Key Takeaways
- Load Calculation First: Never size equipment based on existing system – perform proper heat loss/gain calculations to avoid costly oversizing mistakes
- Control Strategy Critical: Ensure thermostat compatibility and sufficient control wires for heat pump, auxiliary heat, and emergency heat functions
- Airflow Assessment: Check Total External Static Pressure (TESP) before installation to identify and correct duct restrictions that could cripple system performance
- Protection Essential: Install surge protection and voltage monitoring for inverter systems to prevent expensive solid-state component failures
The Push For Electrification
No matter your political stance on climate change, let’s put that aside for a moment: there’s a major push for electrification on a global scale.
Simply put, the term electrification is the removal of appliances, vehicles, and HVAC equipment that contribute to our carbon footprint.
For example, removing a natural gas-fired furnace and replacing it with a heat pump, or replacing a gasoline-fueled vehicle with an electric one.
There are legitimate concerns that a quick and rapid push for electrification may not be wise, as the current electrical supply grids may have difficulty keeping up with the charging of EVs and running heat pumps as the primary heat source.
The argument for a slow and observant approach to electrification is a good one. As with any new concept, there are learning curves, and we don’t want to be left out in the cold—pun intended!
I’m going to tackle this article from an HVAC technician and HVAC business owner’s perspective to discuss some factors that should be considered before installing a heat pump and also during the installation process itself.
On-Site Assessment
The first step in this process is not to quote the job or pick equipment.
It’s to understand if any grants are in place locally to help the customer save money.
We’ll also need to understand the process of how and when the grant money is allocated.
Some customers will have already done their homework and be well-versed in the grant procedure if one exists in your area.
An initial on-site assessment will be required to understand your customer’s needs.
Inspecting the existing equipment and recording all info is recommended as it will help us get an idea or baseline of equipment size, but don’t use the existing equipment to size the current job—this is extremely important.
Control System Requirements
Take note of the thermostat and how many conductors are within the thermostat cable.
Ensure the thermostat can control a heat pump and auxiliary or emergency heat. Understanding heat pump reversing valve operation is crucial for proper control setup, as the O/B terminal configuration varies between manufacturers.
Also, ensure there are enough conductors to control the new system.
We may need to suggest a new thermostat if the current one cannot control a heat pump, and it’s possible we will need to run additional control wires from the thermostat’s location to the indoor and/or outdoor unit.
Air Distribution Analysis
Check the current system TESP (total external static pressure).
Checking this will give you an indication of any duct restrictions on the supply or return side.
Knowing this will allow the contractor to correct any duct design issues before the new installation.
If the TESP is high, there are a few things that could cause this, such as an undersized duct, blocked or closed supply or return grills, existing equipment being oversized, or the air filter being too restrictive.
I always recommend 4″ or 5″ filters, which offer more filtration surface area and less system pressure drop.
Electrical Requirements
Inspect the electrical panel and ensure there is space for any upgrades that may be required.
We will discuss this later, but some heat pump installs use resistive electric heat as auxiliary or emergency heat.
If so, there is a chance the panel in the home will need an upgrade of some sort.
The customer may want to bring in their own electrician, or they may ask you to bring in yours.
Either way, you’ll want to have all the info and be in clear and constant communication with the electrician during any electrical upgrade or installation.
Outdoor Unit Location
Where will the outdoor unit be mounted?
A useful advantage of some heat pump outdoor units is that they are of slim design, similar to ductless outdoor units; this can help with some installations.
You can mount them on a stand or wall bracket. It really depends on a few things.
I wouldn’t recommend using a wall mount on buildings where the bracket must lag to structural studs; this can cause vibration issues that the occupants may not enjoy. In this case, it’s best to use a stand.
If you’re in a cold climate and snow is a factor, ensure to keep the outdoor unit high enough where accumulating snow will not affect performance.
Load Calculation
One last task on the initial assessment is to record any info needed for a block load calculation.
A perimeter measurement, number of windows and doors, sizes, type, and age.
Height of home (to calculate stack effect), age of home, amount of exposed basement wall to the outside and if known, insulation value, etc.
Please speak to a local HVAC designer, and they will be able to help. For more accurate sizing methods, consider using real-world gas consumption data rather than relying solely on traditional calculation methods.
✅ Note: Depending on time and budget, a full room-to-room load calculation can be performed. If the project is new construction, the designer should be able to work off a set of drawings.
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Post Assessment
After the assessment, a designer should perform a load calculation, or in-house, if you have a program that allows this.
A blower door test can be utilized to capture proper infiltration rates.
If a blower door test is not done, the designer will make an educated guess based on the information you have submitted to them on the home’s infiltration rate.
If there are major ductwork concerns after your assessment, you can also utilize the help of a designer to rectify these issues at a design level.
Once the heat loss and heat gain have been determined, equipment can be selected appropriately for the application. Understanding heat load factors can provide a quick 10-second calculation method for verifying proper sizing.
There are many options out there and many brands.
Inverter technology has enabled heat pumps to become very efficient, and cold weather heat pumps have changed the game for cold weather climates with systems that can heat down from -4 to -22°F (-20 to -30°C).
Inverter systems also have the advantage of performing over a wide capacity range.
In cold weather climates or places that can experience cold snaps, auxiliary heat should be implemented.
Auxiliary heat can be added using in-duct electric resistive heat or a dual fuel setup that can include a natural gas or propane furnace.
In this scenario, the heat pump would be the primary heat source, and the auxiliary heat source would be utilized in extreme weather conditions or when the heat pump cannot provide sufficient heat to the space.
A proper control setup is key to preventing any interruptions in comfort.
Some systems will require a proprietary control system, and some will allow you to select your own 24-volt thermostat.
Important Sizing Consideration
I want to emphasize this note as it is super important.
If a home has a heat loss of 60k BTU and a heat gain of 24k BTU, how do we size?
Let’s keep in mind that a heat pump will need 400 cfm to 450 cfm per ton to run effectively.
If we size the heat pump to the heating load, we need 2000 cfm to 2250 cfm.
In most retrofit applications, as it pertains to this example, we’ll find ductwork that is only designed to carry 800 to 1200 cfm.
The solution here is to size closer to the cooling load but as close to the heating load as possible.
For example, if the ductwork allows, select a 3-ton heat pump and add in auxiliary heat to supplement the heat pump with resistive heat or, in the case of dual fuel, a complete backup source of heat that will switch over as the heat pump capacity falls off.
Installation
As with any system, please read the installation manual prior to installation.
A centralized heat pump install is quite similar to a central air conditioning install.
Follow proper piping practices: ream, deburr, and clean pipe, braze with nitrogen, and ensure flares are made at
