» How To Install Central Air | Air Conditioning

Our home is a two story garrison (big box) with a finished basement. There are 3 bedrooms and a bath upstairs; a fairly open lower level with the living room, dining room, kitchen and laundry; and a family room, office, storage, and mechanical room in the basement. The heating system is forced hot water through baseboard radiators so the first task was to plan the duct system I would need to install.

Using Microsoft Visio, I mapped out my home and a couple alternatives for the duct work and location of the air handler.

Option 1: Air handler in the basement.
Placing the air handler in the basement would enable a simpler duct system reducing labor, time, and cost. However, the return air supply would come exclusively from the basement. I hypothesized that the upstairs would not be cooled enough because the hot air would not be able to be sucked down to the basement to be circulated through the system. Furthermore, since the return air inlet is on the bottom of the air handler, I would need to devise a method to raise the unit off the floor (also needed for condensate drainage) and allow the installation of an air filter.

Option 2: Air handler in the attic.
With the air handler in the attic (in a horizontal orientation) return air could come from the ceilings of the top and middle floors - thus the system would be cooling the hottest air. However, the duct system would be significantly more complicated and expensive. Furthermore, there would be some energy loss due to the heat in the attic.

After going back and forth and consulting with my brother, I went with Option 1. The hypothesis turned out to be false and the whole house is cooled just fine. Enough mixing of the air on the top floor occurs to provide an even distribution of cool air that is circulated throughout the system. Furthermore, if the air conditioner reduces the temperature by a certain amount, it is better to start with the cooler air in the basement than the hotter air upstairs.

Before the system was installed, the hot and humid days would produce a temperature difference from top floor to basement of about 15°F. Now, on similar days it is closer to 5°F. It works really well.

The location of the condenser is not ideal as it receives a lot of direct sun throughout the hottest part of the day. However, it is the only location available with appropriate proximity to the electrical supply and the air handler. This is one of the reasons I opted for a higher efficiency model (12 SEER, 10 is the lowest, 18 is the highest).

Using the duct system plan above and the technical specification (page 11) from Alpine Home Air’s website, I calculated the total CFM of air that would (could) be output from the system. I did this by determining the size of duct I was using and summing the possible CFM of air that duct could provide. With this total CFM of the system, I cross referenced the specification sheet (Blower Performance and Performance Rating charts) for the air handler to determine the size of air handler required. With about 900 CFM of demand, I would need a 2.5 ton air conditioning system.

Based on the plan made above, I created a shopping list with all of the items I would need. I hit Home Depot and quickly realized a lot of re-design would be required. Most of the ductwork I hoped to find was not available and much of the different components were not compatible (a 10×4 register does not fit a 10×3.5 register boot, for example). So, re-design and improvise were constantly on my mind (my wife claims I was quite grouchy during this project, but really my mind was rather pre-occupied in thought and re-thought).

Good planning and preparation are the key to a large project such as this. Unfortunately, there are many unknowns and items that are left to be determined until you get to that point. Nevertheless, I think I could have reduced my 17 trips to Home Depot significantly with a more complete plan at the outset.

I also ended up purchasing extra tools that were not needed. The contractor said he prefers to bend the line set rather than solder joints which could be a potential leak. Had I known this ahead of time I would not have purchased the pipe cutter and plumbing kit (I left the soldering to the contractor anyway).

I purchased the equipment online from Alpine Home Air which turned out to be a great deal. They have a useful website (including instructional videos), great customer service, and very prompt delivery - right to my door. They boast on their website that the equipment has free shipping. What they really mean is that the shipping is included in the price. Plus, since it sounds so nice, they also tack on a hefty surcharge on top of that. Fortunately, they offer a 110% price match guarantee. I searched the web and found the same equipment for about $300 less (when shipping is taken into consideration). I choose to go with Alpine Home Air (with the price match) rather than the cheaper site because of their customer service and the other products I needed to order - it is easier to have a single order and delivery.

