How to Size Your Heat Pump?

• Decide if you want a heat pump mainly for cooling your house, supplementing your heat as much as for cooling, providing a significant amount of heat requirements, or as the primary source of heat for your home.
• If you had an energy advisor perform an energy audit on your home, insert your home's design heating load and cooling load.
• Otherwise, read your city's design heating temperature and design cooling temperature from the calculator input (or from the table below if you are in a large City).
• Find a period where the temperature in your city stayed close to your heating (cooling) design temperature.
• Find the portion of time during this design temperature period that your furnace/AC was working. (you might be able to get this information from your smart thermostat)
• Insert the capacity of your current heating/cooling system and these time proportions in the calculator.
• If your heating/cooling system is not providing a comfortable temperature at your home, or if your current heating/cooling systems are multistage equipment, or if you can’t find the portion of the time they were operating, you would need to model your home's envelope to find its design heating load and design cooling load.

If you take advantage of a Government benefit/incentive like the Greener Homes Grant, Canada Greener Homes Loan, and Enbridge Home Efficiency Rebate in Ontario, you are likely required to have an energy advisor perform an energy audit on your home. Your energy advisor’s report should contain a design heating load estimate and a design cooling load estimate. In deriving these estimates, the energy advisor has used both the air leakage from your home and the insulation provided by your walls, ceiling, floor, windows and doors.

If you do not have a home energy audit report handy, the second best (easy) way is to use the performance of your existing heating and cooling system. This is conditional on your current heating/cooling systems providing comfortable temperatures in your home. What we would like to know is your home's design heating load and cooling load. Natural Resources Canada considers 22 C to be the highest temperature you may need to be comfortable in your home during winter and 24 C to be the lowest temperature you need to achieve comfort at home during summer.

The heating design temperature is defined as the temperature that your environment would be at that temperature or higher for 99% of the time during the year. The cooling design temperature is defined as the temperature that your environment is at or below for 99% of the time during the year. Your heating system should provide comfort when your environment is at the design heating temperature and your cooling system should provide comfort when your environment is at the design cooling temperature. So, the design heating load is the heating capacity needed to keep your home at 22 C when your environment is at the heating design temperature (-18, -23 and -7, respectively, in Toronto, Montreal and Vancouver). Similarly, the design cooling load is the cooling capacity needed to keep your home at 24 C when your environment is at the cooling design temperature (31, 30 and 28, respectively in Toronto, Montreal and Vancouver).

Suppose you measure the portion of time your heating equipment (gas furnace, oil furnace or electric resistance heater) is working while the environment is at the design heating temperature. In that case, you can multiply that portion by the capacity of your heating equipment to arrive at the design heating load. Similarly, suppose you measure the portion of time your Air Conditioner is working when the outside temperature is at the design cooling temperature. In that case, you can multiply that portion by the cooling capacity of your air conditioner to arrive at your design cooling load.

You'll need to perform a detailed analysis that considers various factors, such as the size of your home, the insulation levels, the windows and doors, the local climate, and the internal heat gains. Manual J is an industry-standard protocol used to calculate residential heating and cooling loads. Here is a step-by-step guide:

1. Gather Information

Building Specifications:

• Floor plans with dimensions
• Window and door types and sizes
• Insulation levels in walls, roofs, and floors
• Types of building materials used

Occupancy and Usage:

• Number of occupants
• Daily usage patterns
• Internal heat gains from appliances, lighting, and occupants

Climate Data:

• Local weather data, including temperatures, humidity, and solar radiation
• Design temperature data for both winter (heating) and summer (cooling)

2. Determine Heat Loss and Heat Gain

Heat Loss Calculation (Heating Load):

• Transmission Losses: Calculate the heat loss through walls, windows, doors, roofs, and floors using the formula: Q = U × A × ΔT where Q is the heat loss, U is the thermal transmittance (U-value, inverse of the R-Value), A is the area, and ΔT is the temperature difference between inside and outside.
• Infiltration Losses: Calculate heat loss due to air infiltration. This can be estimated using air changes per hour (ACH) and the house's volume.
• Ventilation Losses: Consider heat loss due to ventilation if you have a mechanical ventilation system.

