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We have a furnace for heating our home and the chimney cap lets the rain into the home. Which cap do you recommend for this issue although this cap seems very popular.
You can get a chimney cap at the big box home improvement stores----or perhaps better, a roofing specialty/shingles supply dealer------the most important thing is to get a STAINLESS STEEL chimney cap---before you go to the store you have to go up on the roof & measure the firebrick chimney liner length & width that juts out from the rest of the chimney so that you can buy a stainless steel unit that fits right over the dimensions of the firebrick; don't ignore internet sources for a CC that may offer a good price, free shipping & no sales tax.
There are usually bolt holes at the base of the CC so that you can firmly secure it to the chimney----even better is to find a CC whose base fits tightly INTO the flue liner (bring your measurements with you to the store)---this is probably the most secure way of attaching to the chimney---there will always be the occasional gale winds as the months & years go by that will blow the CC out into the next door neighbor's yard if you don't secure it firmly.
If the CC doesn't appear to be good & secure after installing, you can always drill some holes in the exterior brick with a masonry drill bit, epoxy them into the holes & attach to the CC with insulated heavy duty copper wire (ordinary romex electrical cable is excellent) to prevent rusting---don't succumb to the temptation to spend a few dollars less on a regular STEEL CC---the regular steel CC will only rust out in a few months & leave an ugly large brown rust stain on your chimney, your roof shingles, & your house siding.
Safety First: Always wear rubber-sole shoes when going up on a roof; never work on a wet roof, or when it's windy; always attach a heavy rope to your waist & then to the chimney or other secure point to prevent falls.
Are there some furnace chimney caps that would NOT allow the exhaust to leave the furnace due to not enough free net ventilation and could return the exhaust back into home?
Thanks very much
No, the vent area of chimney caps are specifically designed to prevent this.