6 ms·

As someone who has built my fair share of houses and worked on many more over the last 25 years, I have to agree that our ability to seal air better than ever i

As someone who has built my fair share of houses and worked on many more over the last 25 years, I have to agree that our ability to seal air better than ever is causing problems, especially if you don't have forced air heating and cooling running all the time. People just completely ignore or haven't ever thought about room ventilation, positive or negative room pressures, and where and how to ventilate to the outside. In older houses there was always air leaks, small, but they let the house breath, especially if you had a central fireplace and your house was at negative pressure. I have seen many people purposefully over seal their house in ill conceived ways, to try and improve insulation, but end up causing ventilation problems with mold being especially common. Materials and vents that should let air pass through are commonly replaced with impermeable plastics and sealing tapes, many times in conjunction with a misunderstanding in expansion and contraction joints that have small gaps.

marricks 8y ago
And I recently remember hearing forced air is bad for air quality inside! Did I hear wrong or is there something more to the story like “forced air brings in outside air, so if your outside air is bad you’ll have trouble”?
- Kadin 8y ago
  Most residential forced-air systems don't bring in air from outside (intentionally at least). They recirculate the air in the building through the heating/cooling unit (typically a combination updraft furnace with AC evaporator sitting on top). Modern systems (since late 80s, maybe?) have return air ducts so that you get even heating even if interior doors (e.g. bedroom doors) are closed, but older systems may only have one return vent per floor or even just a single one in the house, and depend on gaps under doors and such for return air circulation. Bigger commercial forced-air systems have had exterior air intakes and heat exchanger systems for a while, but are pretty new for residential (I've never seen one in the wild myself).
  - gregmac 8y ago
    Heat recovery ventilators [1] are reasonably common in Canada. Most (all?) EnergyStar homes [2] have one, and they includes most if not all the houses I've looked at (or friends have bought) in the past decade or so. I lived in a house built around 1985 that had one, which was R-2000 [3], so they're at least that old. [1] https://en.m.wikipedia.org/wiki/Heat_recovery_ventilation https://en.m.wikipedia.org/wiki/Heat_recovery_ventilation [2] https://www.nrcan.gc.ca/energy/efficiency/housing/new-homes/5057 https://www.nrcan.gc.ca/energy/efficiency/housing/new-homes/... [3] https://www.nrcan.gc.ca/energy/efficiency/homes/20575 https://www.nrcan.gc.ca/energy/efficiency/homes/20575
    - gregmac 8y ago
      Oops, I meant houses that were built in the last ~decade are mostly EnergyStar.
- millettjon 8y ago
  You can add filters on the blower to clean up the air. Especially important in cities.
  - twothamendment 8y ago
    Also important in the middle of nowhere when the clean, forest air turns to smoke each August.
segmondy 8y ago
I have a 100+yr old house, no vents. Old style radiator. Doors have large gaps underneath them, the holes on the floor that the radiator pipes travel through have gaps that you can feel the draft. It's annoying, but the house really does breath and is noticeable comfortable for me unlike houses with forced heat that are sealed well.
- throw0101a 8y ago
  That draft you feel is money going out the (proverbial) window. It's better to stop the air going in/out through walls, doors, and windows, and bring it in in a controlled fashion: * https://www.youtube.com/watch?v=CIcrXut_EFA https://www.youtube.com/watch?v=CIcrXut_EFA The problem is that many retrofits don't bring in outside air into the mix and just recirculate what's already in the house. This is not current best practice.
  - AstralStorm 8y ago
    Any kind of air exchange will cause heat loss or gain, decreasing insulation. Does not matter if it's through wall or HVAC. If there is no draft, it means there is no air circulation. The only difference is if the draft goes through HVAC vents or through unsealed doors and windows, or through walls. If your local heaters are effective and seal controllable, there should be really no difference in many municipal settings as the heating is waste heat from electricity generation anyway. (Those cooling towers "greens" love to hate.) Certain baseline air flow is strictly required and it is quite a lot, especially in small volumes. Now, if you have to burn something to heat, then by all means do install a heatpipe recovery system.
    - throw0101a 8y ago
      You're not wrong, but one can mitigate energy loss with an HRV (or ERV) and get fresh air in a controlled manner: * https://en.wikipedia.org/wiki/Heat_recovery_ventilation https://en.wikipedia.org/wiki/Heat_recovery_ventilation With the added bonus that the air can be filtered as well, instead of coming in as-in through leakage.
tylerl 8y ago
Apparently certain residential building codes have air-freshness provisions: I recently added A/C cooling to a previously heat-only house, and I took the opportunity to ask the company to explain some quirks in the existing system, like how the ventilation fan in the laundry room is on the same breaker as the central heating, and had a hidden timer attached to it. The house was built (early 1990s) with a particularly powerful vent fan in the laundry room which was on (regardless of the wall switch) a certain number of hours a day, and the forced-air system had an air intake outside the house which mixed with the return air before hitting the filter. This was all sized such that all the air in the house would be replaced about once every 24 hours, according to WA state's VIAQ ("Ventilation and Indoor Air Quality") code. That's all been superseded by the International Mechanical Code and International Residential Code.
- throw0101a 8y ago
  See also ANSI/ASHRAE Standard 62.1-2016: * https://www.ashrae.org/technical-resources/bookstore/standards-62-1-62-2 https://www.ashrae.org/technical-resources/bookstore/standar...
sam_goody 8y ago
