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I will be installing a Rennai gas direct vent wall heater. The thru the wall vent wants a 3 1/8 hole. Exterior is vinyl siding. It doesn't come with an exterior wall shield and Im not wild about screwing it right to the siding. I could use a vinyl mounting block...but it's vinyl...What else could i use? The direct vent exterior shields Ive used on the gas fireplaces were metal and had a 6 or 8 inch hole, much too big for the 3 inch vent. Any I wrong to be concerned?
Here are installation instructions:https://media.rinnai.us/salsify_asset/s-6e9d8980-5562-48b7-8345-766061d17682/200000073-EX17CT, EX22CT
Cut and paste all the above