It’s important to know up front what you’re looking to get from your heat pump. Some common reasons people switch to heat pumps are cost savings, comfort, reduced environmental impact, convenience, and aesthetics. Be sure to share your goals with your installer to ensure optimal siting and installation. It’s also helpful to discuss if the heat pump will be the only heating system, the primary system, or a supplemental system.
The primary drivers of heat pump costs are the number of indoor units installed and the complexity of the installation. Costs can be reduced by maximizing the space that each indoor unit heats and cools, as well as by selecting locations that are easy for installers to access.
Indoor unit location
- Heat rises — While an indoor unit might deliver some heat to the floor above, it won’t send any heat to the floor below. Likewise, cool air from a first floor unit in air conditioning mode will not cool floors above it. Heated air is unlikely to get past a stairwell going up and cooled air is unlikely to flow past a stairway going down.
- Consider air flow — Air flow is tough to predict and every building is different. In general, open spaces tend to be easier to heat and cool from one indoor unit, while it can be challenging for heat to go through a doorway into other rooms. A room with a door that is typically closed will not benefit from a heat pump located outside the room.
- Simplify connections — Finding creative ways to simplify installation can save money and improve aesthetics. For instance, to minimize exposed tubing and wiring (line set) without the cost of patching walls and ceilings, look for ways to locate indoor units such that line sets can be run through closets, basement/attic stairways, attached garages, basements, crawlspaces, attics, and the outside of your home. Exposed line sets should be covered with protective covers and can be painted to match the walls.
- Coordinating thermostats — The interaction among existing thermostats can be tricky. If an existing thermostat (for example, for a boiler) is in a space heated by a heat pump, then that boiler thermostat may never fall below its setpoint and may never ask for heat. As a result, other areas served by the same zone (such as bedrooms served by the boiler but not by the heat pump) may become cooler than desired. If you are not adding multiple heat pumps to cover the entire boiler zone, consider moving the boiler thermostat to another part of the boiler zone during your heat pump installation.
Indoor unit types
Here are some points to consider when picking an indoor unit:
- Wall units are by far the most popular. They are the most efficient and, because they are mounted high on a wall, they can heat or cool a large area. They are also the most conspicuous.
- Floor units are mounted on the wall down by the floor. They are less conspicuous, but are not as efficient. Their airflow can be obstructed by furniture, meaning that they may not be able to heat and cool as large a space.
- Ceiling cassettes are mounted above the ceiling and only their vents can be seen. They are typically the size of a suspended ceiling tile and they blow air in four directions from their edges. They are nearly unnoticeable, but are less efficient and may not be able to distribute warm and cool air as far as a wall unit. These are typically installed in attic floors or above suspended ceilings.
- “Mini-Ducts,” or “Compact Ducts,” have an indoor unit located above the ceiling or below the floor that is connected by short runs of ductwork to one or more registers. The main advantage is that the indoor unit is out of sight and the registers are inconspicuous. Because one indoor unit can be ducted to multiple registers they can be well suited to heating several small rooms like bathrooms and bedrooms. A common configuration is an indoor unit installed in an insulated attic connected to a grill in a hallway ceiling below. Hallway air is returned to the unit, heated or cooled, then supplied to multiple adjacent rooms via ceiling vents. Alternatively, they can be installed beneath a floor (typically in the basement ceiling below). Superinsulated homes with very small heating demands may be good candidates for a small mini-duct indoor unit with ducts throughout the house.
Ideally, ductwork should be designed by a ductwork expert, and should be as short, fat, straight, insulated, and sealed as possible. The entire system (indoor unit, ducts, and vents) should be inside the insulation shell of the home. Note that if each room doesn’t have its own “return” and “supply” vents then the distribution of conditioned air can be significantly affected by doors being open or closed. Consider that all connected spaces will get heating/cooling based on one shared thermostat.
Outdoor unit location
Ductless heat pump outdoor units can be dozens of feet away from their indoor units, so there’s a lot of flexibility as to where they are installed. Here are some considerations:
- Aesthetics — This consideration is highly personal but important. It can take a while to get used to seeing a heat pump. Careful planning can minimize the visual impact of your outdoor unit.
- Unobstructed airflow — Although it’s tempting to tuck units into tight places for aesthetic reasons, it’s important to remember that they extract heat from the outdoor air. The more access they get, the better they’ll work. Avoid shrubs, places prone to snow drifts, and structures that might block airflow.
- Door, window, and walkway interference — It’s best to avoid installing the outdoor unit where it could interfere with the operation of a door or window. In addition, outdoor units release water when they defrost in the winter, which can form icy patches. Be sure to pick a spot where that won’t be an issue.
- Roof runoff — If the outdoor unit is going to be installed under a roof drip line, then be sure the unit is equipped with a rain cap.
- Serviceability — Keep in mind ease of service when selecting an installation location
Outdoor unit considerations
- Mounting — The primary goal of a mounting system is to keep the outdoor unit above the snow.
- Foundation brackets do the best job at minimizing noise and staying out of the way of rakes, shovels, and lawn mowers.
- Ground stands minimize noise, but can be susceptible to frost heaves if installed with inadequate drainage.
- Wall mounts keep units away from rakes, shovels, and mowers, but can transmit noises inside. The noise can sound like the hum of a truck idling on the far side of the street.
- Multi-zone versus Single-zone — The primary advantage of multi-zone outdoor units is that they take up less space and are less visible because they can connect with multiple indoor units. In addition, having fewer outdoor units can reduce maintenance costs. One disadvantage is that heat (or cooling) is delivered to all the connected indoor units, even if they don’t need heat. In a well insulated house, this can overheat some rooms. Single-zone outdoor units are typically more efficient, and usually can throttle down to lower speeds without cycling on/off. Throttling down saves energy, reduces temperature cycling and can more effectively dehumidify. Having multiple single-zone units also provides backup in the case of a failure of an outdoor unit.
- Sizing — When sizing a heat pump indoor or outdoor unit, bigger is not always better. Smaller units tend to be more efficient and can often do a better job of air conditioning than oversized units.
Beyond the outdoor and indoor units, here are some other things to consider during installation:
- Line sets — Indoor units are connected to outdoor units by two insulated copper lines and one wire. It’s easiest to hide them in a closet, basement ceiling, attic floor, or on an outside wall, but sometimes they can be hidden in a wall. For outdoor line sets, matching their color to a house’s exterior and making them shorter can minimize their visibility. These decisions affect both costs and aesthetics.
- Condensate drain line — When indoor units are in air conditioning or dehumidification mode, they produce condensate, which is carried by a drain line. This water can be drained to a sump hole, sewer line, garden or gutter.
- Code Requirements — As with most residential and commercial equipment installations, it’s best to consult with your installer to ensure code compliance. These requirements may impact installation costs.