Heat Gain Calculation (Cooling Load):

• Solar Gains: Calculate the heat gain from solar radiation through windows using: Q = A × SHGC × I where SHGC is the solar heat gain coefficient and I is the solar intensity.
• Internal Gains: Calculate heat gains from occupants, lighting, and appliances.
• Transmission Gains: Consider the heat gain through walls, roofs, and windows during hot weather.
• Infiltration Gains: Calculate heat gain from warm air infiltration.

3. Use Software Tools

Several software tools can help automate and refine these calculations:

• EnergyPlus: A powerful building energy simulation program. EnergyPlus is an open source, free software available for Windows, Mac and Linux. It is produced and released by the US Department of Energy.
• RESFEN: A tool to calculate energy use for heating and cooling of residential fenestration systems.
• HAP (Hourly Analysis Program): A software for HVAC load calculations.

4. Perform the Calculation

Input all gathered data into the chosen software tool, which will process the information and provide you with the design heating load and design cooling load.

5. Analyze the Results

Review the calculated loads and adjust for any special considerations or unique aspects of your home. This step might involve fine-tuning the insulation levels, adjusting window treatments, or considering additional shading.

6. Finalize HVAC System Design

Use the calculated design heating and cooling loads to size your HVAC system appropriately. Ensure that the selected system can handle the peak loads while maintaining energy efficiency.

Example Calculation

Here's a simplified example to illustrate the process:

Assumptions:

• A room with 10m² wall area, 2m² window area, U-values of 0.3 W/m²K for walls and 1.2 W/m²K for windows.
• Indoor temperature T_inside is 20°C, and outdoor winter design temperature T_outside is -5°C.

Heat Loss through Walls:

Q_walls = U_walls x A_walls x Δ T = 0.3 x 10 x (20 - (-5)) = 0.3 x 10 x 25 = 75 W

Heat Loss through Windows:

Q_windows = U_windows x A_windows x Δ T = 1.2 x 2 x 25 = 1.2 x 2 x 25 = 60 W

Total Heat Loss:

Q_total = Q_walls+ Q_windows = 75 + 60 = 135 \, W

Repeat similar calculations for other home components (floor and ceiling), sum the results, and you will have a first approximation of your design heating load. You will need to revise this result to correct for heat loss from air leakage, passive heating of your home by the sun and the heat produced by people and appliances inside your home. Use a similar approach to calculate the cooling load.

This process ensures your heating and cooling systems are correctly sized to maintain comfort in your home year-round. We have not implemented this approach on this page because most users would not have access to the parameters needed for this calculation.

An oversized heat pump can lead to several issues, affecting both comfort and efficiency. Here are some of the key problems:

1. Short Cycling

Short cycling occurs when the heat pump turns on and off frequently because it reaches the desired temperature too quickly. This can lead to several issues:

Increased Wear and Tear: Frequent cycling can cause more wear and tear on the system components, leading to a shorter lifespan and more frequent repairs.

Reduced Efficiency: Heat pumps are most efficient when they run for longer periods. Short cycling reduces the efficiency, as the system uses more energy to start up repeatedly.

2. Inadequate Dehumidification

An oversized heat pump may not run long enough to dehumidify the air, especially in cooling mode, effectively. This can lead to:

Higher Indoor Humidity: Increased humidity levels can make the indoor environment feel warmer and more uncomfortable.

Mould Growth: Excess moisture can lead to mould and mildew growth, which can have health implications and cause damage to the home.

3. Uneven Temperature Distribution

Oversized systems can cause uneven temperature distribution within the home:

Hot and Cold Spots: The system may cool or heat certain areas quickly, leaving other areas less comfortable.

