We have a Navien on demand water heater. The intake and outlet vent pipes run out through the poured concrete foundation and have a plastic grill on the end. If the intake vent is blocked in any way the water heater will not turn on as a safety feature.

I have to add another tighter mesh over the intake in the summer or paper wasps build nests inside the pipe. If I leave the mesh on then in the winter it gets blocked with snow and ice.

I need some sort of vent cover that blocks insects and does not get blocked by snow. Here is a sample with the "as delivered by the contractor" on the right and with a crude but workable filter for summer use on the left.

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Any ideas?

Edit: the manufacturer suggests adding a PVC T valve at the end of the outlet. The number of elbows allowed is governed by the length of the run and number of previous elbows in the run. I'm going to try a T valve and the filters shown in the answer below.

  • Is this vent the concentric type where the hot exhaust comes out the center of the vent and cool intake air enters around the outer part of the vent?
    – Michael Karas
    Dec 15, 2013 at 19:33
  • There is an outlet and a separate inlet so no chance to heat the intake air with the outlet. Good idea
    – kevinskio
    Dec 15, 2013 at 22:28

2 Answers 2


Aside from adding an elbow, one method to allow finer mesh without blocking airflow is to extend the mesh a fair distance - I'll try to get a picture of Something similar, but doubt I can find the exact thing I'll want - basically either a long (12"/30cm or so) mesh tube, or a 12-18" section of pipe, drilled full of holes, and then wrapped in mesh small enough to keep the wasps out. When you make the mesh smaller, you need more area so that the flow can remain the same (even if some parts are blocked) - so the idea is to greatly increase the area of mesh.

OK, these are fish pond filters, but they have the right idea.

fish pond filters

Some car or truck air filters might actually be adaptable to work, too - especially the "aftermarket high flow" types (you might ditch the "foam filter" those have and just use the "mesh cage" part of them) - but that's more if you want something you can buy - you should be able to make something that works out of ordinary hardware cloth mesh.


Picture of the vents would help. The way I've usually seen them installed is with a 90deg elbow on the intake so that it points down. That would prevent snow from clogging it.

The exhaust vent pipe usually has a 90 deg elbow so that it points up. You can get a rain cap for the end of it to keep rain/snow out.

Looking at this document from your manufacturer it shows one of the vents elbowed to face down like I indicated the other one isn't.

After seeing the pictures of your vents it looks like you can elbow the one on the right and then get a hooded cap for the one on the right. Something like the Noritz PVT-HL looks like it might work.

Then you can install a tighter mesh to keep the wasps out.

By the way, have you tried those wasp deterrents that look like nests? I haven't but they seem to have good reviews.

  • picture is up, I did try the wasp nests but those seem to work best for yellow jackets not the paper wasps we had issues with.
    – kevinskio
    Dec 15, 2013 at 19:01
  • Thanks. Right picture looks like you can add a PVC elbow, maybe short section of pipe and finer mesh over that. Left picture it's hard for me to tell with the screen over it. It doesn't look like PVC pipe. Maybe you can take a section of large diameter pvc coupling, cut it in half to have 2 U shapes and some how attach it over it to make a little snow roof? P.S. check with manufacturer to make sure the elbows covers won't cause problems to be safe. Dec 15, 2013 at 19:09
  • If the vent is the typical concentric type for direct vent heaters the hot exhaust exits a center pipe and intake air enters around the larger diameter outer pipe. The intent is that the intake air helps to cool the exhaust pipe and isolates the hot pipe from the siding / sheathing / framing to prevent fires. This type of vent will be rather hard to be attaching PVC elbows and what not.
    – Michael Karas
    Dec 15, 2013 at 19:37
  • Looked at this install guide and it only shows one vent elbowed. aceee.org/files/pdf/conferences/hwf/2009/… also found this product that looks like it would work for the left vent to protect from snow and allow a finer mesh to be installed. the-wholesale-warehouse.net/servlet/the-509/… Dec 15, 2013 at 19:40
  • @MichaelKaras he has 1 heater and 2 pipes so it's not a concentric pipe. Dec 15, 2013 at 19:42

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