Interior vent flanges act as a collar around vent ducts.
Hollow wall coverings, such as drywall, won't securely support a water heater's vent flange fasteners. Common mounting solutions including installing lumber bracing behind the drywall, securing the screws with hollow wall anchors or gluing the flange to the ceiling with a construction adhesive. If your flange provides bracing for the vent duct, you must support it with blocks installed between the ceiling joists. If the flange is only a decorative accessory, you can opt for hollow wall anchors or adhesive. In either case, installing a ceiling-mounted flange requires only common tools and basic construction skills.
Instructions
1. Set the compass or drywall circle cutter's gauge to the radius of the vent flange's opening; the opening's radius is half of its diameter. Place the compass or cutter pin at the center of the opening's desired location.
2. Turn the compass or cutter one full rotation to lay out the flange opening's perimeter. If you used a compass, cut out the circle along the layout line with a drywall saw. If you used circle cutter, score the center of the circle into wedges with a utility knife and knock out the circle with a hammer.
3. Access the attic above the hole. Measure the distance between the joists or trusses that surround the hole. Mark the distance on two pieces of framing lumber and cut the lumber to size with a circular saw. These pieces run between the joists on either side of the hole to provide a fastening surface for the vent flange.
4. Determine the allowable proximity of the lumber to the vent duct. Many vents require a minimum clearance space between the duct and framing materials or insulation. Refer to your water heater manufacturer's instructions to determine clearance dimension. Fasten a lumber block perpendicular between the joists with a framing nail gun, one on each side of the hole, according to the clearance requirements. Measure the sides of the blocks that face the hole.
5. Mark two pieces of lumber at the distance between the blocks and cut the lumber to size with a circular saw. These pieces will run between the previously installed blocks, parallel to the joists, and form the remaining sides of a box that provides fastening surfaces for all four sides of the flange. Fasten the recently cut blocks perpendicular between the existing blocks, one on each side of the hole, according to the clearance requirements. Mark the blocks' position on the ceiling's exposed surface; the blocks' locations are concealed during installation.
6. Slip the vent flange over a piece of vent duct. Mount one end of the duct over the preceding length of duct or the heater's outlet. Push the remaining end of the duct through the hole in the ceiling. Slide the flange up the duct's shaft and flush against the ceiling's surface. Attach a driver bit to the power drill. Align the flange's base square with the marks that represent blocks' locations. Drive screws through the flange's base with the power drill. Apply a screw to each corner and every 3 to 4 inches along the perimeter.
Tags: between joists, distance between, side hole, vent duct, vent flange, according clearance