Indoor air quality discussion

[MN Renovator]

You can't have much of a party in a 324 sq ft of space. It isn't like putting 10 people in a room immediately creates an unhealthy condition. If the party lasts 3 hours than the standard is cut in half to 7.5 cfm per person. So 75 CFM for 10 people would be adequate for the short period that they are there which isn't even twice the 43.2CFM that your theoretical 18x18 foot box dictates. I have computer fans that push more than this and I'll likely have bathroom fans and kitchen exhaust fans running that will not require any additional ventilation for the house than that. Even if I had 15CFM for my needs and had 20 people in my house for a party, I'm not going to be concerned because any air contamination would take time to occur and since I don't have a party every day, cracking the window a bit and turning on a bathroom fan would be enough in such a demand ventilation requirement. AHRI used to recommend 7.5CFM per person in the 70's, I'd imagine that not every house met that mark, keep in mind a family of 5 may have been living in 1200 sq ft back then or in the preceding decades. My mother grew up in a 1000sq ft house with 5 people, so even with a leaky house, it would have probably been about that if it were reasonably built but hers seemed to be reasonably well sealed, not too many windows, two doors, single story, no attic hatch to be leaky.

Even in new houses with heat exchange ventilation, these systems are designed for the number of people expected to be in the house based on the number of bedrooms and house size with no provision for a party.

[S-F]

Have any of the people here who are advocating smaller than recommended ventilation rates spent any length of time in a house that's really tight with the HRV turned off? Like spending two days and a night.

At any rate, this is all academic as I suspect just about everyone in this thread doesn't have a house that needs mechanical ventilation. If any of the nay sayers do get their houses down to really low blower door levels you can always install the recommended size HRV and then set it on a lower speed until you realize that you feel much better running it as everyone else suggests. You run it on a lower speed at night any way.

You guys do know that you can control the speed..... Right? You install a switch on a wall somewhere. What's the problem with having the recommended size HRV? If you burn your rice and it's -10 outside you just turn up the fan instead of opening a window. Opening a window works but you loose more heat that by moving the air. Just like with cooking and bath exhaust. Sure you can just open the window in the bathroom when you shower in the winter but more heat will be lost than by moving air via a fan for the same amount of time. Personally I plan on getting one that's larger than recommended.

[AC_Hacker]

Originally Posted by MN Renovator

You can't have much of a party in a 324 sq ft of space. It isn't like putting 10 people in a room immediately creates an unhealthy condition. If the party lasts 3 hours than the standard is cut in half to 7.5 cfm per person.

I recently went to a medium-sized meeting in a tight house, no mechanical ventilation... the meeting was upstairs, cathedral ceiling. People were sitting quietly and listening, no milling about.

After about 15 minutes, I started having a hard time keeping my attention on the speaker, another 15 minutes and I started having desperate thoughts of leaving the room. When I interrupted the speaker and requested that a window or two be opened, the entire room murmured a simultaneous "thank you".

Life without sufficient air is just not pleasant.

-AC

[S-F]

I realized that I simply made a statement about opening a window vs. mechanical ventilation and didn't back it up with any logic. Let's go back to the burnt rice. Imagine your house is filled with smoke because you forgot to turn the burner down on the rice. If you open the window it will take a long time for the smoke to clear out but it will get cold in the room. heat moves in more ways than air does (convection, conduction and radiation). If you put a fan in one window for exhaust and one in an opposing window for intake the air will be clear in a matter of minutes as opposed to hours. Sure the air temp will drop a good deal but it will spring right back up because of the thermal mass of the house and furnishings in addition to the air which is still warm in the adjacent rooms. Opening a window long enough to let the smoke find its way out will drop the temperature for such a long period of time that interior materials will cool down. And the heat source will probably fire up during the time it take for the smoke to clear, wasting more energy.

