8 ms·

> Ducts are dead. Ducts are still needed to circulate air, especially if you want to remove stale air (e.g., bathrooms, kitchen) and bring in (filtered) fresh

> Ducts are dead. Ducts are still needed to circulate air, especially if you want to remove stale air (e.g., bathrooms, kitchen) and bring in (filtered) fresh air (to bedrooms).

kccqzy 4y ago
Not being snarky but why don't you just open the window for that? I have a CO2 detector that I believe is a reasonable proxy for stale air. When it goes above 1000 I simply open the windows. By the time I remember to close the windows the reading is almost always below 500.
- krageon 4y ago
  A ventilation system allows you to filter (not a luxury when you live in a big city, where you will be breathing pollutants otherwise) or perform some thermal magic if the outside air is very cold (or very warm), by running the outflow and inflow pipes really close to each other.
- jwcooper 4y ago
  Where I live, it can get very cold. Not always very efficient to open windows for 5 months out of the year. A great option for keeping CO2 levels down in a house is with an HRV (or ERV) [1] that will heat the fresh air coming in to cycle it throughout the house. [1] https://en.wikipedia.org/wiki/Heat_recovery_ventilation https://en.wikipedia.org/wiki/Heat_recovery_ventilation
  - thadk 4y ago
    There is an open source 3D printable unit design here which I installed in my window and works well for relatively efficiently exhausting the CO2 from one person in cold weather: https://www.openerv.org https://www.openerv.org (license: CC BY-NC-SA 3.0) I did not 3D print mine, but ordered it, though as an early adopter, adjustment was required.
    - pbhjpbhj 4y ago
      Do you know, is there a document explaining the design somewhere? I can see from the Google images some of the parts, but not clearly all the parts nor the flowpaths and such.
  - westurner 4y ago
    From the ERV/HRV (Energy Recovery Ventilation / Heat Recovery Ventilation) wikipedia page: https://en.wikipedia.org/wiki/Energy_recovery_ventilation#Types_of_energy_recovery_devices https://en.wikipedia.org/wiki/Energy_recovery_ventilation#Ty... : > During the warmer seasons, an ERV system pre-cools and dehumidifies; During cooler seasons the system humidifies and pre-heats.[1] An ERV system helps HVAC design meet ventilation and energy standards (e.g., ASHRAE), improves indoor air quality and reduces total HVAC equipment capacity, thereby reducing energy consumption. > ERV systems enable an HVAC system to maintain a 40-50% indoor relative humidity, essentially in all conditions. ERV's must use power for a blower to overcome the pressure drop in the system, hence incurring a slight energy demand. In Jan 2023, the ERV wikipedia article has a 'Table of Energy recovery devices by Types of transfer supported': Total and Sensible : > [ Total & Sensible transfer: Rotary enthalpy wheel, Fixed Plate ] > [ Sensible transfer only: Heat pipe, Run around coil, Thermosiphon, Twin Towers ] Latent heat: https://en.wikipedia.org/wiki/Latent_heat https://en.wikipedia.org/wiki/Latent_heat : > In contrast to latent heat, sensible heat is energy transferred as heat, with a resultant temperature change in a body. Sensible heat: https://en.wikipedia.org/wiki/Sensible_heat https://en.wikipedia.org/wiki/Sensible_heat There's a broader Category:Energy_recovery page which includes heat pumps. https://en.wikipedia.org/wiki/Category:Energy_recovery https://en.wikipedia.org/wiki/Category:Energy_recovery Are heat pumps more efficient than ERVs? Do heat pumps handle relative humidify in the same way as ERVs?:
    - lsaferite 4y ago
      IME you don't use an ERV alone. You'd use it _with_ a Heat Pump. The ERV is all about transferring heat from one airstream to another. It's _not_ a device that manages indoor temperatures though, just recovers some of the latent energy in the air. In the process it's also managing humidity mainly as a by-product. The humidification properties of the ERV allow you to run the Heat Pump in a more efficient manner. I have an HVAC geek friend who explained the whole process, but essentially (in non physics/fluid dynamics[?] terminology), if the Heat Pump doesn't need to dehumidify air it can operate more efficiently.
- WestCoastJustin 4y ago
  On the west coasts of Canada (BC) we've had insane forest fires the past few years and you 100% want to filter the internal air when it's extremely unhealthy outside. We're talking air quality index in the 300+ range or off the charts at times [1]. Plus, we've had these heat domes were it's in the high 30+ and just gross inside, where you really want to open the windows, but you're letting in tons of pollution. Basically, you need to cool off and filter the air at the same time. [1] https://www.airnow.gov/aqi/aqi-basics/ https://www.airnow.gov/aqi/aqi-basics/
  - rofo1 4y ago
    I have a routine for this scenario: open the windows in the morning for 1-2 hours, then close everything and clean the air internally (I have a 24/7 sensor running and know when the air is good or bad). That seemed like the easiest thing to do without making much more complicated system. Basically risk 1hour of bad air for 23h of "clean" air.
  - mrexroad 4y ago
    This. We live <50’ from an expressway, so after air sealing and replacing all of our ducts, I added a MERV 16 filter to our air handler. We had the windows open at night a few years back (no ac as well), and I woke up to smell of smoke from a forest fire after the winds changed direction. AQI2.5 was 200+ inside. Closed windows, ran the fan on high and after a couple minutes the AQI throughout the house was within healthy range (tested multiple locations). Unfortunately our furnace model leaves few realistic options for controlling it programmatically, so I still have to manually turn on the fan when AQI drops.
- nemo44x 4y ago
  Part of it is code. Make-up air systems need a duct for example. Also a lot of people like their air filtered so opening a window isn’t great for that. Also winter.
- mvnuweucxqokii 4y ago
  Not to be snarky, but if the weather outdoors is uncomfortable enough to be using climate control, why would I want to open the window?
  - kccqzy 4y ago
