I never saw a need for them in our 32.7" average per annum rainfall climate.

But here in Raccoon City, animal screens are a must to prevent an incursion of our resident evil.

Rain guards?

Hardly.

Chimney caps to keep out critters and vermin?
A VERY god idea.

I guess I called it the wrong thing. I meant chimney caps, sorry.

We have chimney pots. They do make rain guards for them but we don't have them. What do your chimney caps look like? I have understood them to be mainly to keep birds, etc. from coming in . ..

A clay or copper "chimney pot" is placed on top of the chimney to inexpensively extend the length of the chimney, and to improve the chimney's draft. Today they are decorative.

A "chimney cowl" (also called a cap or shroud) is placed on top of the chimney to prevent birds and squirrels from nesting in the chimney. They often feature a rain guard to keep rain from going down the chimney. A metal wire mesh is often used as a spark arrestor...

A "chimney damper" is a metal spring door placed at the top of the chimney with a long metal chain that allows one to open and close the chimney from the fireplace.

They each have desirable features but none are "necessary".

Here is a link that might be useful: chimney tops

Renovaator, I'm not sure why you think chimney potas are any less functional today that they were in the past. They still work very nicely to improve the draft in a marginal chimney at a fraction of the cost of extending the chimney (and look good too).

While a rain cap is certainly not essential adding one in our house helped a lot with rainwater coming down the flue in heavy storms and bringing a strong smoke odor into the house.

I haven't gotten one yet, but we'll be putting copper and mesh guard/cap on top of our new build's chimney soon.

I'm not wild about the look, but etched into my memory was the day hat we had a sooty swallow fly around in our den for an hour or so back in the 70's before we finally herded it out the sliding glass doors.

Everytime that he touched the walls he left a patch of soot and creosote.... not an experience I'd ever like to repeat!

Our critter guard has a solid metal roof to it, which keeps out most rain (but not all). Critter guard would be my first choice if you can only afford one (critter guard = chimney cap). Otherwise you'll be dealing with freaked out birds, squirrels, and even possibly raccoons at some point. Usually on the most inconvenient day, too.

Does something like this work to keep out rain and critters? Does it hinder proper airflow?

http://www.copperchimneycaps.net/chimneycapscolonial.aspx

Those are some elaborate and pricey copper tops.

After the odour of rotting ravens trapped in a chimney made a house unlivable until nature took its course, I had subsequent installations wrapped in galvanized mesh.