[Drake]

I've started with superinsulated(R40w/R60c) passive solar two story design that will high thermal mass low temp hydronic radiant heat which can be supplied thru off peak 3.4c/K elect, pump and dump geothermal heat pump or outside wood boiler(have one cost free but not labor free) as it is on 130ac of forestland to provide as cheap as possible backup heat needed over solar gain. It will have a continuous 6ml vapor barrier that is unbroken only by two egress doors and 6 oper windows using inner wall construction that keeps all mech inside it. No combustion inside space, very low VOC construction materials/methods, open room design with forced air filtration as my wife is not bubble person level but chem sensitive. Space has amply solar exposure to incorporate solar air collectors that will provide active space heat and at least tempered fresh air 80% of daylight hours. Previous experience with simple soda can collector heated air over 100F easly. I have designe for maximum solar gain and thermal mass floor storage that also works best for hydronic as I don't have to worry about over heating space because that heat can be exhausted into the unheated half of our cabin to increase livable space when available. I am trying to incorporate low temp wax PC storage into the air collector to extend their ability to heat fresh air and though the ideal materials exist they aren't easily purchase yet. Their are commercial paraffin wax based PCs that change at approx 73 F would work better than just paraffin that require over 100 F air temps. still searching for supplier. Ground tubes are a strong option(especially for night fresh air) as well as I have to dig over 250' of trenches for other things and placing them in the same trench would be minimal cost(as they will only be used to preheat incoming air in winter mold from condensation is improbable and will be set up to be cleanable. If these and other yet to be discovered ideas don't supply enough fresh air for good health than they can at least provide tempered air that would make an HRV not "frost" and make a maybe less than optimal effcnt DIY one a better option. I have not yet come across any research on continuous air exchange vs periodic. I obviously have the advantage of designing/building from scratch for best fresh air.

[S-F]

Is there much radon Radon where you live? There is here and that makes Earth tubes all but useless..... if not actually dangerous. I love the idea but it appears to just not be reasonable in New England. You need to have drains holes in places in the tube and radon will get in there. I'd rather pay more for heat or live a little colder in the winter than have radon in the house. It's just such an enticing and simple idea for something like feeding a HRV. I'm beside myself daily that it won't work for me.

[Drake]

It is unfortunate that a good option for some is not the same for others. I am in a low radon area and my tube runs(two) will be straight downgrade so only a small weep hole will needed. Areas with radon issues will effect the needed fresh air demand if one wants a warm basement space. For me at my age the exposure to all the "bad" things are long done. We played with liquid mercury, asbestos was everywhere and lead was in half the game we ate for dinner if it wasn't fish.

[roxannedetierro]

Being able to breath is essential. Instead of spending lots of cash on electronic devices that filter out airborne pollutants in your home, did you know that certain houseplants contribute a great deal for indoor quality of air? Here are a few relatively affordable ideas for those of you with a green thumb. Mix and match leafy and flowering plants and you'll find yourself breathing more easily very quickly, with a beautiful home to boot.

[Drake]

Any info on whether the demand for fresh air is constant or cyclic thru a day? Less needed during sleep hours, more high activity times? Plants also greatly add to indoor humidity, a plus or minus, depending on how air tight your space.

[AC_Hacker]

Originally Posted by Drake

Any info on whether the demand for fresh air is constant or cyclic thru a day? Less needed during sleep hours, more high activity times? Plants also greatly add to indoor humidity, a plus or minus, depending on how air tight your space.

There is a baseline contamination which is out-gasing from materials and glues and coatings, etc. As I recall, you were planning to go all green materials, so the out-gasing would be less.

Then there's increases in contamination from cooking and cleaning and other activities.

There's also a baseline of metabolic gas (CO2) that needs to be dealt with.

There are also increases in metabolic gas that come from muscular activity.

So yeah, it would vary.

If you do some aggressive Googling, you'll find tables of metabolic rates that might shed light on your question.

I'm working on a CO2 controlled HRV that can sense CO2 levels and increase air replacement as required.

Best,

-AC