    Because presumably in this case you would want to open a window for fresh air, and simultaneously run your heating system to heat up that fresh air? I was responding to a comment that presupposes the need for fresh air. If you don't need that, feel free to close the windows then.
    - TheSpiceIsLife 4y ago
      Airborne allergens can be an issue, and dust more generally.
      - throwawaylinux 4y ago
        Seems like it would be more efficient to wear a climate controlled bubble suit than heating up entire rooms. And you could even go outside when it is cold or hot or dusty.
    - catiopatio 4y ago
      You do realize that “open the window and hear that air” is massively energy inefficient, right?
      - kccqzy 4y ago
        I don't know; is it more energy inefficient than having a fresh air intake via a duct? Maybe they are comparable in the absence of a heat recovery ventilation system (mentioned by a sibling comment upthread)?
        mvnuweucxqokii 4y ago
        You don't necessarily need to take in fresh air to freshen air in certain ways. It might suffice to pass it though a good filter.
- rubicon33 4y ago
  Which CO2 detector do you have?
  - kccqzy 4y ago
    The one recommended by SwiftOnSecurity years ago. https://twitter.com/swiftonsecurity/status/1223087609221611520 https://twitter.com/swiftonsecurity/status/12230876092216115...
- jahewson 4y ago
  I used to have a bathroom without an extractor and in the winter with the window open the cold air would just cool the walls and cause more condensation there than I’d get with it closed.
  - jansan 4y ago
    On cold days you should open not the windows longer than 5-10 minutes at a time for exactly that reason.
  - iso1631 4y ago
    I have a bathroom without an extractor. If I don't open the window the mirror fogs up in seconds of turning the shower on, and over time I get mould. If I do open the window it stays clear the entire time. By the time I'm out and dry the moist air has left and I close the window. This morning it was -5C, so not cold by continental standards, but certainly cold enough. In the UK recirculating air is very rare. In cases that bathrooms don't have a window (or indeed in new houses where they do) there's an extractor fan, but that just vents the air directly outside.
- adrianmonk 4y ago
  Allergies, humidity, heat, cold, rain, noise, privacy, and the hassle of doing it manually.
- biofunsf 4y ago
  digression: Any recommendations for a good CO2 detector?
  - imp0cat 4y ago
    TFA Dostmann AirCO2ntrol Mini is a relatively cheap one that works well.
  - NavinF 4y ago
    AutoPilot APCEM2 The only requirement is "2 channel low drift NDIR gas sensor". Cheap CO2 detectors either have zero IR sensors (instead they guesstimate eCO2 using a VOC sensor) or a single IR sensor that requires weekly calibration outdoors or it will just assume that the lowest sensor reading means 400ppm.
newmac 4y ago
Agree, ducts are wonderful! If you don't have ducts, go ductless for sure.
- code_biologist 4y ago
  Am I crazy, or are those two sentences completely contradictory?
  - krageon 4y ago
    I thought it was a joke. If you don't have ducts, you are by definition ductless. So that's how you must go.
    - Dylan16807 4y ago
      > So that's how you must go. No, you can go to ducts by installing them. I believe the comment is advising against doing so.
  - aclatuts 4y ago
    I think he means having a duct work for the whole house for a central heat pump is good. But having a heat pump per zone is also good if you don't have ducts for the whole house. Some newer home designs separate heating and cooling from the air exchange systems so there are multiple zones of heating and cooling.
  - aftbit 4y ago
    I read it as: Ducts are better but not so much that it's worth tearing everything apart to install them. If you don't already have ducts, you should definitely use a ductless system. If you do have them, you get some other benefits.
    - notyourwork 4y ago
      Ducts are great with a heat pump and an air handler with variable fan speed.
dublinben 4y ago
They're obviously no replacement for exhaust fans in bathrooms and kitchens, but there's a number of ductless energy recovery ventilators that can give you fresh air in your bedroom(s). https://www.buildwithrise.com/stories/ductless-heat-recovery https://www.buildwithrise.com/stories/ductless-heat-recovery
- 2sk21 4y ago
  Thank you - this could solve a problem in my house. We had CO2 build up in our bedrooms and the only way I have found to ameliorate the problem is to have our HVAC fan running continuously at night to circulate the air in our house.
fifteenforty 4y ago
A recirculating central heating system doesn't do that. As mentioned below you either need exhaust only ventilation, balanced ventilation or ideally ERV/HRV. All of the above are available in both ducted and ductless forms.
- operatingthetan 4y ago
  Good callout. Some people have the strangest reasons to hate high-efficiency ductless systems.
  - throwawayacc3 4y ago
    Except it's incorrect. The best system is a "ducted ductless" system that circulates and filters air throughout the house.
    - fifteenforty 4y ago
      I've seen that terminology used on US websites, it took me a while to get my head around. In Australia it would just be called ducted reverse cycle. In the vast majority of cases it would be "ducted ductless" I guess: outside unit connects via refrigerant lines to a heat exchanger and fan in the roof cavity, when then distributes the heated/cooled air to rooms via conventional ducting.
      - operatingthetan 4y ago
        Nobody calls it that (ducted ductless), it would just be called a ducted heat pump. The refrigerant lines just run to a central air handler where the ducts start in the house, instead of the air handlers that mount on the walls.
    - deleted 4y ago
      [deleted]
  - nsxwolf 4y ago
    How do you go ductless in a 6000 sq ft home?
jethro_tell 4y ago
In have ducted mini split units in my home, made by Mitsubishi I designed the system to work with merv 13-16 filters. I can run the fans and filter my air as well as use the units for heat and cooling. I installed fresh air intakes on the return units that can pull external air when they are opened. It's really a very good proposition. Has all of the advantages of central heating and the efficiencies the heat pumps

