Efficient Heating with Minisplit Heat Pumps: Page 2 of 4


Inside this Article

Outdoor portion of mini-split heat pump.
Indoor portion of mini-split heat pump.
This wall-mounted indoor air handler is equipped with a pump that is used when the condensate cannot drain by gravity.
A ceiling-mounted indoor air handler can be slightly less efficient, but is less obtrusive than a wall-mounted unit.
A stand-mounted outdoor unit, raised above typical snow levels. The cap prevents snowmelt from accumulating on the coil.
A floor-mounted indoor air handler looks like a space heater, but with heat-pump efficiency.
A wall-mounted outdoor heat pump allows placement flexibility and simplifies installation. Care should be taken to avoid installing outdoor units near bedroom windows.
Air filters help improve indoor air quality. They are easy to remove and clean with soap and water or a soft vacuum brush.
Heat pump controls can be on-the-unit or wall-mounted thermostats, handheld remote controls, or smartphone apps.

Installation Considerations

The indoor unit’s style typically depends upon the wall space available, whether the installation is for a retrofit application or a new home, and your aesthetic. For example, a floor- or ceiling-mounted indoor unit might be preferred due to aesthetics, or the available width on a wall may dictate the model that will fit in that space.

Indoor units are connected to their outdoor units via electrical wiring and two insulated copper lines. The wiring provides electricity to the indoor unit from the outdoor unit and provides communication between the two units. An additional line drains condensate that is captured by the indoor unit when running in cooling or dehumidification mode and transports it to the building’s exterior.

The practical details for routing these lines may affect the style and placement of indoor unit that is used. Wall-mounted units tend to have the highest rated capacity and can be simpler to install when mounted on an exterior wall or on a wall with a closet or chase on the opposite side. These configurations allow easy access to the refrigeration fittings and often permit the lines to be surface-mounted within a chase. When refrigeration lines are concealed in building partitions, the installation process is more complex.

Floor-mounted units share a physical size similar to that of modern radiators. When installing these units, the refrigeration piping, wiring, and condensate can be routed through the wall or through the floor. In rooms with limited upper wall space or depending on your aesthetic, these models may be preferable to wall-mounted units.

If you’d prefer less-visible indoor units, ceiling cassettes and units with limited ducting may be used. One particular model of indoor unit serves as a picture frame to disguise the presence of a heat pump. Some of these units may have reduced performance, installation limitations, or may be significantly more expensive.

Most outdoor units look similar to one another, with a key difference being that outdoor units with larger capacities tend to be physically larger. When used in areas with little to no snowfall, outdoor units can be installed on a slab. In cold climates, outdoor units are typically installed on a wall bracket or a ground stand to elevate them above the snow line and to provide adequate clearance for draining during defrost mode.

When determining the location of the outdoor unit, there are a few considerations. If the unit is located under a drip edge at a roof eave, a rain cap should be installed to direct any rain or snow melt to the front of the unit. If this moisture splashes onto the back of the unit, it will likely be pulled into the heat exchanger, where it could freeze. Additionally, there needs to be sufficient airflow for the fan. If the unit is mounted with a shrub in front of it, this will decrease the output by restricting the amount of air that can be used for extracting or expelling heat. The electrical system in the outdoor unit is considered a source of combustion and must have adequate clearances from propane tanks and gas regulators.

Multizone Systems

There are several approaches to integrating a heat pump into a home. The most budget-minded solution is to install a single-zone unit in the most heavily used living space. If more conditioned zones are needed, multiple single-zone units may be used, but another option is a multizone heat pump.

Multizone MSHP systems connect a single outdoor unit to several separate indoor units. Each indoor unit has its own controls. Indoor unit styles can be mixed and matched. For example, one zone of the MSHP might utilize a wall-mounted indoor unit, while another zone could utilize a floor-mounted or ducted unit.

Using a multizone system reduces the electrical installation work compared to multiple single-zone units. The trade-off is that the cold-weather output of one multizone MSHP is typically less than that of multiple single-zone MSHPs. For example, the heat output of two Fujitsu 12,000 Btu/hour single-zone heat pumps at 5°F is 75% higher than the output a single Fujitsu 24,000 Btu/hour multi-zone heat pump with two indoor units attached.

A key characteristic of MSHPs is that as the outdoor ambient temperature drops, so does the amount of heat that the MSHP can extract from the outdoor air. The drop in efficiency varies by manufacturer and model. Multizone MSHPs often see a larger drop in efficiency when compared to comparable single-zone units.

Comments (6)

Greg Smith_0_0's picture

Mini splits are a much better option on the backup panel than a central HVAC unit. I always cringe when someone send me a load profile with a 5T AC unit, or two... You can get so much more bang for your buck from your storage system if you are smart about what loads you run when the grid goes down.

Marc Fontana's picture

Thanks for the article . A few questions : What is the average cost for a small 1-zone unit? Do they require a 240v circuit ? What maintenance is there on the outdoor unit ? Can installing a MSHP system be a DYI project ?

vwoodruff@insourcerenewables.com's picture

Marc, the average cost for the equipment for a single-zone mini-split heat pump is around $2k. The cost including labor typically is in the $2,500-4,000 range depending upon the size of the unit and the difficulty of the installation. Though there are 120V models, their performance tends to be dwarfed by the 240V models. Maintenance on the outdoor unit includes cleaning the coil periodically - annually clearing leaf debris, for instance, and a low pressure coil cleaning wash every few years. With the high performing units, it is highly recommended to have a refrigeration professional perform at least that portion of the installation. The greenhouse gas potential from losing refrigerant from these units is not to be ignored.

Ronald Gilliland's picture

Has anyone measured the power draw on their mini-split even when the unit is powered off? I have a Fujitsu Halcyon 9RLS3 and have found that there is a continuous draw of 100 watts after using the control panel to fully power the unit off. That seems a shockingly high power draw for a device intended to be highly efficient. During months when in Pennsylvania climate when there is no need to use the unit this parasitic load adds up to a large power usage. I now keep the breaker off to avoid this except for the times when need for unit is clear.

Vince Caruso's picture

Nice article. Some comments on instalation could include self install units now available, some may be moved to new home or other rooms many times as they have valves in the precharged hose's connectors. Just screw them on and turn on the valve. This could be a real cost savings for DIY'er. Great technology for solar powered homes.

Sammy Popwell's picture

there is more work involved than just screwing on the freon lines. Manufactures suggest that you use a triple nitrogen purge on initial installation.This is done by purging with nitrogen the pull a vacuum on the freon lines. Do this 3 times each time breaking the lines with nitrogen until you can reach a vacuum of at least 500 microns. this will then have any or all moister remover from the system.Moisture in a HVAC system is NOT GOOD. as far as the mini splits go, we install a lot of them and the house we are building this year off grid will have nothing but mini split heat pumps installed.

Show or Hide All Comments