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gringogigante
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# Posted: 7 May 2021 09:09pm
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So I have a small cabin (187sf with 10' ceiling) that I need to ventilate. I know nothin about ventilation. I figured out that I need about 10cfm to be healthy and keep moisture from building up.
I will have a window unit going in the hot months here in Texas.
Anyone recommend a good passive or mechanical ventilation system for such a small space?
I looked at ERV units, but they seem way too big and expensive.
Thanks for any help!
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frankpaige
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# Posted: 7 May 2021 10:41pm
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Not knowing the window configuration? Assuming there is power, because of the window unit comment.
Not knowing about the surrounding tree shading or lack of ( I know, it is Texas)
Is there electrical or is it going to be solar. Air movement is certainly a priority.
What type of roof do you have? And? Is there really moisture build up in Texas?
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gringogigante
Member
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# Posted: 7 May 2021 11:01pm
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Hey there. I will have electricity going to it. There is no shade from trees. It will get hammered in the hot Texas summers (May to November). This is a shed style roof that is west facing. The rear (east facing) wall is 8' tall, and the front (west) wall is 10' tall.
Our climate is very humid and considered to be sub-tropical here in north Texas. My kids and their friends will be spending a lot of time here camping, etc. I am building it with the Zip system that is very water and air tight.
I don't mind putting a dehumidifier in there to mitigate mold, etc. But I'm worried about CO2 build up. It's only 187sf with 9' average ceiling height. So could I just use a bathroom fan to vent? I assume I'd need passive vent holes on one side of the house with a vent fan or ERV on the other side?
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gcrank1
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# Posted: 8 May 2021 10:14am - Edited by: gcrank1
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We are not sub-trop here in sc WI but we do get a run most every summer of hot, humid weather. And Ive spent some time in hard-side campers under beating sun with no AC and no air moving.
I like a topside (through the roof or high in an end gable) outlet for the hot air since that is where it starts to 'stack' from and move downward. To have flow you need an inlet, the lower the better, and pref on a shady or cooler side. Even from underneath where it can be a considerably cooler environment.
Having power is waayyy cool (pun intended). Wow, youve got it made.... A power vent, a small box fan inside moving air across the body, even a tiny AC unit?
Gotta bug/vermin wire the inlet/outlet which reduces the air flow so going bigger on their size is good. Fwiw, Ive found the same true for bathroom vents, when I do the calc and use what they say it isnt enough, I upsize that vent now; works much better.
A double roof with air space between might help? Even if only a pergola style with fabric cover might help keep that direct sun from beating hard on the roof.
Afterthought: If you think about your cabin as an RV you might get ideas. For instance, our last had a Fantastic Fan, a unit that replaces the std RV roof vent with a reversible 3 spd fan. It is 12v but runs off the 120vac to 12vdc RV converter. By being able to set to move air out or in, and the way good cfm's it was the next best thing to AC in our camper. Id use that over a bathroom vent. Should be able to source one, or similar, online (maybe $125ish?)
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Aklogcabin
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# Posted: 8 May 2021 11:08am
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Hello, would an attic vent with a fan built on it help ? The non power one that use the wind. That could maybe help. And help with air movement when you're not there. Good luck
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gringogigante
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# Posted: 8 May 2021 11:43am
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Very good points all! I wish I had HVAC knowledge but I know nothing about them. And with months over 100 degrees, it's a must here.
Is an HVAC not enough? FWIW, I've got a large window unit that is capable of cooling 400sf and the cabin is 187sf.
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Brettny
Member
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# Posted: 8 May 2021 02:28pm
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Are you going to insulate the building? To what R value in the roof?
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gringogigante
Member
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# Posted: 8 May 2021 08:40pm
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No insulation at first. But eventually rockwool throughout the interior walls and ceiling. So an r-value of 3'ish.
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gringogigante
Member
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# Posted: 9 May 2021 02:06am
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Correction:
Sorry for the typo but it's 23-30'ish r-value.
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Irrigation Guy
Member
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# Posted: 9 May 2021 07:43am - Edited by: Irrigation Guy
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Quoting: gringogigante Is an HVAC not enough? FWIW, I've got a large window unit that is capable of cooling 400sf and the cabin is 187sf
An over sized AC unit will not remove humidity effectively. It takes a fair amount time to remove the humidity and an oversized unit will cool the air too rapidly satisfying the thermostat before all the humidity can be removed.
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Brettny
Member
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# Posted: 9 May 2021 08:53am
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Before you insulate I wouldnt bother with trying to run an AC., it's a loosing battle. Just open the windows.
With r20+ in such a small building I would think a 5kbtu should be enough. To big and you wont dehumidify.
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