4. Higher Initial Costs

Oversized heat pumps are typically more expensive to purchase and install:

Increased Capital Costs: The initial cost for a larger unit and the installation can be significantly higher than for a properly sized system.

Higher Installation Complexity: Larger systems may require more complex installation, potentially leading to higher labour costs.

5. Noise

Larger heat pumps can be noisier:

Increased Operating Noise: The system may produce more noise during operation, which can be disruptive, especially if the unit is located near living spaces or bedrooms.

6. Environmental Impact

Oversized systems tend to be less energy-efficient, which can lead to:

Higher Energy Consumption: Increased energy use not only raises utility bills but also contributes to a larger carbon footprint.

Wasted Resources: Manufacturing and installing a larger system than necessary uses more materials and energy, contributing to environmental waste.

To avoid these problems, it's crucial to:

Proper Sizing: Conduct a proper load calculation using industry-standard methods (e.g., Manual J calculation) to determine the correct heat pump size for your home.

Consult a Professional: Work with a qualified HVAC contractor who can ensure the system is appropriately sized and installed.

Regular Maintenance: Keep the system well-maintained to operate efficiently and effectively.

An undersized heat pump can also lead to several significant problems that affect both comfort and efficiency in your home. Here are the main issues associated with an undersized heat pump:

1. Insufficient Heating and Cooling

An undersized heat pump may struggle to maintain the desired indoor temperature, especially during extreme weather conditions:

Inadequate Heating in Winter: The system may not be able to keep the home warm enough during cold weather.

Inadequate Cooling in Summer: The system may not be able to keep the home cool enough during hot weather.

2. Higher Energy Bills:

An undersized heat pump would cause your less efficient backup heating to kick in and lead to higher energy consumption and increased utility bills, despite the initial perception that a smaller unit might be more economical.

3. Reduced Comfort

A heat pump that is too small for the space it serves may result in uneven temperature distribution and discomfort:

Hot and Cold Spots: Some home areas may remain too hot or too cold because the system cannot effectively distribute conditioned air.

A heat pump is a device that transfers heat energy from one place to another, often used for heating or cooling buildings. It moves heat instead of generating it, making it an energy-efficient alternative to traditional heating systems. Here’s a breakdown of how a heat pump works:

• Heat Absorption: In heating mode, a heat pump extracts heat from the outside air, ground, or water and transfers it indoors. In cooling mode, it reverses the process, extracting heat from indoors and releasing it outside.
• Refrigerant Cycle: The heat pump uses a refrigerant that absorbs and releases heat as it circulates through the system. The refrigerant evaporates and absorbs heat in the evaporator coil and then compresses to increase its temperature.
• Heat Exchange: The heated refrigerant passes through the condenser coil, releasing the absorbed heat to the indoor air (for heating) or outdoor air (for cooling).

• Air Source Heat Pumps: Extract heat from the air. They are common and relatively easy to install.
• Ground Source (Geothermal) Heat Pumps: Extract heat from the ground. They are highly efficient but have higher installation costs due to the need for underground piping.
• Water Source Heat Pumps: Extract heat from water sources like lakes or wells. They are efficient but require access to a suitable water source.

• Energy Efficiency: Heat pumps can provide more heating or cooling output than the electrical energy they consume.
• Reduced Carbon Emissions: They can reduce greenhouse gas emissions compared to traditional heating systems that rely on fossil fuels.
• Versatility: Heat pumps can be used for both heating and cooling.
• Cost Savings: Lower operational costs over time due to higher efficiency.

• Initial Cost: Higher installation cost compared to traditional systems.
• Climate Suitability: Air-source heat pumps are less efficient in very cold climates, so it is best to use cold-climate air-source heat pumps for colder regions. Cold-climate heat pumps are specifically designed to provide higher efficiency at very low temperatures. Using ground-source heat pumps or water-source heat pumps is preferable for extremely cold climates.
• Maintenance: Regular maintenance is required to keep the system running efficiently.

Heat pumps are an environmentally friendly and cost-effective solution for temperature regulation in homes and buildings.