$1400 was spent at Alpine Home Air and about $900 at Home Depot.

The first, and most formidable, order of business is to install the duct work. Without a doubt, this was the most challenging aspect of the project. Not only from a design point of view, but also trying to fit the design into the existing structure of my home.

Duct Work | Top Floor

Knowing the top floor would have the registers connected to the main duct with 6" flexible ducts, that sounded like an easy place to start. To do so, I measured the location in each room where the register should be located (with reference to a known item, such as the light fixture). I then went up in the attic, carefully removed the insulation (be sure to wear gloves and a dust mask), and marked a 10"x6" rectangle near a ceiling joist. I then used a rotary tool (such as a Dremel) to cut through the sheet rock of the top floor’s ceiling. I enlisted the help of my wife to hold a garbage can to the ceiling below to catch the dust and cutout. I then placed the 10×6 insulated register boot in the hole and secured the register from the room below.

Duct Work | Bathrooms

The bathrooms are to be fed with a 4" flexible duct connected to the main duct. It branches in the attic above the top-floor bathroom closet. One branch descends through the back of the closet to the lower-level bathroom while the other provides cool air to the top-floor bathroom.

It turns out that 4" flexible ducts are probably too small for this task. It would have been better to use 6" flexible ducts to the point of the branch and then use 4" downstream from there. When the system is running, very little air can be felt coming through the diffusers. Nevertheless, the rooms are very small as well and the bathrooms are adequately cooled.

The first task was to verify that the top-floor closet was physically over the lower-level bathroom. Measuring from the opposite wall, I determined that the front of the top-floor bathroom closet overlapped the lower-level bathroom by about 8 inches. That was enough. I would run the duct from the attic through the ceiling, down the back of the closet, across the floor, and then down through the floor to the lower-level bathroom ceiling.

Next, I removed a tile in the closet and cut a hole through the sub-floor. I have learned that the best way to cut a hole in areas where the jigsaw does not fit is to drill holes every 1/2", or so. Then, use a chisel or a hand saw to cut through the remainder. It is not a clean hole, but it works.

Let me backup a bit: removing tile is not an easy task. Using a hammer and an old screwdriver, I chipped away at the mortar around the tile I wanted to remove until I could get under the tile to pry it up. Once I can pry up an edge and break off a portion of the tile, the remainder would come a little easier as I could get directly under the tile.

Once the tile is removed and the hole cut in the floor, I went downstairs to cut a corresponding hole in the ceiling - carefully measured. From the attic, I cut the two holes in the ceiling of the top-floor bathroom: one in the closet and one near the center of the room.

I then simply extended the 4" flexible duct through the hole in the closet down through the hole in the floor and to the hole in the ceiling on the lower level. The last part was a bit tricky as I had little space to work. Furthermore, I had to extend the duct down through the hole in the ceiling, connect the air diffuser, and then push it all back up through the hole.

Rather than using a register boot and a register in the bathrooms, I opted for a 4" round diffuser. This turned out to be a good choice as it would have been impossible to properly install and connect a register boot in the space between the floor and ceiling (Not to mention the fact that the 4" register boots available at Home Depot were not compatible with the registers.)

Duct Work | Ceiling to Floor | Holes

Bringing the supply duct from the basement to the attic required going through two floors and the top floor ceiling. Cutting the holes proceeded from bottom to top - with some minor changes in the design with each step. The problem was determining where the duct would go with respect to the floor/ceiling joists and what size of duct would work.

Cutting the hole in the basement ceiling revealed a floor joist a few inches from the wall and another one 16 inches on center (14.5 inch space between the joists).

Moving to the first floor I needed to remove two and a half tiles from the floor. As mentioned above, this is not an easy task. The amount of tile removed was about 3 inches larger than the planned hole to allow space for the 2×3 framing that will eventually hide the duct.

