Thermally managed exterior through wall vent

Forums › Home Workshop DIY › Thermally managed exterior through wall vent - for outdoor cabin

Benoire

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#323503 9-Dec-2025 17:01

Howdy folks

Got an external cabin (14m2) which is used for storage and has replaced our garage. The walls are 44m thick timber, with double glazed windows and door seals. As expected, it get hot in there and I'm looking for a way to reduce the temperature. I'm not looking for AC at this stage either.

The obvious approach is some form of vent through the walls that has flaps that close when off that is thermally controlled. I've seen some stuff from the US that does this but looking at something closer to home if possible, and ideally wired to NZ plug.

Anyone got / use anything? Suggestions are very much welcome!

Chris

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#3442051 9-Dec-2025 18:04

While not exactly related to your question, this thread talked about an extra layer to a cabin roof which adds a thermal break to redduce the head radiated into the room from overhead. It may be worth consideration alongside your active cooling plan.

Anyone done a Skillion roof that's airtight and hence no ventilation gap?

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tweake

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#3442052 9-Dec-2025 18:04

put an indoor/outdoor thermometer in there and check what the temps actually. "hot" is very subjective and it also pays to know what the outside air temp is your trying to cool with.

Benoire

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#3442053 9-Dec-2025 18:08

Dynamic:

While not exactly related to your question, this thread talked about an extra layer to a cabin roof which adds a thermal break to redduce the head radiated into the room from overhead. It may be worth consideration alongside your active cooling plan.

Anyone done a Skillion roof that's airtight and hence no ventilation gap?

Yeah mines been constructed like that already - its a colour steel roof on purliins sitting on the roof felt on the original roof boards - there is essentially a ~25mm airgap between the layers and its vented at the point it meets the guttering on both sides... I think it is helping compared to my smaller office cabin but the walls are thicker and its got more surface area to radiate internally.

Benoire

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#3442056 9-Dec-2025 18:10

tweake:

put an indoor/outdoor thermometer in there and check what the temps actually. "hot" is very subjective and it also pays to know what the outside air temp is your trying to cool with.

It will be above 30 degrees given my office cabin is ~26 at the moment and that was with my doors open and fans on. It is going to be getting some homelab components in the rack soon so there will be additional internal heat to dispose of.. I could run an internal AC unit but I'd rather not unless there are no other methods!

tweake

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#3442061 9-Dec-2025 18:18

in my experience, there is not enough temp difference and the airflow volumes are huge to get any decent heat reduction.

but with the sheer lack of insulation due to the skinny timber walls with insulation levels as bad as the windows, your best bet is external shading. stop the solar gain.

pih

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#3442063 9-Dec-2025 18:21

Just a thought, have you considered non-powered automatic ventilation options such as those designed for greenhouses? These are typically designed for opening window vents when it gets too hot. They also come in louvre openers, but these seem to be a little harder to come by in NZ. You may be able to attach one of these to existing joinery, or get your local builder to retrofit another window or two.

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Benoire

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#3442068 9-Dec-2025 18:34

pih:

Just a thought, have you considered non-powered automatic ventilation options such as those designed for greenhouses? These are typically designed for opening window vents when it gets too hot. They also come in louvre openers, but these seem to be a little harder to come by in NZ. You may be able to attach one of these to existing joinery, or get your local builder to retrofit another window or two.

I'm open to any options right now, just trying to find an acceptable solution that doesn't require me spending lots of additional money per month to cool the room using AC... with the windows open (almost opposite sides) its not hot inside as the walls are 'shaded' on 3 sides generally and the roof has a gap between the water proof layer and the roof timber so the airflow is sufficient to remove it down to ambient air temp.

tweake

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#3442170 9-Dec-2025 20:34

what sort of cost is acceptable?

running cost for ac is not much, especially on a small room. i think last time i worked it out it cost me around 20-40 a month for the house. kiwis really overplay the running costs. happy to spend $200 on firewood but not $20 on power. However, the catch is install cost.

timbosan

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#3442171 9-Dec-2025 20:47

Dynamic:

While not exactly related to your question, this thread talked about an extra layer to a cabin roof which adds a thermal break to redduce the head radiated into the room from overhead. It may be worth consideration alongside your active cooling plan.

Anyone done a Skillion roof that's airtight and hence no ventilation gap?

That's my thread :-) I have also made plans for the walls. They are not a thick as the OP's (28mm) but due to the external corner overhangs I can frame up on the exterior with 90x45 timber, add in some 11mm ventilated battens, fills with R2.6 and cover with grooved boards to keep the same look as the cabin. Oh plus the Intello on the external walls beforehand, and Extasana before the battens, keeping it nice and airtight.

Apart from that, look at aircon - there is a portable unit from Jaycar, way cheaper than a standard unit + installation at $650 ish. Thread here https://www.geekzone.co.nz/forums.asp?forumid=141&topicid=323498 If your walls are solid you could cut holes to vent externally and then seal, giving a much better performance than the standard 'in room' units, with less noise.

nzben

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#3442213 10-Dec-2025 06:23

Have a look at this:

https://herbals.co.nz/products/airlift-t14-shutter-exhaust-ventilation-fan-14-temperature-humidity-controller

This is an in wall unit with shutter system. They have smaller and larger sizes (= volume throughput - this one does about 43m3 per min), if you look at the S series that is more of a manual controller, if you look at the T series it comes with a Wifi/Bluetooth module that allows remote app control and programming and comes with a temperature and humidity probe. With this system you can setup so it will ramp the speed as the temperature changes to maintain the set temperature.

