One important thing to remember when it comes to installing a chimney cap on your own is to remember to wear protective gloves! Often times,
stainless steel or other metal chimney caps have extremely sharp edges. Similarly, if the chimney cap you have purchased has instructions from the manufacturer, those should be followed instead of any other procedure. If you are going at it alone, you’ll have to first take measurements for it. An important measurement that people always forget about, whether they are measuring to install a single flue or multi flue cap is the height of the tile that sticks out of the chimney. If it is very tall you may need to make special arrangements ot have a height extender installed.
If you have only one flue in your chimney then you will simply measure the dimensions of the flue at the top of the chimney. If you have more than one flue in your chimney you will need to decide whether to have two single flue caps or one multi flue cap. Two single flue caps are appropriate for when the two flues are located far enough apart that two single flue caps will fit side by side without having to be bent. If your flues are located to close together then a multiflue cap, which screws into the crown itself and covers the area over and surrounding the two flues would be more appropriate.
After taking measurements and ordering your cap, you will need to install it properly in order to prevent having to keep reinstalling a cap that has blown off in the wind or having to buy a new cap if it blows off and gets damaged. For a single flue cap all you will need to do is place it over the flue and screw the screws in to tighten it on. I always recommend applying a thin ring of silicone for the cap to sit on. This will prevent it from blowing off in strong winds. If you are installing a multi-flue cap you will need to screw it directly into the crown. I recommend using a thin ring of silicone again to ensure that the cap does not come flying off. Multi-flue caps are usually custom made and can get expensive, especially for very large sizes. You don’t want to have to purchase two of them if one falls off and is bent beyond repair.
Band around caps are a less utilized option for multi-flue caps. Instead of screwing this cap into the crown, they actually “band around the top of the chimney.” Measure the outside dimensions of the top row of all four sides of the first row of brick . Make sure these are exact! This cap will actually fit around these brick snugly and you attach them with screws.
One final note, I do not recommend using black painted galvanized steel or aluminum covers where oil or coal is being burned or wood/pellets are the primary source of heat.