Step 25a – Heat Pump Installation

A heat pump consists of an indoor unit and an outdoor unit that are connected by a bundle of flexible piping and wiring called a lineset. The lineset provides a path for refrigerant, condensation, electrical power, and electrical communication signals to go back and forth between the two units.

The indoor unit is installed first. A metal bracket is provided for mounting the unit on the wall and a template is also provided to ensure that the hole in the wall for the lineset is cut out at the proper location. All that you need to do is mount the bracket to the wall with the screws provided and use the template to drill the proper size hole in the wall. You then hoist the indoor unit into place, threading the attached piping through the hole as you hang the unit on the mount.

The next step is to attach the lineset. I purchased a lineset that came with an electrical cable already bundled in but you can purchase it separately as well. I also purchased a drain hose for the condensation. Cold air is unable to hold as much moisture as warm air, so anytime you are cooling warm air you will create condensation. If you don’t want this moisture to drip out of the unit as it builds up, you must provide a path for it to go outside or to a drain. The drain hose was easiest to install and just screwed on to the connector attached to the indoor unit. Next, I connected the electrical wiring to the indoor unit. The wiring contains four wires, two for power (+,-), one for communication, and one for ground. You simply strip the wires and attach them under the screws, keeping in mind which color goes with which connection. The last two connections for the lineset are for the refrigerant. There is a larger flexible pipe called the suction line that carries condensed refrigerant and a smaller one, called the vapor line, that carries vaporized refrigerant. These pipes are under very high pressures so the connectors, called flare fittings, must be tightened with a torque wrench to just the right amount of tightness. I purchased a special crescent style torque wrench because the regular socket style won’t work for this application. The correct torque to use for each pipe was listed in the installation manual.

The final and most complex step is to install the outdoor unit. First, I poured a small concrete pad to ensure the unit would remain stable and level. I embedded anchor bolts in the concrete before it cured and after it was completely cured, I bolted some pressure treated wood to them. I built up a stand with more pressure treated wood and then bolted the unit onto this. The stand will ensure that winter snowfall will not damage the unit. I finished the stand off with some scrap siding to give it a nice, clean look. Next, I used a post hole digger to mount a pressure treated 2×6 into the ground next to the unit and attached an AC disconnect to it.

I had already run the wiring for the heat pump from the main panel to a junction box inside the wall under the heat pump way back when I had installed all of the wiring for the house. At this junction box, I had transitioned the wiring from indoor type wiring (NM) to outdoor rated wiring (UF) and then run the UF cable in a conduit to the outside. I had installed the conduit way back before pouring the foundation of the house. This kind of advanced planning was important because it allowed me to have fewer holes in the walls of the house and fewer pipes and wires taking up valuable space for insulation in the exterior walls of the house than the average heat pump installation does. All I had to do now was dig down to locate the conduit and pull the UF wires out and run them up the side of the 2×6 post and into the AC disconnect. Then, I ran a flexible conduit from the AC disconnect to the heat pump, and attached the wires to the appropriate screws on the outdoor unit. The unit uses 240 volts of power, so there are actually two hot wires each carrying 120 volts, instead of the usual hot and neutral wires. There was also a ground wire included. The next step was to connect the lineset to the outdoor unit. First, I ran the condensate hose to an exterior drain near the outdoor unit. I ensured that the hose was continuously sloped downward so water would not pool in a low spot before it got to the drain. Next, I connected the wiring from the lineset to the outdoor unit, ensuring the same colored wires were attached to the same numbered screws as on the indoor unit. Last, I again used my torque wrench to attach the refrigerant piping to the outdoor unit.

It was now time to “pull vacuum” on the refrigerant piping. The refrigerant has a lower freezing point than water, and operates at extremely low temperatures, so the slightest bit of moisture in the piping will form ice crystals and decrease the performance of the system. By “pulling vacuum”, I will decrease the pressure inside the piping. This will remove any moisture and/or contaminants in the system. I purchased a vacuum pump and hoses and connected them to the charging port on the outdoor unit. Next, I turned on the pump and watched as the pressure gauge slowly worked it’s way towards 29.92 inches of mercury, known as a perfect vacuum. I left the pump on for an hour to ensure that it got as close to perfect vacuum as possible, and then turned it off. I let it sit for 24 hours to ensure that there weren’t any leaks in the system, and to be safe, I used a refrigerant leak detector as well. When I felt good about the integrity of the system, I removed the caps on the refrigerant ports and used an allen wrench to release the refrigerant into the system. Once the piping was filled with refrigerant, I removed the pump hoses from the charging port and replaced all the caps I had removed.

All that was left now was to turn on the system and test out both heating and cooling operations to ensure the system was working properly. The unit comes with a remote control and it is very easy to toggle between heating and cooling modes. It was a perfect day to test both, about 65 degrees, and the system performed as advertised. There was a little room left in the conduit to run a CAT6 wire for internet and then I used spray foam to fill in any air gaps inside the conduit and to provide some insulation.