Central Heat and Air
Central heating and air conditioning systems should be installed by licensed professionals. There are various steps that you might be able to do, however, without bringing in a contractor. Materials: measuring tape
tin snips
metal-scribing compass
sheet-metal ductwork in different sizes
sheet-metal for creating air return boxes and caps
air return grill
floor registers
stud sensor
reciprocating saw
dampers for takeoffs from the main duct
ductwork insulation
flexible ductwork tubing
sheet-metal crimping tool
drill, with drill bits, driver bits and a long wire bit
self-tapping sheet-metal screws
metal straps to support ductwork
circuit breaker box with 220-volt breaker
flexible electrical conduit
exterior-grade electrical cable
flexible gas tubing
central heat and air unit
work gloves
safety glasses
breathing protection Steps: - One of the first things you'll need to do when installing a new air conditioning system is to locate and mark the areas for new vents, also known as registers. When positioning the registers, keep in mind that they should be set on exterior walls when possible, six to eight inches from the wall and in an area where furniture is unlikely to be placed.
- Each register should also be placed next to, not directly over, a floor joist. To locate the floor joist, use a drill with a long, rigid, straight wire (such as a coat hanger wire) to drill through the floor in the area where you plan to place the register. From beneath the floor, locate the wire and measure the distance to the closest floor joist. Then transfer the measurement upstairs, mark the placement of your register, and cut out an access hole using a reciprocating saw.
- Next, you'll need to install the return air ducts and grill. You'll need to cut a hole in the floor near a non-load-bearing interior wall (preferably inside a closet, where the air return box will be less noticeable) for the air return ductwork. Then use the back of the return air grill as a template to mark the wall. Before cutting out the hole for the grill, cut a small hole in the wall to check for plumbing or electrical wiring. When you're sure the area is clear, use a reciprocating saw to cut out the hole for the grill. Finally, box the area in with a sheet-metal box ( figure A--see above) and attach the return air grill to the wall.
- After you have the holes cut for the registers and air return, you're ready to work on the main trunk line, which supplies the air to the ducts. The main trunk line is made of sheet-metal ductwork. This ductwork is typically shipped in flat sheets rather than cylinders; however, you can easily bend it into a cylindrical shape and fasten the sides together to form ductwork tubing (figure B). To create a long piece of ductwork, crimp the top of one tube and insert it into the bottom of another tube (figure C); then line up the seams, secure the connection with self-tapping sheet-metal screws, and wrap the joint with duct tape.
- When the main trunk is long enough, you can begin cutting the "takeoff" holes to supply the registers. Measure the locations of the registers, and transfer the measurements as closely as possible to the main trunk. Then use a metal compass to scribe a circle at each takeoff point (figure D). Use a sheet-metal hammer to knock a hole in the middle of the circle, then cut out the circle with tin snips. After all the holes have been cut, wrap the trunk with ductwork insulation.
- Create takeoffs to fit in the holes in the trunk. Use short pieces of ductwork that are narrower than the trunk and cut tabs into one end. Fold every other tab outward at a 90-degree angle; then fit the straight tabs into the takeoff hole. Then fold the straight tabs over so that they clamp the takeoff in place (figure E ). Use duct tape to secure the takeoff, and use aluminum tape on the inside of the joint so that it's as airtight as possible.
- Install a damper in each takeoff to regulate airflow (figure F). Then wrap the takeoffs with insulation, being sure to leave the damper handle exposed.
- Use metal straps to hang the main trunk under the house (figure G). Attach flexible ductwork hoses to the registers, and extend them to the appropriate takeoffs. Slide the hoses over the takeoffs and secure them with duct tape.
- Pour a concrete pad outside for the main unit to rest on. Allow the concrete to dry thoroughly, and set the unit in position.
- To attach the supply and return fittings to the unit, first cut a round hole in one of the caps for the back of the unit. Then create a large takeoff vent similar to those used on the main trunk, and secure it in place with the tabs (figure H ). Attach the flexible ductwork to the takeoff and secure it with duct tape ( figure I).
- Establish a connection from the main circuit breaker to a secondary breaker box near the unit (figure J). Run a power supply through flexible conduit from the secondary breaker box to the unit. Then connect the gas line (if applicable) to the unit, and attach the drain line, which drains condensed water from the cooling coils.
- Since you're changing out your air conditioner, it's probably a good idea to get a new thermostat, too. Many modern thermostats can be programmed so that the air conditioning system operates only at specific times of the day. In some cases, thermostats may be provided with the air conditioning unit.
- To set the airflow at your registers, you'll need a velometer (figure K ), which measures air velocity in feet per minute (fpm). Take four readings across the face of the register to determine the average velocity. In most cases, your registers should be producing about 700 fpm for large rooms and 400 fpm for bathrooms and other small rooms.
Hints: - If you're replacing an air conditioning system, there's a good chance you'll need to tear out the old system first. There may be special requirements in your area for disposing of building materials, so be sure to check with the appropriate agency before you begin. Also, some types of older ductwork may contain asbestos; if you're unsure about your ductwork, hire a licensed professional to remove and dispose of it.
- Most areas don't require permits for installing new air conditioning systems. If you're unsure, however, check with your local government to determine the rules and regulations.
- The power of an air conditioning unit is measured in "tons," with one ton equal to 12,000 British thermal units (BTUs) per hour. The size of the air conditioner needed for any given house is based on the heat load, which is determined through a complicated formula involving the square footage, location, number of windows and doors, ceiling height and several other factors. To get a rough estimate of how many tons are required for your home, divide the square footage of living space by 500.
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