When air-sealing a house, does it always make more economic sense to make the house as tight as possible and then add mechanical ventilation or to air-seal down to some building tightness limit?
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| Posted in Energy Efficiency and Durability on
I’m working for an energy efficiency retrofit program. We have a very limited budget for our houses and therefore have been air-sealing down to the Minimum Building Airflow Standard (ASHRAE 62-89) so that we don’t have the extra cost of mechanical ventilation. Is this flawed thinking? Is it usually in the economic interest of the client to air-seal as much as possible and then have the extra cost of putting in a vent fan?
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Replies
Karen,
You'll find many advocates on this forum of the hermetically-sealed house. But an appropriate answer would depend on your project goals.
If you're working in low-income communities in an attempt to improve energy efficiency and reduce utility costs for your clients, then sealing the primary leakage points down to minimum airflow standards is probably a good objective. Combine that with adding attic insulation and you've made a substantial contribution to both your clients and to the world.
The downside of using building envelope leakage to maintain indoor air quality and keep humidity within limits is that there is neither flow nor directional control, since air exchange depends on wind and stack effect pressures. But simply adding an exhaust fan won't do anything to improve infiltration control, without dedicated intake vents to direct fresh air where it's needed. And that's effective only if outside air is cleaner than inside air. In some urban areas, it's not.
Karen,
To achieve the lowest possible cost for space heating and cooling, it's necessary to seal air leaks. The tighter the home, the lower the cost of space conditioning. Period.
Of course, it does cost a little more to develop details that limit air leakage. But the energy savings over the lifetime of the building are far greater than the small incremental cost during construction of implementing these air-sealing details. It will never be cheaper to do the work than during the initial construction.
All new homes should have a mechanical ventilation system -- even those that are trying to include "just enough air leakage" to supply fresh air accidentally, through the effects of wind and the stack effect. Depending on random air leaks to supply fresh air is nuts. While you may get enough fresh air during the depths of winter, when the stack effect is greatest, or on windy days, when infiltration and exfiltration are high, what about windless days during the spring and fall? How do your occupants get fresh air on those days? (Studies show that occupants are generally very bad at determining when they should open or close their windows.)
There are a few exceptions to these principles. In San Diego or Hawaii, arguably, air tightness isn't that important.
Martin,
Karen is talking about low-budget energy retrofits on existing housing, not new construction.
No question this site advocates living inside of a glass bottle and then adding mechanical venting. I am with you Karen in enjoying home life without electric fan ventilation. I would add that the interior should be free of as much VOCs as possible, ie... no new low cost carpet, no particle board etc. If the home has occupants that never open a door or window for days at a time... maybe leave the home leaky. We have a builder here that has built tight natural interior homes for 30 years... and as far as I know all his clients are living and dieing of causes other than not having mechanical ventilation.
Remember to cut all interior doors with at least 1" air space along bottom. As to urban and or polluted air where this site is... who knows.... myself... I would move.
Martin,
If I may, your noted "arguable" point that air sealing may not be needed in place like San Diego and Hawaii is misguided. The two climates are quite different as well. The basics of understanding why air sealing is important wherever you reside has more to do with future of building and the rise of space conditioning. As the code moves toward a requirement for mechanical ventilation and homeowners have become increasingly interested in maintaining 65 to 75 degrees in their homes, the need for air sealing is ever more prevalent. There are many homes in San Diego, that run their AC continuously during cooling seasons. Air leakage in those buildings is not doing any favors to the homeowner utility bills nor it is healthy.
As Karen mentioned, sealing down to Minimum building airflow standard (ASHRAE 62-1989) will provides results, but does it meet the overall criteria of the project/program? As Mr. Riversong mentioned, the results drive in the right direction but lacks the potential health and safety benefits mechanical ventilation provides. As the code req. will move to ASHRAE-62.2-2007, that process will no longer be acceptable. Therefore even even the folks who live in San Diego will need to provide mechanical ventilation. :)
Karen, is your program for low income residents? If not, you may get participant buy-in when you can demonstrate the effectiveness of a higher lvl of air sealing and mechanical ventilation. In addition, if your program requires a HERS or BPI based audit, the report should include a Saving to Investment ratio which could help define the feasibility of expanding your program. I hope the program is a success!
Cheers,
Christian.... retrofits.... is the topic... are you saying that we are coming close to forcing the upgrade of existing homes to electric fan ventilation? I will be the first person incarcerrated for such a crime if such a law is passed. Sure... if one has AC on 24/7.... then it makes sense to have the rest... but AC on 24/7 doesn't make sense to me. I lived in Daytona FL with none... had a fan over the bed... and the windows opened lots... I have none now. I for one am not ready for living in a Jetson aged perfectly designed and conditioned space. The outdoors here is where the air is right to breath... not indoor air.
And....
Why do people choose to live where the outside air is the bad air and the inside puirfied air that is possibly screwing up people's immunity systems is thought of as good?
