I have read a bunch of posts by Teddy Bear about making sure to keep adequate fresh air "make up" in a home. I assume you mean, simply open a window at all times.
How do I know how many windows to keep open or if only one window, how much to open it?
I have an 1,100 square foot single story ranch home with basement.
I am under the assumption that one window open about 1/4 would do the trick, but wanted to ask the experts.
Somebody's pulling your chain.........
Originally Posted by brewyourown
Teddy Bear was conducting an experiment of how to control humidity and maintain an adequate fresh air exchange rate during cool, wet weather when the a/c system runs very little or not at all. His area of the country likely experiences a prolonged cool, wet weather season, as his posts are filled with discussion on that weather condition. It's a condition where it is not cold enough to run the furnace, but not warm enough to require a/c. In my neck of the woods those days are few and far between.
Originally Posted by brewyourown
TB's concerns appear to revolve around indoor air quality, with maintaining adequate air changes per hour when a house is occupied. Carnak, another pro member here, has offered air changes per hour being established by C02 levels vs. a fixed standard, which is an interesting notion. As more people seek to tighten up their homes to combat rising energy costs, the discussion of fresh air exchange will become more important, as modern homes typically are full of volatile organic compounds that off-gas and create indoor pollution.
Personally, I think the smarter approach is to purge as much VOC producing stuff from the home as reasonably possible, and then provide adequate ventilation for human respiration and to keep the house air from becoming stale or riddled with objectionable odors. Fresh air introduction is best if it occurs through the a/c or furnace, so it can be cooled and dehumidified in hot, humid climates, and heated/humidified in cold weather. Dry climates are easier to ventilate during hot weather, as fresh air introduction brings in little moisture.
As for the cracked window...I drive around with all my truck windows up when the a/c is on. Same for my house. Windows are closed.
A/c contractors feel that we are pulling their chain when we talk about fresh air venitilation. Most IAQ experts feel you should have enough fresh air to change the air in the home every 3-4 hours when the home is occupied. This purges indoor pollutants and renew oxygen. During cold weather the temp difference between inside and outside plus wind provides the pressure that may provide enough fresh air. During moderte weather and light winds, home do not get enough fresh air. Thank god for that lack of fresh air because if the homes did get the fresh air, they are damp or +60%RH. High humidity allows the growth of mold and dust mites. Without significant cooling load, the a/c with not remove the 30-60 lbs. of moisture from the occupants and fresh air to maintain <50%RH.
Originally Posted by brewyourown
I must confess, I lead effort to get fresh air into home and control moisture. It's the guts of IAQ. This year most home in the Midwest and the Northeast do not have significant cooling load. I have be data logging my home which unfortunately does not mechanical fresh air ventilation. I cracked a window 1" in an effort to get a little additional fresh air into my home. I does not work well. When the wind is upto 15 mph, you may get enough fresh air. When the wind does not blow, you get no fresh air. Consider a better method, a small blower mixing in 75 cfm of fresh when the home is occupied (my future). Attaching my recent data. I had about 4 hours of a/c this year and am maintaining 50%RH with a 90 pint dehumidifier in the basement. Check the %RH in the basement and on the mainfloor. We love the comfort level. Unfortunately, my water heater leaked water on the carpet in the basement bedroom. A second dehu and some box fans are maintaining 45%RH while drying the carpet.
I have VS fan a/c and operate the fan "on" slow speed. It is working well. I am using $1/day for the dehumidifier. As the weather warms, more a/c and less dehumidification results. Not sure about the fan "on" part during moderate a/c cooling loads. On a real hot day with enough cooling hours, probably no dehumidification is needed to maintain <50%RH throughout the home. Regards TB
Don't open windows, unless you had a blower door test done to comfirm that you need more fresh air.
Because of the cost (MONEY) you could end up spending to condition that air if you don't need it.
The Sear's near me. Has their fresh air intakes closed. They shut their min air intake dampers.
What they did, is put their fresh air system on a CO2 metering system. If the CO2 gets high, the dampers open 100%. Once it drops to normal levels they shut 100% again.
They have reduced their A/C cost by 40%.
If you want to install mechanical ventalion, fine. If you want to leave a window open, fine.
If you want to save money, find out if you need i first.
Most older construction homes have more then enough natural infiltration, that extra venting is not needed.