What's the solution? My house is absolutely frigid during the winter, and I got quote for resealing it. He told me that afterwards I am either going to have to leave my windows open (no thanks!) or live with mold. I've heard that you can install vents, but can't find useful info. My grandparents had a chute vent, and it somehow became a breeding ground for flies and all sorts of ichies. Not sure why. And short vents sound to me like an always open wondow, which just brings in the cold. I want the insulation, the circulation, the breathability and the warmth. Is there any way to have it all?
- extrapickles 8y ago
  Heat recovery ventilation can bring in fresh air with about half the heat loss, but it needs regular maintenance. You can also look at whole house dehumidifiers to take the water out of the air to help reduce the mold problem.
- throw0101a 8y ago
  Yes. Matt Risinger has a really good channel on building science, and this video is a pretty good intro on air tight houses and ventilation: * https://www.youtube.com/watch?v=CIcrXut_EFA https://www.youtube.com/watch?v=CIcrXut_EFA Go through the archives as well. Lot's of good stuff. He's based in Austin, TX, so needs to worry about heat and humidity being kept out, but the principles also apply for colder climate where the cold needs to stay on the outside. Another good person is Lstiburek, and his concept of the "perfect wall": * https://buildingscience.com/documents/insights/bsi-001-the-perfect-wall https://buildingscience.com/documents/insights/bsi-001-the-p...
dangravell 8y ago
> As someone who has built my fair share of houses and worked on many more over the last 25 years, I have to agree that our ability to seal air better than ever is causing problems, especially if you don't have forced air heating and cooling running all the time. People just completely ignore or haven't ever thought about room ventilation, positive or negative room pressures, and where and how to ventilate to the outside. In older houses there was always air leaks, small, but they let the house breath, especially if you had a central fireplace and your house was at negative pressure. I have seen many people purposefully over seal their house in ill conceived ways, to try and improve insulation, but end up causing ventilation problems with mold being especially common. Materials and vents that should let air pass through are commonly replaced with impermeable plastics and sealing tapes, many times in conjunction with a misunderstanding in expansion and contraction joints that have small gaps. Sorry, but this is just wrong and is the type of "accepted wisdom" that holds back construction, particularly here in the UK. Repeat: ventilation and permeability are different things. Yes, permeability can achieve some ventilation but it comes at the cost of: 1) Not being reliable; it is dependent on pressure deltas around the dwelling. 2) Being potentially deleterious to the fabric of the building where escaping warm air cools and water condenses on surfaces in the fabric. 3) Being wasteful of energy. The solution is to separate the two: 1) Seal the fabric totally, bearing in mind vapour permeability. The seal should be on the warm side of the insulation. 2) Install a ventilation system which provides reliable fresh air and, ideally, exchanges the heat leaving the building with the fresh air coming in. We can no longer rely on folksy wisdom. Let's engineer our houses.
- throw0101a 8y ago
  You may be interested in the "perfect wall" concept by Joseph Lstiburek: * https://buildingscience.com/documents/insights/bsi-001-the-perfect-wall https://buildingscience.com/documents/insights/bsi-001-the-p... Also check out Matt Risinger. They both have various good content on building science.
  - dangravell 8y ago
    Thanks for the reference. Trouble is there is no one "perfect" - depends on so many other constraints.
mikorym 8y ago
This is a bit of a side quest comment. South Africans are (at least historically) quite different in this respect. Everyone is cold in the winter due to complete disregard for insulation (at least, when compared to Europe). People also don't get layering. The comments about construction do hold mostly. In the warmer areas of the country usually you are cold in the winters for only a couple hours per day. When we go overseas we tend to open all the windows. Maybe this is because we are not used to long winters. My grandparents were experts at opening select windows in their houses to create drafts in the pre-aircon age. There is a meme: "If a guy invites you to a braai at his home at 3am, it really is a braai."
throw0101a 8y ago
A house should not breathe. A catchy mantra I've run across is "seal tight, ventilate right": * https://www.youtube.com/watch?v=CIcrXut_EFA https://www.youtube.com/watch?v=CIcrXut_EFA Mold is not a ventilation problem, but rather a moisture control problem. Keep the humidity down (especially with whole house dehumidifiers), and eliminate condensation points (by eliminating thermal bridging), and it goes away. While the above video, which is from the really good channel by Matt Risinger, is a good introduction, I recommend you also check out the building science stuff put out by Joseph Lstiburek for a more science-y explanation: * https://en.wikipedia.org/wiki/Joseph_Lstiburek https://en.wikipedia.org/wiki/Joseph_Lstiburek On the "perfect wall": * https://buildingscience.com/documents/insights/bsi-001-the-perfect-wall https://buildingscience.com/documents/insights/bsi-001-the-p... Presentation on control layer (especially starting around 15m): * https://www.youtube.com/watch?v=rkfAcWpOYAA https://www.youtube.com/watch?v=rkfAcWpOYAA Good webinar: * https://www.youtube.com/watch?v=sBcNFeiWjrg https://www.youtube.com/watch?v=sBcNFeiWjrg
- chrismeller 8y ago
  > Mold is not a ventilation problem, but rather a moisture control problem. Keep the humidity down (especially with whole house dehumidifiers), and eliminate condensation points (by eliminating thermal bridging), and it goes away. This sounds like one of those kinds of answers that only works with spherical cows in a vacuum. If my shower were completely open and in the middle of the living room, perhaps. Alas, it's in a small private room that usually has the door closed while in use, and now we've circled back around to ventilation...
  - throw0101a 8y ago
    Yup, ventilate right: * https://www.youtube.com/watch?v=Ulaz3aUSZlQ https://www.youtube.com/watch?v=Ulaz3aUSZlQ * https://www.youtube.com/watch?v=-3CRGhu8C5I https://www.youtube.com/watch?v=-3CRGhu8C5I There are houses that are almost hermetically sealed, and do not have issues because they control temperature and humidity properly: * https://en.wikipedia.org/wiki/Passive_house#Airtightness https://en.wikipedia.org/wiki/Passive_house#Airtightness
- 8y ago

