Should I install furnace vent screens?

[EightFingers]

Right now the furnace has just the two pipes outside the house, one intake, one exhaust. There are no covers or screens for these.
I see they can be purchased, but I also see that they are not recommended as they restrict airflow. Of course a wasp nest will restrict airflow too! 
I saw one outfit that has a kit where you have to change out the screens twice a year which I don’t like as it’s just one more thing for me to remember(forget).

[blackhat]

A couple things, if it’s not stainless or plastic, flue gas will turn it into rusty junk real fast.  

Frost can build on the screens in the right conditions. That will shut the equipment down. 

We have different and probably fewer bugs than you but they are seldom a problem. I’ve never seen wasps build nests in vents. 

A pre season check and quick cleanup with a shop vac and an old paint brush is all that’s necessary.

[EatenByLimestone]

I’ve treated thousands of wasp nests and never seen one in the intake or exhaust of a furnace. Around the opening outside the pipe in the sill plate, yes, but in the furnace, no. It certainly could happen, but it’s not common. Probably less so if it’s used for heating water all year round.

I did have one in a vented fireplace one though. I didn’t think that it might have a pilot light. When the pilot lit off the propellant in my fogger, hoo boy!

[meackerman]

if you really want to install screens, couldn't you use an appropriately sized adapter to increase the size of the pipe up one size and install the vent on the large size?

Seems it shouldn't restrict the air flow with the larger size pipe.

[blackhat]

The screen itself isn’t the restriction. It’s the stuff stuck to the screen that builds up and chokes it.

[Snipe Hunter]

I wouldn't install screens. I see issues where home owners think they're dong the right thing and causing other issues when in fact they are restricting flow. High efficiency furnaces need good, unobstructed flow. Bigger exhaust vents are different where birds can nest.