Passive Garage Ventilation Options

[oleblue]

Hey guys, I have a 40 x 100 shop house with 11' walls where 65' is my shop and the other 35' is my living quarters. The shop is separated by very well insulated sheetrocked walls and spray foam. Located in Arkansas.

The building is a red iron frame and is roofed and sided with structural insulated panels that are 3.5" thick. This is my first summer in the place, I bought it last summer. I noticed that on my sheetrock walls separating my living quarters, I have little round circles of mildew starting to form.

There is no ventilation to the outside in the shop portion. No louvers, exhaust fans, ridge vents, nothing. My guess is the humid stagnant air is causing the mildew to form. I would like to install some type of passive ventilation system that would get some air moving through the shop.

I'm thinking of installing a couple of these roof vents to exhaust the hot air. https://www.gaf.com/en-us/products/master-flow-high-capacity-dome-vent-hcd144

And a gable louver and a wall louver for the air intake since ridge and soffit intakes are not an option. What do you guys think?

My concern is
1. would this be enough to actually create some type of airflow in the shop to reduce moisture/stagnant air or is there a better passive option?

2. When I am heating the shop in the winter, it seems that all my heat would rise to the top and escape the vents. So I would have to have a way to block them off in the winter. Any thoughts?

 

[wssix99]

I have a HRV (Heat Recovery Ventilator) in my highly insulated ICF garage.

View media item 63233

It's wired to my garage door lighting circuit, so it runs 10 minutes (with the stock lighting) after the garage door is opened/shut, which is enough to solve for my carbon monoxide ventilation requirement. You can also hook up a humidistat or differential control to move the air at other times.

In the winter, I keep the stock heat exchanger in. In the summer, I take the heat exchanger out and and put in some flat sheet metal panels to hold the filters. This allows me to send the hot air out instead of trapping it in, like the HRV is supposed to do in the winter.

 

[Hank11]

A dehumidifier (or two) and a box fan will fix this. Not passive but lots better, and still not expensive to buy or run.

 

[TWD puller]

I have a HRV (Heat Recovery Ventilator) in my highly insulated ICF garage.

View media item 63233

It's wired to my garage door lighting circuit, so it runs 10 minutes (with the stock lighting) after the garage door is opened/shut, which is enough to solve for my carbon monoxide ventilation requirement. You can also hook up a humidistat or differential control to move the air at other times.

In the winter, I keep the stock heat exchanger in. In the summer, I take the heat exchanger out and and put in some flat sheet metal panels to hold the filters. This allows me to send the hot air out instead of trapping it in, like the HRV is supposed to do in the winter.

I am getting ready to build a ICF shop. How do you like yours?


Sent from my iPhone using The Garage Journal mobile app

 

[nadogail]

Sorry but, I am not an HVAC Professional.

The GAF vent in your question may well be a good choice.

 

[matt_i]

Ceiling fans? Ideally hang them down about 4ft from the ceiling. Stirring air can't condense unless its actively raining or you brought in something thats at -40F lol.

 

[PWilks]

Are your walls insulated in the shop?

the largest issue is you have SIPs for roofing structure, but if the walls aren’t insulated, you have all the hot air stuck inside your shop.

Ridge vents would probably be the easiest way to deal with the issue. Ceiling fans are your friend.

If the walls aren’t insulated, I would consider that (people say insulation doesn’t help if you don’t condition). The thing is, I’ve insulated my attached, non conditioned garage, and there was a 15 degree difference throughout the summer, compared to when it wasn’t insulated.

 

[yeldogt]

So ... let me understand.. You have a nice tight building -- holding the outside climate at bay ..... to solve your problem you wish to punch a bunch of uncontrolled holes in it to get what you paid to keep out .... in?

Tight buildings -- are tight. Any moisture inside will stay there. That's why with a tight building on a slab -- you must have a VB under the slab or the slab will constantly give off moisture to the inside. You have two issues with tight building -- the need to refresh the space for safe breathing and living and at times the need to remove excess moisture from the building. This moisture comes from people all the time and from outside when humid.

No matter how tight a building is -- it still leaks. I find the best way is to introduce outside air pressurizing the space ... You can use an HRV/ ERV. I typically use a simple system using a dehumidifier that's capable of being ducted and controlled -- it brings air in direct through the unit. The fan in the dehumidifier is tied into a vent to the outside -- it cycles a damper that brings in outside air based on preset cycle. Other times it's available to dehumidify the space .The need for make up air in a building is dependent on the number of people and the activity.

How much AC do you need ? Often if the AC load is high enough ---- it's also enough to remove the moisture -- you want to get it to the 45 -50% mark.

When AC loads are low and it's humid inside/outside .. you need a dehumidifier.

 

[wssix99]

I am getting ready to build a ICF shop. How do you like yours?

It's great. It does EXACTLY what it's supposed to do and is perfect at keeping heat in. (Hence this thread and some of our other threads on the topic.) In Florida, you'd need some "smart" electronics to control your ventilation or a heat pump to cool the space - otherwise it will turn into an oven. One issue is that the walls constantly radiate heat for the average daily temperature. The second issue is that every time one brings a car into one of these garages, an enormous amount of heat comes in with the hot engine. As the engine cools, it heats up the garage - and that heat can't get out.

Here are some more threads on the topic and ICF garages. In particular, Firebrick has a great one:
https://www.garagejournal.com/forum/showthread.php?t=381799
https://www.garagejournal.com/forum/showthread.php?t=362535&highlight=pour
https://www.garagejournal.com/forum/showthread.php?t=337783&highlight=firebrick+icf&showall=1