> Ducts are dead. Ducts are still needed to circulate air, especially if you want to remove stale air (e.g., bathrooms, kitchen) and bring in (filtered) fresh air (to bedrooms).

kccqzy 4y ago

Not being snarky but why don't you just open the window for that? I have a CO2 detector that I believe is a reasonable proxy for stale air. When it goes above 1000 I simply open the windows. By the time I remember to close the windows the reading is almost always below 500.

krageon 4y ago
A ventilation system allows you to filter (not a luxury when you live in a big city, where you will be breathing pollutants otherwise) or perform some thermal magic if the outside air is very cold (or very warm), by running the outflow and inflow pipes really close to each other.
jwcooper 4y ago
Where I live, it can get very cold. Not always very efficient to open windows for 5 months out of the year. A great option for keeping CO2 levels down in a house is with an HRV (or ERV) [1] that will heat the fresh air coming in to cycle it throughout the house. [1] https://en.wikipedia.org/wiki/Heat_recovery_ventilation https://en.wikipedia.org/wiki/Heat_recovery_ventilation
- thadk 4y ago
  There is an open source 3D printable unit design here which I installed in my window and works well for relatively efficiently exhausting the CO2 from one person in cold weather: https://www.openerv.org https://www.openerv.org (license: CC BY-NC-SA 3.0) I did not 3D print mine, but ordered it, though as an early adopter, adjustment was required.
  - pbhjpbhj 4y ago
    Do you know, is there a document explaining the design somewhere? I can see from the Google images some of the parts, but not clearly all the parts nor the flowpaths and such.
- westurner 4y ago
  From the ERV/HRV (Energy Recovery Ventilation / Heat Recovery Ventilation) wikipedia page: https://en.wikipedia.org/wiki/Energy_recovery_ventilation#Types_of_energy_recovery_devices https://en.wikipedia.org/wiki/Energy_recovery_ventilation#Ty... : > During the warmer seasons, an ERV system pre-cools and dehumidifies; During cooler seasons the system humidifies and pre-heats.[1] An ERV system helps HVAC design meet ventilation and energy standards (e.g., ASHRAE), improves indoor air quality and reduces total HVAC equipment capacity, thereby reducing energy consumption. > ERV systems enable an HVAC system to maintain a 40-50% indoor relative humidity, essentially in all conditions. ERV's must use power for a blower to overcome the pressure drop in the system, hence incurring a slight energy demand. In Jan 2023, the ERV wikipedia article has a 'Table of Energy recovery devices by Types of transfer supported': Total and Sensible : > [ Total & Sensible transfer: Rotary enthalpy wheel, Fixed Plate ] > [ Sensible transfer only: Heat pipe, Run around coil, Thermosiphon, Twin Towers ] Latent heat: https://en.wikipedia.org/wiki/Latent_heat https://en.wikipedia.org/wiki/Latent_heat : > In contrast to latent heat, sensible heat is energy transferred as heat, with a resultant temperature change in a body. Sensible heat: https://en.wikipedia.org/wiki/Sensible_heat https://en.wikipedia.org/wiki/Sensible_heat There's a broader Category:Energy_recovery page which includes heat pumps. https://en.wikipedia.org/wiki/Category:Energy_recovery https://en.wikipedia.org/wiki/Category:Energy_recovery Are heat pumps more efficient than ERVs? Do heat pumps handle relative humidify in the same way as ERVs?:
  - lsaferite 4y ago
    IME you don't use an ERV alone. You'd use it _with_ a Heat Pump. The ERV is all about transferring heat from one airstream to another. It's _not_ a device that manages indoor temperatures though, just recovers some of the latent energy in the air. In the process it's also managing humidity mainly as a by-product. The humidification properties of the ERV allow you to run the Heat Pump in a more efficient manner. I have an HVAC geek friend who explained the whole process, but essentially (in non physics/fluid dynamics[?] terminology), if the Heat Pump doesn't need to dehumidify air it can operate more efficiently.
WestCoastJustin 4y ago
On the west coasts of Canada (BC) we've had insane forest fires the past few years and you 100% want to filter the internal air when it's extremely unhealthy outside. We're talking air quality index in the 300+ range or off the charts at times [1]. Plus, we've had these heat domes were it's in the high 30+ and just gross inside, where you really want to open the windows, but you're letting in tons of pollution. Basically, you need to cool off and filter the air at the same time. [1] https://www.airnow.gov/aqi/aqi-basics/ https://www.airnow.gov/aqi/aqi-basics/