marricks 8y ago

And I recently remember hearing forced air is bad for air quality inside! Did I hear wrong or is there something more to the story like “forced air brings in outside air, so if your outside air is bad you’ll have trouble”?

Kadin 8y ago
Most residential forced-air systems don't bring in air from outside (intentionally at least). They recirculate the air in the building through the heating/cooling unit (typically a combination updraft furnace with AC evaporator sitting on top). Modern systems (since late 80s, maybe?) have return air ducts so that you get even heating even if interior doors (e.g. bedroom doors) are closed, but older systems may only have one return vent per floor or even just a single one in the house, and depend on gaps under doors and such for return air circulation. Bigger commercial forced-air systems have had exterior air intakes and heat exchanger systems for a while, but are pretty new for residential (I've never seen one in the wild myself).
- gregmac 8y ago
  Heat recovery ventilators [1] are reasonably common in Canada. Most (all?) EnergyStar homes [2] have one, and they includes most if not all the houses I've looked at (or friends have bought) in the past decade or so. I lived in a house built around 1985 that had one, which was R-2000 [3], so they're at least that old. [1] https://en.m.wikipedia.org/wiki/Heat_recovery_ventilation https://en.m.wikipedia.org/wiki/Heat_recovery_ventilation [2] https://www.nrcan.gc.ca/energy/efficiency/housing/new-homes/5057 https://www.nrcan.gc.ca/energy/efficiency/housing/new-homes/... [3] https://www.nrcan.gc.ca/energy/efficiency/homes/20575 https://www.nrcan.gc.ca/energy/efficiency/homes/20575
  - gregmac 8y ago
    Oops, I meant houses that were built in the last ~decade are mostly EnergyStar.
millettjon 8y ago
You can add filters on the blower to clean up the air. Especially important in cities.
- twothamendment 8y ago
  Also important in the middle of nowhere when the clean, forest air turns to smoke each August.