The floor joists between the first and second floors were in about the same location as the lower floor. This hole was easier to manage as there was no tile to worry about. However, the ceiling joists above the second floor were not aligned with the others. In fact, a ceiling joist would go right through the planned location of the duct. The only way around this obstacle was to cut out a section of the ceiling joist and replace it with some blocking.

Duct Work | Ceiling to Floor | Duct

The first thing to do when installing a duct stack is to assemble two half-rect ducts into a full rectangle. They snap together easily and I sealed the seams with the foil duct tape.

The duct from the basement through the first floor was 14×8 inches. They come in 4 foot sections, so I would need two ducts (4 half-rects). The bottom of the first duct runs into an obstacle: a heating pipe runs through it. I cut out a notch in either side to slip over the insulated pipe. The duct was inserted in the hole in the first floor and slid down to rest over the pipe.

The second duct would reach from the top of the first one to about 6 inches below the ceiling of the first floor. I secured it to the first duct with sheet metal screws and sealed the joint with foil duct tape.

Be careful when selecting the sheet metal screws. One type is total garbage and the other works wonders. Too bad I discovered this too late. The screws on the left are labeled "self drilling" - I suppose because the tip looks like a drill bit - but they are crap. The sharp-pointed screws on the right work very well.

I planned to put a register at the top of the duct so I wanted to reduce the duct from 14×8 inches to 12×8 inches. First, I assembled a 12×8 duct and inserted it through the hole in the second floor to meet the top of the second duct. The right sides of the two ducts aligned and there was a 2 inch gap on the left. I cut the top of the 14 inch duct down about 4 inches to create a flap that could be folded over to meet the 12 inch duct. I secured everything with screws and sealed the joint with foil duct tape.

The second section of 12×8 inch duct was installed simply on the first section on the second floor. It extended up to about 2 feet below the second floor ceiling. The final section of 12×8 inch duct would be inserted down from the attic. However, since it would also be used to connect the flexible duct from the ceiling registers, collars needed to be installed first.

First, 4 6 inch holes were cut in the duct. Then, the collars are inserted in the holes, secured with screws, and sealed with foil duct tape.

The duct assembly was then lowered from the attic, attached to the other 12×8 duct section. screwed and sealed. At this point, the flexible ducts could be attached to the collars. To do so, I slid a clamp over the flexible duct, pulled the duct over the collar, and tightened the clamp. Make sure the clamp is completely over the collar.

Duct Work | Office

Installing the duct from the plenum (see below) to the office was actually the last duct to be installed. The plenum needed to be in place first. To accomplish this step, I simply assembled three 5 foot sections of 10×4 rectangular ducts. It turned out to be about 10 inches too short, so I fashioned a make-shift register boot from sheet metal to connect the duct through the office wall and to the register.

Duct Work | Living / Family Rooms

The registers in the family room (basement) and living room (first floor) are supplied with an 8 inch flexible duct from the plenum. The flexible duct is attached to a collar at the plenum and then to an 8 inch ‘T’ section.

The branch from the ‘T’ section is then connected to a 6 inch reducer which connects to the 12×4 register boot. A damper was also installed in the reducer to control the airflow between the two rooms.

The other end of the ‘T’ section continues to another 6" reducer installed just before a 12×6 register boot that supplies cool air through the living room floor.

The 8 inch flexible duct was attached to the collar, ‘T’ section, and reducers with 34 inch plastic ‘zip-ties’. 8 inch clamps were not available.

Duct Work | Plenum

The single most challenging aspect of the entire project was to design, build and install the plenum which would connect the top of the air handler with the 3 main outlets: the 8 inch flexible duct, the 10×4 duct to the office, and the 14×8 vertical duct to the top floors. This job took an entire day.

The first task was to carefully measure the location of the 14×8 vertical duct relative to the top of the air handler. Second, I sketched a couple views of the assembly.

Third, I unfolded the assembly in my mind and transferred the sketch to sheet metal - with extremely careful measurements. Shown below is only a portion.