Unintended consequences are taking over all our new half baked ideas. such as drill baby drill.... sure.. let's drill everywhere and at every depth.... oops.... what do we do now that we fouled up an entire ocean the size of the Atlantic when all that oil gets in the Gulf Stream. Not all greed to use energy for each of us kings to have a castle is going to work out for the planets favor.
ADKJAC-
I live in CA so I am biased to our rules and code. California Energy Commission (CEC) Title 24 standards do not require the ASHRAE standard 62.2-2007 for a retrofit. Only for additions over 1000sf and new construction. This code went into effect January 1, 2010.
From a performance standpoint, air leakage contributes to reduced efficiency. Up to 40% of heat loss in some areas. Therefore reducing the leakage can lead to potential reduction in energy consumption. Energy Star, BPI, RESNET standards also encourage mechanical ventilation for energy efficiency.
Sure opening a window is great in the summer time, but mean radiant temperature in a building effects people differently and therefore some people, especially in humid climates like FL, prefer to run their AC for space conditioning (also to dehumidify). I was simply pointing out that the building will perform at a higher level when you reduce the air leakage and use mechanical ventilation. You have to look at the building as a whole system.
for more information of oil spill and retrofits check out this link:
http://www.efficiencyfirst.org/blog/2010/06/15/retrofit-baby-retrofit/
I don't disagree with the law of unintended consequence but you example is an oversimplification of the law.
Thanks for the response.
Christian...I hear yaa... do you hear me? Get rid of AC... How? Raise the cost of E high enough so people stop using it. Take that tax money and get rid of property tax and make all forms of higher education less expensive. Include education in non college course work... craftmanship, etc.
I am not for electric mechanical homes. I am for led lights that are bringing us closer to homes that use not E.
LIving in communities... song, dance, gardening, exercise (vball and skiing my favorites), beer brewing... travelling lightly on the planet... eliminating pollution... living with acceptance of our different neighbors... (exception for not enjoying... more like pestering our 400 amp neighbors)... ha haa..
I hear yaa... do you hear me?
no mechanical ventilation needed! Step outside..... crack a window for the sake of... aj
Adkjac....
Your posts... are... like... ramblings... and.... are... distractions.
Brett, I agree. It's amazing that someone with nothing useful to say can waste so many words saying it.
ADJACK, aka aj, aka Bill Robinson, aka GOD is trying to dominate this forum with his brand of nonsense and is going to drive people away.
complaining about an on topic post by attacking a poster... makes your two posts useful?
On topic... worldwide ICC uniform codes that are moving toward mandating electric fan units to clean our dirty air is not my idea of an improvement to society.
It's not fixing the problem. Pollution is the problem. Natural elements in the air from what I read are good for immunity system developement for creatures in their early years of life.
Disagree?
I can see myself using them like Robert uses foam even though he prefers not to.
I'll give it a shot at toning down my ramblings... but... less rambling gets a bit adultish. Do we have to grow up?
LOL
To bring this conversation back on topic, this program is only concerned with retrofits and it is primarily for low-income people. And this program is in Arkansas where people DO run their A/C 24/7 whether they should or not.
So what do people think? Is the cost of mechanical ventilation often offset by savings in really good air-sealing (tighter than ASHRAE 62-89)? Even if it's not, should we make it policy to air-seal as much as possible to get as much savings out of air-sealing as feasible?
Karen,
Your question is not a simple one. Low-income residents often suffer more than most from poor indoor air quality, but if they are located in polluted neighborhoods then it's not certain that outside air would be any better.
Air-sealing is often the least expensive approach to energy efficiency and it generally makes economic sense to take that as far as feasible. Without a blower door test, however, it's impossible to know just how tight a house has become, so it's reasonable to also provide for some fresh air exchange.
The least expensive way to do this would be to replace (or install) the bathroom exhaust fans with quiet, efficient Panasonic Whisper Lite models connected to a time-delay or occupant sensing switch so that they will run for several hours per day, and then provide make-up air with passive air inlets such as the American Aldes Airlet 100 located in living areas and bedrooms.
For a low income program with limited resources, you'd be better off not air sealing below your ventilation guidelines and instead spending the resources that would have gone to an exhaust fan (and makeup air inlets!) on other energy saving opportunities in the homes. The drawback to this approach is that the ventilation guideline is not some magic number and provides no guarantee of good IAQ so you should also look at pollutant sources, assess combustion safety, and make sure there are good CO and smoke detectors in the homes you work in. In terms of missed energy savings from more sealing plus ventilation -- they are likely to be tiny and not cost-effective.
Karen,
If you want to see how another state handles this issue, the Maine Weatherization protocols are available here: http://www.mainehousing.org/Documents%5CEnergy%5CEnergy-MEExStandards.pdf
Jesse Thompson
Kaplan Thompson Architects