segmondy 8y ago

I have a 100+yr old house, no vents. Old style radiator. Doors have large gaps underneath them, the holes on the floor that the radiator pipes travel through have gaps that you can feel the draft. It's annoying, but the house really does breath and is noticeable comfortable for me unlike houses with forced heat that are sealed well.

throw0101a 8y ago
That draft you feel is money going out the (proverbial) window. It's better to stop the air going in/out through walls, doors, and windows, and bring it in in a controlled fashion: * https://www.youtube.com/watch?v=CIcrXut_EFA https://www.youtube.com/watch?v=CIcrXut_EFA The problem is that many retrofits don't bring in outside air into the mix and just recirculate what's already in the house. This is not current best practice.
- AstralStorm 8y ago
  Any kind of air exchange will cause heat loss or gain, decreasing insulation. Does not matter if it's through wall or HVAC. If there is no draft, it means there is no air circulation. The only difference is if the draft goes through HVAC vents or through unsealed doors and windows, or through walls. If your local heaters are effective and seal controllable, there should be really no difference in many municipal settings as the heating is waste heat from electricity generation anyway. (Those cooling towers "greens" love to hate.) Certain baseline air flow is strictly required and it is quite a lot, especially in small volumes. Now, if you have to burn something to heat, then by all means do install a heatpipe recovery system.
  - throw0101a 8y ago
    You're not wrong, but one can mitigate energy loss with an HRV (or ERV) and get fresh air in a controlled manner: * https://en.wikipedia.org/wiki/Heat_recovery_ventilation https://en.wikipedia.org/wiki/Heat_recovery_ventilation With the added bonus that the air can be filtered as well, instead of coming in as-in through leakage.

tylerl 8y ago

Apparently certain residential building codes have air-freshness provisions: I recently added A/C cooling to a previously heat-only house, and I took the opportunity to ask the company to explain some quirks in the existing system, like how the ventilation fan in the laundry room is on the same breaker as the central heating, and had a hidden timer attached to it. The house was built (early 1990s) with a particularly powerful vent fan in the laundry room which was on (regardless of the wall switch) a certain number of hours a day, and the forced-air system had an air intake outside the house which mixed with the return air before hitting the filter. This was all sized such that all the air in the house would be replaced about once every 24 hours, according to WA state's VIAQ ("Ventilation and Indoor Air Quality") code. That's all been superseded by the International Mechanical Code and International Residential Code.

throw0101a 8y ago
See also ANSI/ASHRAE Standard 62.1-2016: * https://www.ashrae.org/technical-resources/bookstore/standards-62-1-62-2 https://www.ashrae.org/technical-resources/bookstore/standar...

sam_goody 8y ago

What's the solution? My house is absolutely frigid during the winter, and I got quote for resealing it. He told me that afterwards I am either going to have to leave my windows open (no thanks!) or live with mold. I've heard that you can install vents, but can't find useful info. My grandparents had a chute vent, and it somehow became a breeding ground for flies and all sorts of ichies. Not sure why. And short vents sound to me like an always open wondow, which just brings in the cold. I want the insulation, the circulation, the breathability and the warmth. Is there any way to have it all?

extrapickles 8y ago
Heat recovery ventilation can bring in fresh air with about half the heat loss, but it needs regular maintenance. You can also look at whole house dehumidifiers to take the water out of the air to help reduce the mold problem.
throw0101a 8y ago
Yes. Matt Risinger has a really good channel on building science, and this video is a pretty good intro on air tight houses and ventilation: * https://www.youtube.com/watch?v=CIcrXut_EFA https://www.youtube.com/watch?v=CIcrXut_EFA Go through the archives as well. Lot's of good stuff. He's based in Austin, TX, so needs to worry about heat and humidity being kept out, but the principles also apply for colder climate where the cold needs to stay on the outside. Another good person is Lstiburek, and his concept of the "perfect wall": * https://buildingscience.com/documents/insights/bsi-001-the-perfect-wall https://buildingscience.com/documents/insights/bsi-001-the-p...