If you need to get fresh air in the home, then you want the air to enter though the unit so it is conditioned once in the living space. In high humid areas, an open window with the right conditions can cause water to start running down the walls and making everything damp...I have seen it before. Green and black are not pretty sights on the walls, carpet etc.
In the dead of winter, most homes get enough fresh air. I monitored the 30 sqin. open space of the window. During light winds, very little fresh air entered the opening except during wind. The idea of monitoring CO2 has some flaws. With five people in a home a CO2 monitor to activate mechanical ventilation to purge indoor pollutants is expensive but works. When one person is in a typical home, one will not trigger the ventilation system even though the indoor pollutants are high. I is safer and simpler to provide fresh air when the home is occupied by even one person particularly during the summer season. The minimum air change rate per hour(ach) suggested is .2-.3 ach. This is 50-75 cubic feet per minute (cfm). Mechanically provide fresh air when occupied should be done by a fan that is econimical to operate when the house is occupied. The large a/c blower or matching window openings/wind speed is not practical to provide the ideal small steady flow of fresh air needed. When damp outside, minimal fresh air has 1-2 lbs. of excess moissture per hour. During cold dry weather (below 50^F), fresh purges moisture from the home. If you are in your home 12 hours per day and have minimal fresh air, figure on dehumidifying 30-50 lbs. of moisture per day to maintain <50%RH. A properly functioning a/c needs many hours of steady operation each day to remove that much moisture. Eliminating much needed fresh ventilation reduces the moisture load. From limited testiing, using a whole house dehumidifier to control moisture is more practical than overcooling the home. In an air tight home, the dehu can also provide fresh air when the home is occupied. Maybe a little more than what you wanted, but dehus provide <50%RH even with a over-sized a/c at a minimal operating cost. For similar cost as a full featured a/c, perfect humidity control and IAQ can be provided with a high SEER a/c and whole house dehu. Regards TB
Originally Posted by beenthere
thanks guys, great advice and some really interesting insight in this thread. I am going to leave the windows closed :)
I have an older home so I am sure that air is coming in somewhere or another.
Great forum you guys have here, I hope that the questions I have been asking are what it's about, if not, I apologize.
I would like to learn more about hvac so I don't make the same mistakes in the future.
In an air tight home, the dehu can also provide fresh air when the home is occupied. Maybe a little more than what you wanted,
We weren't talking about a tight house here.
The house will tell you in winter time if there is a lack of fresh air as there will be a window condensation problem. A dry house is a drafty house. When I was upgrading furnaces on a home 30 plus years old, I would look to see if they were running a humidifier or not. This would tell me that I better add some mechanical ventialtion and it also gave me an idea of what kind of infiltration value to use when szing up a replacement furnace. A draft hood furnace was quite a ventilator.
Now as far as summer time goes, if you do not have air conditioning, feel free to leave all your windows open, you will not have any surfaces cool enough to get condensation BUT your home will be a lot more uncomfortable than your next door neighbour who kept his windows closed and his drapes drawn shut.
When you have central air conditioning, you can ventilate intermittently, you just do it at a higher rate than if you did it continuosly. You do not need CO2 controls to do this. Just draw in fresh air to the return side of your system when the compressor is running and treat this air before it goes into the space.
I would say the only situations where you are forced to constantly pump in untreated outside air directly to the space is when your sufer from a condition known as dehusalesitis
From my own experience, I am finding that looking at the CO2 levels inside homes gives me a way of determining the "natural ventilation" rate of the home or building. By natural ventilation I am refering to infiltration and the way people usually use their home such as running fans in the bathroom, drying clothes, range hoods, a fresh air intake to the return duct etc. You can verify if the home already has more than engough fresh air moving through it, and I am talking in the summer time.
A test some of you can try, especially if you use ceiling diffusers.
With the air conditioning running, open a door that is not lined up with a prevailing wind if possible. See if you feel cold air falling out by gravity along the bottom of the door way and hot air rushing in at the top of the door opening. This is an inverted stack, cold air is falling down to the floor and pressurizing the lower level, exactly opposite to how warm air rises up inside a home in winter and pushes on the ceiling openings and around the upstairs window frames above the neutral plane.
After your blower door test if you need fresh air, I would say to use a mechanical ventilater that can be adjusted to open for a certain amount of times per day. The blower door test will tell you how to set it.