Fourth, I cut the pieces out and folded them back up. The easiest method I found to cut the sheet metal was to dab a small amount of oil onto the sheet metal with a brush or paper towel and cut it with a jigsaw. To fold it, I clamped a straight edge along the fold, bent the sheet metal with my hands, and then used a hammer to sharpen the corner. Be extremely careful - sheet metal cut by any means can be quite sharp.

Finally, the various pieces were ready to be assembled in place. It was a perfect fit.

The equipment is heavy. Use a hand truck to move them around and certainly seek help when lifting, etc.

Air Handler

The air handler is installed directly on top of the return air box. I first placed the return air box such that the front face would be flush the back surface of the wall and a convenient distance from the concrete wall.

You have two options for the condensate drain. Either use gravity to run the tube to a drain or sump pump or install a condensate pump. A condensate pump is like a mini sump pump which collects the water and pumps it to either outside or to an available drain when it is full. Since I had a sump pump nearby, I opted to simply run the drain tube there.

As shown above, a simple P-trap is needed to create a positive liquid seal that prevents air being sucked through the tube and inhibiting water from draining. The contractor later inserted some of the copper tubing to prevent the kink circled above.

The tube slopes gradually on its way to the sump pump.

Compressor

The compressor needs to be at least 10 inches from buildings and heavy shrubs. It should also be at least 3 feet away from the natural gas meter.

The compressor needs a solid, level base. After clearing out a significant portion of the lilacs, I leveled the ground and used 75 pounds of crushed stone as a base. The 30×30 inch plastic base was placed on the stone and checked for level.

Then, it is simply a matter of placing the compressor on the pad. The electrical access panel is on the opposite corner. The next section explains the electrical connections.

Using a hole saw, I cut holes in the wall from the outside. I cut one small hole for the electrical and one larger for the refrigeration tubes. It is also possible to cut a single larger hole through which everything is inserted. I opted for two smaller holes with the idea that it would be easier to seal with caulk later.

Be sure to turn off the main power before doing any work in the electrical panel. Seek professional help if you do not feel comfortable working with electricity or if local building codes require it.

New Electrical Sub Panel

The compressor and the air handler both require a 220 volt power supply. Each 220 volt circuit requires a double-pole circuit breaker. The existing electrical panel only space for one more single-pole circuit breaker. So, a new sub panel was required.

I wanted to supply 100 amps to the sub panel so a 100 amp double-pole circuit breaker would need to be installed in the main panel. Furthermore, one of the existing single-pole circuit breakers would need to be moved to the new sub panel to make room for the 100 amp circuit breaker.

6 gauge four wire is required to provide power to the sub panel. It is a beast to work with. The black and red-striped wires connect to the circuit breaker. The ground and white-striped wires both connect to the neutral bar.

In the new sub panel, the black and red-striped wires connect to the hot bars, the white-striped wire to the neutral bar, and the ground is connected to a lug screwed to the box. All connections made with the 6 gauge wire are corrosion-protected with Noalox - a greasy substance. This is required because the wire is aluminium.

In the sub panel, the single-pole circuit breaker from the main panel is installed first. The air handler requires a 15 amp circuit breaker and the compressor a 20 amp circuit breaker. (This is based on manufacturer’s specifications - check your documentation.) 10 gauge 3 wire (2 hots and a neutral) is used on the 220 volt circuits. The white and black wires are connected to the double-pole circuit breakers and the ground is connected to the neutral bar.

Air Handler

Connecting the power supply to the air handler is simply a matter of connecting the 10 gauge wires from the sub panel to the appropriate wires in the air handler - according to the manufacturer’s instructions.

Click to enlarge

Compressor

To provide power to the compressor, first locate the electrical disconnect in a convenient location outside near the compressor. The disconnect is a box that can be used to easily disconnect the power to the compressor.

A whip is used to connect the disconnect with the compressor and another connects the disconnect with a junction box inside. A whip is simply 8 or 10 gauge wire protected in a weather-proof sheath.

