What prevents cold air from coming in through evaporative cooler

Question

I have an evaporative cooler mounted to my roof. The air comes straight down through a large vent in my living room. During winter, I wondered if cold air could come down through that large vent, but I could not feel any coming in (just put my hand next to the vent). I did not do anything to cover/seal the vent for the winter. Now that I am using the evaporative cooler again for the hot temps, I was reminded of this question.

Do evaporative coolers or the air ducts they use have a common mechanism for preventing air from flowing when they are off?

Answer 1

The evaporative coolers that sit on roof are normally serviced in the fall at the end of the usage season. Typical service includes shutting off the water supply to the cooler, draining the water sump in the cooler, cleaning away any debris and leaves that may have accumulated around the unit and then installing a cover over the whole cooler shroud. The jacket may be a canvas or tight wave synthetic fabric material.

These covers are typically available at home centers and evaporative cooler suppliers and have to be purchased by size. They are typically sewn as a fitted cover that then has a closure along one side that is cinched up with heavy cord similar to lacing a shoe. Some covers have a draw string in a hem around the bottom that allows the cover to be cinched down under the lower edge of the cooler shroud to prevent it from being blown off in strong winds.

Since evaporative coolers are typically used in areas where there is intense sun for large parts of the year be prepared to have to replace the cooler cover every few years.

Answer 2

As it seems evident that you did not cover the cooler in the winter as described by Michael and Jim, I would venture to guess that warm air you heated going up the vent prevented any noticeable cold draft coming in there - there are probably plenty of other gaps lower down on the house providing fresh cold air for your heating system to heat and send up the cooling vent during heating season. In general, this is "stack" or "chimney" effect - warm air rises - without the cooler running and blowing cool damp air down the vent, warm air from the house rises up through the vent, if the vent is not closed off.

It's possible (but evidently not likely or common) that your vent has an automated damper on it, which would save you some heating money if you do not close off the evaporative cooler from above in winter.