Its a American brand and very good, these guys are an Auckland based hydroponics shop that happens to import the product, good prices for the quality and features.

I put a 8" system in to a 18m2 sleep out and it expels a lot of hot air, however if I did it again I would get a higher capacity model like this one. You can also get inline versions of the fans if you want to do it ducted.

We also set up a sail cloth to keep direct sun off the ranch slider glass and that makes a big difference.

nzben

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#3442214 10-Dec-2025 06:25

Also if you do install a fan (up high) you will want to install an inlet (down low or in floor preferably on the shaded side of the building) to allow cooler air to be sucked in while the hot air is expelled

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Benoire

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#3442219 10-Dec-2025 07:39

nzben:

Have a look at this:

https://herbals.co.nz/products/airlift-t14-shutter-exhaust-ventilation-fan-14-temperature-humidity-controller

This is an in wall unit with shutter system. They have smaller and larger sizes (= volume throughput - this one does about 43m3 per min), if you look at the S series that is more of a manual controller, if you look at the T series it comes with a Wifi/Bluetooth module that allows remote app control and programming and comes with a temperature and humidity probe. With this system you can setup so it will ramp the speed as the temperature changes to maintain the set temperature.

Its a American brand and very good, these guys are an Auckland based hydroponics shop that happens to import the product, good prices for the quality and features.

I put a 8" system in to a 18m2 sleep out and it expels a lot of hot air, however if I did it again I would get a higher capacity model like this one. You can also get inline versions of the fans if you want to do it ducted.

We also set up a sail cloth to keep direct sun off the ranch slider glass and that makes a big difference.

Thank you, I had seen these on Amazon and its good you have experience of them as sometimes they can be hit and miss... This is what I had been thinking so will take another look. I was planning on installing a above the floor on the shaded side as well to draw air in... even yesterday when it was hot, the air in the shaded side was cool enough that it would do enough.

mdf

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#3442253 10-Dec-2025 11:46

You mention windows. Can you fix these open securely to allow a through draft? As per a previous post, ideally low(er) on the cool side and high(er) on the warm side.

Passive methods to reduce the heat coming in can work really well too.

What colour are the roof and exterior walls? Could you paint these a colour with a high LRV?

Can you fit reflective solar film, external awnings, or even internal venetians on the sunny windows?

A ceiling fan works to reduce how you feel in the room, but won't actually reduce the heat so if you're worried about kit overheating, that won't cut it.

nzben

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#3442311 10-Dec-2025 12:47

Benoire:

nzben:

Have a look at this:

https://herbals.co.nz/products/airlift-t14-shutter-exhaust-ventilation-fan-14-temperature-humidity-controller

This is an in wall unit with shutter system. They have smaller and larger sizes (= volume throughput - this one does about 43m3 per min), if you look at the S series that is more of a manual controller, if you look at the T series it comes with a Wifi/Bluetooth module that allows remote app control and programming and comes with a temperature and humidity probe. With this system you can setup so it will ramp the speed as the temperature changes to maintain the set temperature.

Its a American brand and very good, these guys are an Auckland based hydroponics shop that happens to import the product, good prices for the quality and features.

I put a 8" system in to a 18m2 sleep out and it expels a lot of hot air, however if I did it again I would get a higher capacity model like this one. You can also get inline versions of the fans if you want to do it ducted.

We also set up a sail cloth to keep direct sun off the ranch slider glass and that makes a big difference.

Thank you, I had seen these on Amazon and its good you have experience of them as sometimes they can be hit and miss... This is what I had been thinking so will take another look. I was planning on installing a above the floor on the shaded side as well to draw air in... even yesterday when it was hot, the air in the shaded side was cool enough that it would do enough.

You need the ability for the air drawn inside to be expelled (fan sucks air in) or the air sucked out to be replaced. (fan sucks air out) Either a passive vent or open windows. My research into ventilation is that it is more effective to draw out air and have it replaced rather than force air in - ie, fan draws the hot air out, and let cool air come in via a vent / windows.

I have had an AC affinity fan running in our attic space drawing air out via ducts for about 3 years now and no sign of faulting. I think the fans are rated for around 6-7 years of 24/7 use.

Benoire

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#3442458 10-Dec-2025 17:34

nzben:

You need the ability for the air drawn inside to be expelled (fan sucks air in) or the air sucked out to be replaced. (fan sucks air out) Either a passive vent or open windows. My research into ventilation is that it is more effective to draw out air and have it replaced rather than force air in - ie, fan draws the hot air out, and let cool air come in via a vent / windows.

I have had an AC affinity fan running in our attic space drawing air out via ducts for about 3 years now and no sign of faulting. I think the fans are rated for around 6-7 years of 24/7 use.

The 'plan' was to use a mechanical fan placed near the centre roof beam venting the heat and then using a series of simple vents on the shaded side at the bottom to allow the exchange of air. I'm just trying to vent the excessive heat that is building up in the apex of the roof area that causes the rest of the cabin to overheat... touching the felt below the colour steel, it doesn't feel amazingly hot to touch.. If it doesn't work then AC in summer using the same vent outlet would work - just more costly!

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