Here in the south the backing on insulation is all the vapor retarder that you want. I don't know about Ohio.

In North Carolina 15 or so years ago they started requiring builders of apartments under a certain government program to build very tight, including a plastic vapor barrier. A few years later, they started getting massive mold problems in these units. They didn't have HRV/ERV in them, so the water vapor was just accumulating in the buildings and mold started growing on the paper on the back of the drywall.

If you have an old house you probably *can't* make it too tight -- there are just too many paths out.

I can see some real benefits to HRV/ERV, but what happens when the power goes out?


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## woodgeek (Feb 1, 2011)

pyper said:
			
		

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you open a window


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## ccwhite (Feb 1, 2011)

pyper said:
			
		

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Nothing. You won't accumulate enough moisture to be a problem during a power outage. The hrv won't do anything without power it has its own fan. (no real air leak) When the power is back on the hrv will be too.


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## SandManConservation (Feb 2, 2011)

I think I heard that indoor air is almost always dirties than out door air, sealed or not. Is that true?


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## ccwhite (Feb 2, 2011)

SandManConservation said:
			
		

> I think I heard that indoor air is almost always dirties than out door air, sealed or not. Is that true?



Welcome to the forums sandman. I don't think this could be true. We are constantly recirculating and filtering our indoor air. I guess you could live somewhere where the outside air is exceptionally pristine. I don't know.


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## Alan Gage (Feb 2, 2011)

SandManConservation said:
			
		

> I think I heard that indoor air is almost always dirties than out door air, sealed or not. Is that true?



Sounds right to me. All the air inside your home has to come from the outside so it all starts out the same. It's not cleaned up at all, at least in most houses, before it gets inside. The longer it's in the house the more "contaminants" it's going to pick up from everything that goes on in the house from cooking in the kitchen, out gassing from some materials, to people breathing and probably lots of other things. 

Alan


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## semipro (Feb 2, 2011)

SandManConservation said:
			
		

> I think I heard that indoor air is almost always dirties than out door air, sealed or not. Is that true?



I'm pretty sure this depends on what your contaminant of interest is.  If its formaldehyde or some other  material out-gassing from construction materials (plywood, carpet, paint) then its likely indoor air is dirtier.  If you're talking pollen, soot, mercury, ozone, or airborne soil, then outside air is probably dirtier.


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## Alan Gage (Feb 2, 2011)

Semipro said:
			
		

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You're right. It would also depend on the house. In my house I have no forced air heating/cooling and no filtering of any kind. So anything that's outside is inside too. Plus anything that I add to the mix. If the air is cleaner when it leaves my house than when it came in it's because it left any contaminants (pollen, dirt, dust) behind in my house.

Alan


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## henkmeuzelaar (Feb 2, 2011)

Semipro said:
			
		

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Agree with both comments.

Two big indoor air quality problems common to many houses are: 
(1) VOCs (volatile organic hydrocarbons) coming from the garage, because of gasoline containers/tanks, as well as solvent, paint and other coatings stored, used and spilled there; and 

(2) fine dust stirred up by moving around, vacuum cleaning, making the beds, faulty driers and stoves, etc. 

And, of course, cutting lumber (or am I the only one running his radial saw in the living room when it gets too cold on the porch??  )

Henk


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## begreen (Feb 3, 2011)

I suspect you may be the only married guy that does this.


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## marcomjl (Oct 28, 2011)

Sorry to bring up an old post but wanted to address some questions and ideas.

New construction planned or old home remolded planning to tighten up the home with spray insulation and preventing any air leaks is very beneficial.  But like anything doing this causes sickness in the air of the home since it can't breathe you'd want to install a simple air exchanger and that solves the issue.  Not only is the home super insulated but can exchange the old air for fresh clean air.


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## begreen (Oct 28, 2011)

Old house or new, a heat recovery ventilator makes sense once it has been greatly tightened up. It's a necessity in modern super-tight construction. 

http://www.thisoldhouse.com/toh/article/0,,212227,00.html


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