ᐅ Controlled residential ventilation in the basement with outdoor air supplied through the roof
Created on: 6 Apr 2021 20:40
U
uncelsam
Hello everyone,
We are currently in the final planning stages of our house with a basement granny flat (KFW40+).
We definitely want a controlled mechanical ventilation system, but we would prefer to avoid an outdoor air intake pipe in the garden. So, the idea came up to draw the outdoor air from the roof (the attic is outside the thermal envelope and insulated with only 60mm (2.4 inches) of wood fiber board).
The exhaust air would then be vented through a light well.
Is there any reason this might not work, apart from the fact that my outdoor air intake path would be significantly longer than the exhaust air path?
Thanks and best regards
We are currently in the final planning stages of our house with a basement granny flat (KFW40+).
We definitely want a controlled mechanical ventilation system, but we would prefer to avoid an outdoor air intake pipe in the garden. So, the idea came up to draw the outdoor air from the roof (the attic is outside the thermal envelope and insulated with only 60mm (2.4 inches) of wood fiber board).
The exhaust air would then be vented through a light well.
Is there any reason this might not work, apart from the fact that my outdoor air intake path would be significantly longer than the exhaust air path?
Thanks and best regards
Hello,
I would suggest drawing outdoor air through an intake shaft and then a ground heat exchanger. This way, you avoid problems with air that is too cold in winter, and in summer the air is pre-cooled to about 20-22°C (68-72°F). This doesn’t provide real cooling in summer, but at least you won’t be bringing additional heat inside the house.
If you’re willing to do a bit of DIY, I would recommend using a storage box (search for Biohort and “Auflagenbox”) instead of an intake shaft to draw the air through.
Why?
Best regards,
Andreas
I would suggest drawing outdoor air through an intake shaft and then a ground heat exchanger. This way, you avoid problems with air that is too cold in winter, and in summer the air is pre-cooled to about 20-22°C (68-72°F). This doesn’t provide real cooling in summer, but at least you won’t be bringing additional heat inside the house.
If you’re willing to do a bit of DIY, I would recommend using a storage box (search for Biohort and “Auflagenbox”) instead of an intake shaft to draw the air through.
Why?
- It’s not more expensive than a stainless steel intake shaft.
- The filters available for intake shafts are very expensive and have too little filter surface. As F7 filters, they clog up quickly. In extreme cases (nearby fields plus Saharan dust plus wood stoves all around), this can happen in as little as a week… I now make my own filters from F7 filter fleece that is three times the size of the commercial ones. That works fine. In the storage box, it would be much easier to install several large filters. Cheaper and simpler.
- If you don’t use the smallest box and provide a power connection nearby, it would be possible to dehumidify the air inside the box during midsummer. For this, either install a dehumidifier in the box (something like a Trotec) or even build in a small air conditioner. The smallest units cost around 600 euros and have more than enough capacity to dehumidify the air. This doesn’t actually cool the air, but it reduces humidity inside the house. And 26°C (79°F) at 45% humidity is quite comfortable, while 26°C (79°F) at 75% humidity feels like a steam bath…
Best regards,
Andreas
Thank you for the tips. I’ve attached a plan showing how I would proceed based on the input here.
I’m still considering the intake box—it’s actually not a bad idea.
A quick note about duct routing:
Inside the house, it’s clear—I’m using the insulated duct (MT-R160) from Maico.
For the underground section to the outside air, I would use PVC drainage pipe, with a slope leading toward the utility room.
I don’t necessarily want a geothermal heat exchanger; if anything, I would prefer a brine ground heat exchanger.
Right now, I’m considering installing about 120 meters (390 feet) of brine piping around the house in the utility room. It’s not particularly expensive, and it would prepare me for all scenarios.
Best regards
I’m still considering the intake box—it’s actually not a bad idea.
A quick note about duct routing:
Inside the house, it’s clear—I’m using the insulated duct (MT-R160) from Maico.
For the underground section to the outside air, I would use PVC drainage pipe, with a slope leading toward the utility room.
I don’t necessarily want a geothermal heat exchanger; if anything, I would prefer a brine ground heat exchanger.
Right now, I’m considering installing about 120 meters (390 feet) of brine piping around the house in the utility room. It’s not particularly expensive, and it would prepare me for all scenarios.
Best regards
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