- rofo1 4y ago
  I have a routine for this scenario: open the windows in the morning for 1-2 hours, then close everything and clean the air internally (I have a 24/7 sensor running and know when the air is good or bad). That seemed like the easiest thing to do without making much more complicated system. Basically risk 1hour of bad air for 23h of "clean" air.
- mrexroad 4y ago
  This. We live <50’ from an expressway, so after air sealing and replacing all of our ducts, I added a MERV 16 filter to our air handler. We had the windows open at night a few years back (no ac as well), and I woke up to smell of smoke from a forest fire after the winds changed direction. AQI2.5 was 200+ inside. Closed windows, ran the fan on high and after a couple minutes the AQI throughout the house was within healthy range (tested multiple locations). Unfortunately our furnace model leaves few realistic options for controlling it programmatically, so I still have to manually turn on the fan when AQI drops.
nemo44x 4y ago
Part of it is code. Make-up air systems need a duct for example. Also a lot of people like their air filtered so opening a window isn’t great for that. Also winter.
mvnuweucxqokii 4y ago
Not to be snarky, but if the weather outdoors is uncomfortable enough to be using climate control, why would I want to open the window?
- kccqzy 4y ago
  Because presumably in this case you would want to open a window for fresh air, and simultaneously run your heating system to heat up that fresh air? I was responding to a comment that presupposes the need for fresh air. If you don't need that, feel free to close the windows then.
  - TheSpiceIsLife 4y ago
    Airborne allergens can be an issue, and dust more generally.
    - throwawaylinux 4y ago
      Seems like it would be more efficient to wear a climate controlled bubble suit than heating up entire rooms. And you could even go outside when it is cold or hot or dusty.
  - catiopatio 4y ago
    You do realize that “open the window and hear that air” is massively energy inefficient, right?
    - kccqzy 4y ago
      I don't know; is it more energy inefficient than having a fresh air intake via a duct? Maybe they are comparable in the absence of a heat recovery ventilation system (mentioned by a sibling comment upthread)?
      - mvnuweucxqokii 4y ago
        You don't necessarily need to take in fresh air to freshen air in certain ways. It might suffice to pass it though a good filter.
rubicon33 4y ago
Which CO2 detector do you have?
- kccqzy 4y ago
  The one recommended by SwiftOnSecurity years ago. https://twitter.com/swiftonsecurity/status/1223087609221611520 https://twitter.com/swiftonsecurity/status/12230876092216115...
jahewson 4y ago
I used to have a bathroom without an extractor and in the winter with the window open the cold air would just cool the walls and cause more condensation there than I’d get with it closed.
- jansan 4y ago
  On cold days you should open not the windows longer than 5-10 minutes at a time for exactly that reason.
- iso1631 4y ago
  I have a bathroom without an extractor. If I don't open the window the mirror fogs up in seconds of turning the shower on, and over time I get mould. If I do open the window it stays clear the entire time. By the time I'm out and dry the moist air has left and I close the window. This morning it was -5C, so not cold by continental standards, but certainly cold enough. In the UK recirculating air is very rare. In cases that bathrooms don't have a window (or indeed in new houses where they do) there's an extractor fan, but that just vents the air directly outside.
adrianmonk 4y ago
Allergies, humidity, heat, cold, rain, noise, privacy, and the hassle of doing it manually.
biofunsf 4y ago
digression: Any recommendations for a good CO2 detector?
- imp0cat 4y ago
  TFA Dostmann AirCO2ntrol Mini is a relatively cheap one that works well.
- NavinF 4y ago
  AutoPilot APCEM2 The only requirement is "2 channel low drift NDIR gas sensor". Cheap CO2 detectors either have zero IR sensors (instead they guesstimate eCO2 using a VOC sensor) or a single IR sensor that requires weekly calibration outdoors or it will just assume that the lowest sensor reading means 400ppm.