dangravell 8y ago

> As someone who has built my fair share of houses and worked on many more over the last 25 years, I have to agree that our ability to seal air better than ever is causing problems, especially if you don't have forced air heating and cooling running all the time. People just completely ignore or haven't ever thought about room ventilation, positive or negative room pressures, and where and how to ventilate to the outside. In older houses there was always air leaks, small, but they let the house breath, especially if you had a central fireplace and your house was at negative pressure. I have seen many people purposefully over seal their house in ill conceived ways, to try and improve insulation, but end up causing ventilation problems with mold being especially common. Materials and vents that should let air pass through are commonly replaced with impermeable plastics and sealing tapes, many times in conjunction with a misunderstanding in expansion and contraction joints that have small gaps. Sorry, but this is just wrong and is the type of "accepted wisdom" that holds back construction, particularly here in the UK. Repeat: ventilation and permeability are different things. Yes, permeability can achieve some ventilation but it comes at the cost of: 1) Not being reliable; it is dependent on pressure deltas around the dwelling. 2) Being potentially deleterious to the fabric of the building where escaping warm air cools and water condenses on surfaces in the fabric. 3) Being wasteful of energy. The solution is to separate the two: 1) Seal the fabric totally, bearing in mind vapour permeability. The seal should be on the warm side of the insulation. 2) Install a ventilation system which provides reliable fresh air and, ideally, exchanges the heat leaving the building with the fresh air coming in. We can no longer rely on folksy wisdom. Let's engineer our houses.

throw0101a 8y ago
You may be interested in the "perfect wall" concept by Joseph Lstiburek: * https://buildingscience.com/documents/insights/bsi-001-the-perfect-wall https://buildingscience.com/documents/insights/bsi-001-the-p... Also check out Matt Risinger. They both have various good content on building science.
- dangravell 8y ago
  Thanks for the reference. Trouble is there is no one "perfect" - depends on so many other constraints.

mikorym 8y ago

This is a bit of a side quest comment. South Africans are (at least historically) quite different in this respect. Everyone is cold in the winter due to complete disregard for insulation (at least, when compared to Europe). People also don't get layering. The comments about construction do hold mostly. In the warmer areas of the country usually you are cold in the winters for only a couple hours per day. When we go overseas we tend to open all the windows. Maybe this is because we are not used to long winters. My grandparents were experts at opening select windows in their houses to create drafts in the pre-aircon age. There is a meme: "If a guy invites you to a braai at his home at 3am, it really is a braai."

throw0101a 8y ago

A house should not breathe. A catchy mantra I've run across is "seal tight, ventilate right": * https://www.youtube.com/watch?v=CIcrXut_EFA https://www.youtube.com/watch?v=CIcrXut_EFA Mold is not a ventilation problem, but rather a moisture control problem. Keep the humidity down (especially with whole house dehumidifiers), and eliminate condensation points (by eliminating thermal bridging), and it goes away. While the above video, which is from the really good channel by Matt Risinger, is a good introduction, I recommend you also check out the building science stuff put out by Joseph Lstiburek for a more science-y explanation: * https://en.wikipedia.org/wiki/Joseph_Lstiburek https://en.wikipedia.org/wiki/Joseph_Lstiburek On the "perfect wall": * https://buildingscience.com/documents/insights/bsi-001-the-perfect-wall https://buildingscience.com/documents/insights/bsi-001-the-p... Presentation on control layer (especially starting around 15m): * https://www.youtube.com/watch?v=rkfAcWpOYAA https://www.youtube.com/watch?v=rkfAcWpOYAA Good webinar: * https://www.youtube.com/watch?v=sBcNFeiWjrg https://www.youtube.com/watch?v=sBcNFeiWjrg

chrismeller 8y ago
> Mold is not a ventilation problem, but rather a moisture control problem. Keep the humidity down (especially with whole house dehumidifiers), and eliminate condensation points (by eliminating thermal bridging), and it goes away. This sounds like one of those kinds of answers that only works with spherical cows in a vacuum. If my shower were completely open and in the middle of the living room, perhaps. Alas, it's in a small private room that usually has the door closed while in use, and now we've circled back around to ventilation...
- throw0101a 8y ago
  Yup, ventilate right: * https://www.youtube.com/watch?v=Ulaz3aUSZlQ https://www.youtube.com/watch?v=Ulaz3aUSZlQ * https://www.youtube.com/watch?v=-3CRGhu8C5I https://www.youtube.com/watch?v=-3CRGhu8C5I There are houses that are almost hermetically sealed, and do not have issues because they control temperature and humidity properly: * https://en.wikipedia.org/wiki/Passive_house#Airtightness https://en.wikipedia.org/wiki/Passive_house#Airtightness
8y ago