Construction Design-Humidity Control in a Garage

I watched an electrician install two ceiling fans in an attached garage recently while I was working as a subcontractor on a new home being built.  I quizzed him on their use and he said moisture control.  This got me thinking about controlling humidity in a heated garage in a northern climate, this week’s topic.

Humidity condensing on a window.

Let’s start with what is happening in a heated garage in a cold climate.  If it’s used for vehicle storage, very cold vehicles, possibly packed with ice and snow enters the garage.  Hopefully the garage has a floor drain where most of the melting ice and snow will leave the structure. (Some don’t).  Some of this moisture will end up in the air, raising the humidity level within the building.  If the garage is attached to a home, some moisture will end up inside the home, some will condensate on cold surfaces such as windows or metal parts of the garage entry or overhead door, some may end up in the attic or wall assemblies by way of air leaks in the air control barrier.  Most garages don’t have the same air sealing details as home.  There are a few methods that will help moisture control.

Run a dehumidifier.  I see this often when conducting energy audits.  A dehumidifier will probably run continuously in a garage during the heating season.  Most dehumidifiers use between 350 and 500 watts per hour to operate, costing as much as $50 per month to operate in my area.  They do work well, but there are other methods that can also affectively remove moisture.

Exhaust only ventilation.  I’m not a fan of this type of ventilation for a home, but in a garage, it will work.  Exhausting conditioned air out of the building will be replaced by air from outside the garage, most likely from around the overhead garage doors which typically have less effective weather stripping than the typical entry door.  (Just the nature of the average garage door).  Of course, removing warm air and replacing it with outdoor air during the winter will elevate heating costs.  I would install the fan on some sort of humidity sensor and choose a fan that has a variable CFM rate.  There may be times during the winter where the ventilation rate may need to be adjusted.

A small HRV unit.  I wrote an article a while ago talking about heat recovery ventilators.  Read that article here.   Manufacturers do have low CFM HRV’s designed for small homes that would work well in a garage.  A couple of drawbacks are the cost to purchase and install and possibly the air quality within the garage.  Many garages double as a workshop, producing dusts.  Filters may need to be cleaned more often.  On the plus side, most HRV’s I have tested for their electrical usage are consuming around 100 watts, a quarter of what a dehumidifier will use.  Again, I would use some sort of humidity sensor to control the HRV.

A heat recovery ventilator.

I recently discovered the Lunos brand of HRV’s and ventilation equipment. Lunos is a German company that manufactures energy efficient ventilation systems.  The Lunos e² is a pair of wall installed fan assemblies that contain a ceramic heat exchanging core.  One fan exhausts air from the space while the second fan intakes an equal amount of air from outside.  The ceramic core is heated by the air exhausting the space, after 70 seconds, the two fans switch their rotation.  The former exhaust fan with the warmed ceramic core becomes the intake fan.  The stored heat is then removed from the core and is delivered back into the room.  Every 70 seconds, the pair of fans reverse their rotation, the heat recovery efficiency is listed at 90%.  The listed CFM rate is 18, not a lot of air movement, but the continuous operation should create enough ventilation to reduce humidity.  Of course, the size of the garage and moisture load will determine the ventilation need.  Any filters associated with this system may have to be changed or cleaned if the garage doubles as a workshop.  More information about the Lunos e² can be found at  This type of HRV would also work great in a small home.

A Lunos e² HRV.  Sold in pairs, one will exhaust while the second supplies fresh air to the structure.

In the beginning of this blog, I talked about the electrician installing a ceiling fan to “dry” the garage and how that got me thinking about an alternative solution.  What were the two ceiling fans (or any air moving fan for that matter) accomplishing?  They were mixing the water vapor evenly in the air within the garage.  (This would have happened naturally given enough time, the fans speed the process.)  The floor and vehicles were dry after a period of fan operation, the moisture was changed from liquid form to vapor.  The elevated humidity level would only be reduced when a door in the space was opened, if enough natural air leaks are present (moving all that moisture into a wall cavity or roof assembly where it may condense), or if any of the methods discussed in this blog post were used.

Anytime we are dealing with moisture within a home (or garage), stopping the moisture before it enters is always the first choice, removing the moisture, which requires energy, is second.  Unfortunately, a garage is a space similar to a bathroom, moisture is going to be present.  How that moisture is dealt with can have an affect on the durability of the structure.

2 Replies to “Construction Design-Humidity Control in a Garage”

  1. I live in middle TN and have a detached garage and I’m noticing mold on some wood furniture being stored. The garage is NOT heated as our winters are typically mild but we have lots of humidity in the summer. Do you think an HRV system would work for my situation, or based on my conditions would something else be more appropriate? Thanks for allowing questions. I look forward to a reply.

    1. Hi Jennifer, HRV’s work best in cold and very cold climates. Your live more in a mixed climate where ERV or energy recovery ventilators are much more common. The issue with both HRV and ERV’s is the cost, quite expensive to purchase and install and when operated during the summer, they tend to bring the outside humidity inside. A dehumidifier might be your best bet, but even a good dehumidifier might not keep up if the garage isn’t air sealed well. Really tough to air seal a garage with the big, typically air leaky garage doors. Is the garage finished or just a shell with bare framing and an open ceiling?

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