newmac 4y ago

Agree, ducts are wonderful! If you don't have ducts, go ductless for sure.

code_biologist 4y ago
Am I crazy, or are those two sentences completely contradictory?
- krageon 4y ago
  I thought it was a joke. If you don't have ducts, you are by definition ductless. So that's how you must go.
  - Dylan16807 4y ago
    > So that's how you must go. No, you can go to ducts by installing them. I believe the comment is advising against doing so.
- aclatuts 4y ago
  I think he means having a duct work for the whole house for a central heat pump is good. But having a heat pump per zone is also good if you don't have ducts for the whole house. Some newer home designs separate heating and cooling from the air exchange systems so there are multiple zones of heating and cooling.
- aftbit 4y ago
  I read it as: Ducts are better but not so much that it's worth tearing everything apart to install them. If you don't already have ducts, you should definitely use a ductless system. If you do have them, you get some other benefits.
  - notyourwork 4y ago
    Ducts are great with a heat pump and an air handler with variable fan speed.

dublinben 4y ago

They're obviously no replacement for exhaust fans in bathrooms and kitchens, but there's a number of ductless energy recovery ventilators that can give you fresh air in your bedroom(s). https://www.buildwithrise.com/stories/ductless-heat-recovery https://www.buildwithrise.com/stories/ductless-heat-recovery

2sk21 4y ago
Thank you - this could solve a problem in my house. We had CO2 build up in our bedrooms and the only way I have found to ameliorate the problem is to have our HVAC fan running continuously at night to circulate the air in our house.

fifteenforty 4y ago

A recirculating central heating system doesn't do that. As mentioned below you either need exhaust only ventilation, balanced ventilation or ideally ERV/HRV. All of the above are available in both ducted and ductless forms.

operatingthetan 4y ago
Good callout. Some people have the strangest reasons to hate high-efficiency ductless systems.
- throwawayacc3 4y ago
  Except it's incorrect. The best system is a "ducted ductless" system that circulates and filters air throughout the house.
  - fifteenforty 4y ago
    I've seen that terminology used on US websites, it took me a while to get my head around. In Australia it would just be called ducted reverse cycle. In the vast majority of cases it would be "ducted ductless" I guess: outside unit connects via refrigerant lines to a heat exchanger and fan in the roof cavity, when then distributes the heated/cooled air to rooms via conventional ducting.
    - operatingthetan 4y ago
      Nobody calls it that (ducted ductless), it would just be called a ducted heat pump. The refrigerant lines just run to a central air handler where the ducts start in the house, instead of the air handlers that mount on the walls.
  - deleted 4y ago
    [deleted]
- nsxwolf 4y ago
  How do you go ductless in a 6000 sq ft home?

jethro_tell 4y ago

In have ducted mini split units in my home, made by Mitsubishi I designed the system to work with merv 13-16 filters. I can run the fans and filter my air as well as use the units for heat and cooling. I installed fresh air intakes on the return units that can pull external air when they are opened. It's really a very good proposition. Has all of the advantages of central heating and the efficiencies the heat pumps