Thermostat

My home has three zones for heating (one for each floor) and therefore, a thermostat on each floor. I decided to use the thermostat on the first floor to control the cooling. The existing thermostat had support for both heating and cooling, but it would need to be re-wired. Furthermore, the current wire running into the thermostat did not have enough wires to support the cooling - it has two and three additional wires are needed. Therefore, I would need to run wires from the thermostat on the first floor, down through the wall, through the floor, and to the electrical connections of the air handler.

To accomplish this:

1. Remove the thermostat and the baseboard below the thermostat.

2. Cut a small hole in the sheetrock in a location directly below the thermostat which could be covered when the baseboard is replaced.

3. Feed the wires through the existing hole behind the thermostat, down to the new hole just created.

4. Using a long (at least 12 inches) 3/8 drill bit, I drilled a hole from the hole in the sheet rock, down through the bottom 2×4 of the wall, through the sub-floor, and possibly through a floor joist. This hole was drilled down at an angle pointing towards the final destination: the mechanical room that houses the air handler.

5. The hole drilled above was about 5 feet away from the mechanical room. Fortunately, I had access to the small space between the ceiling of the basement and the floor joists (about 1.5 inches occupied by firing strips). I fed the wire through the hole as much as possible and then fished it out from below with a wire hanger fashioned into a hook.

Once the wire was in place, the connections were made as follows:

The thermostat wire had two wires in it. Therefore, I added two wires: one of which I used both wires (labeled ‘double’) and the other I only used the white (labeled ’single’). See the imageabove for the thermostat connections in the air handler. This is a sample schematic of the connections I made.

New Outlet

During the inspection, I was told that a GFCI-protected outlet is required to be within 20 feet of the compressor. The inspector mentioned that there is a disconnect available that has an outlet built in. Rather than bother with searching and replacing such a device, I opted to simply install a separate outlet.

Using the current single-pole circuit breaker in the sub panel (which actually supplies power to other exterior outlets), I connected another 12 gauge wire and ran it outside near the compressor. I installed an exterior junction box, the GFCI outlet, and the weather protecting cover.

The finish work is performed after the inspection. It involves insulation and encasing the ducts in a wall.

I had two inspections: electrical and mechanical. The electrical only inspected the circuit breakers to make sure they were sized correctly. The mechanical took a look around, inspected the condenser and disconnect and informed me of the required outlet. They both were here for a very short time.

Insulation

Any exposed duct in a non-treated space needs to be insulated. Otherwise, a lot of water will condense on it and possibly cause water damage.

For the air duct in the attic, I decided to use spray foam insulation. It required 4 cans.

The plenum duct in the basement was insulated with a roll of 1/2 inch duct insulation and sealed with foil duct tape.

The vertical ducts on the first and second floor were insulated with normal 3.5 inch wall insulation.

Wall Construction

There are three walls that I needed to construct:

1. In the basement to cover the air handler and provide a hole for the return air.

2. On the first floor to cover the vertical duct to the second floor and provide a hole for a register.

3. On the second floor to cover the vertical duct to the attic.

In the basement, the wall was simple to frame in place around the plenum.

The other two walls required careful alignment to insure they were square and plumb.

After the framing was complete, the walls were encased in sheet rock and a corner bead was installed on the corners. The least fun part of the job was next: taping and mudding. Finally, the sheet rock was painted with a primer.

Conclusion

And that, is all! We really enjoy the cool air and it makes a big difference. It was a big project, but it was well worth the time and effort of doing it myself to save the thousands of dollars it would otherwise have cost.

Would I have done anything different if I had it to do again?

• I think a larger air handler (3 ton rather than 2.5 ton) would have been a good idea.
• I would not have reduced the vertical duct from 14×8 to 12×8 on the first floor. This causes way too much air to come through the register there and not enough to be distributed upstairs. Furthermore, we are planning an addition and may need to branch another flexible duct in the attic.

Resources:

You may also be interested in these online resources:

• Ductwork Installation