Window fogging.

Your windows are fogging because the raindrops evaporate as they plummet through the air, saturating it with water vapor so the humidity level is very high. Plus, as you move forward your windshield is cooled by the convection of outside air over its surface. So if you blow that humid air over the inside of the windshield, and the windshield is cooler, it is going to cause condensation -- fogging.

A/C will dry the air out so that you get evaporation on your windshield instead of condensation. This is why hitting the "defrost" button on your climate control panel will automatically engage the A/C in non-ECON mode.

I'm seeing this problem a lot more in OR (wet, humid, cool days) than I did in MA (very cold but also very dry days). You can see its opposite if you run your A/C too cool down in the South of the U.S. during hot and humid summer days, where your cold interior causes condensation on the exterior of the windshield.

Heating the air causes the relative humidity to decrease. Warm air alone should defog your windows if there were no added source of humidity in your car. Unfortunately when you get in your car you add: your breath (very humid) and your wet clothes/bumbershoot/dog/golf clubs/passenger/whatever.
That said I have noticed this (the need to run the A/C in order to defog the windows during rain) much more in the Insight than my previous cars. I thought it might be related to the relatively small cabin space.

Yes I understand, but this is the first car ever who has this problem. All of my other cars didn't have a/c, and I never had this before on them, is it likely that the Insight ventilation is not sufficiënt enough ?

I've noticed it on other Hondas aswell ( 89' CRX Si, US-Spec/ 97' Civic, 90 HP) both had air-con. Seems to be a "Honda-problem", nothing to worry about :wink:

dan said:

Heating the air causes the relative humidity to decrease.

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Yes, but the problem is that near the windshield the air is cooled back down, and this is often enough to result in condensation on the windshield inner surface, even if you are not breathing on it.

True, Tim. But it has been my experience that in most cars that a significant portion of the foreword windows can be kept fog clear with heat alone if 1)the outside temp is above freezing and 2)the occupants’ clothes are dry.
Then again, if Corvallis is where you are from originally, I will have to differ to your expertise. I could only make it in Eugene for 2 years before I moved back south.

Does the fogging problem also exist on the non-a/c Insight models ?

Well from what I have seen fogging is a problem in the insight... it fogs up all the time especially in humid weather.... the only way around it is to use the defrost which if kept on takes away idle stop... bit of a pain I think..

meow77 said:

.... the only way around it is to use the defrost which if kept on takes away idle stop...

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Try hitting the ECON button so that the climate control panel reads A/C ON ECON (instead of AUTO) and then hit the MODE button until you see the indicator showing airflow out the defroster and floor vents. That can sometimes give you enough defrost and A/C activity to keep the windows clear, and won't prevent idle-stop so long as the outside air isn't too cold.