What is a whole-house HVAC load calculation?

A whole-house HVAC load calculation sums the heating and cooling loads of all conditioned rooms in a home plus infiltration and ventilation loads to determine the total BTU/hr or kW that the HVAC system must supply. This total load drives equipment selection — furnace size, air conditioner tonnage, or heat pump capacity.

How is whole-house load different from room-by-room load?

Room-by-room loads are used to size individual supply ducts and registers for duct design. The whole-house load is the sum of all room loads plus system-level components like whole-house infiltration and ventilation, and is used to select the central HVAC equipment. The whole-house load may be slightly less than the sum of peak room loads due to load diversity — not all rooms peak simultaneously.

How many BTU does a 2000 sq ft house need?

For a 2000 sq ft house in a cold Canadian climate (e.g. Toronto) with average insulation, expect 60,000–80,000 BTU/hr for heating and 24,000–36,000 BTU/hr for cooling. In a very cold climate like Edmonton, heating loads can reach 80,000–100,000 BTU/hr for the same house. Well-insulated modern homes can achieve 40,000–50,000 BTU/hr heating. Always calculate from actual building data.

What is load density and why does it matter?

Load density is the heating or cooling load per square foot (BTU/hr/ft²) or per square metre (W/m²). It is a key indicator of building energy performance. Modern Canadian building code homes achieve 20–30 BTU/hr/ft² heating. Older poorly-insulated homes may be 40–70 BTU/hr/ft². Net-zero homes can achieve 8–15 BTU/hr/ft². Lower load density means lower energy costs and a smaller, less expensive HVAC system.

🏠 Whole-House HVAC Load

Whole House Load Calculator

Aggregate room-by-room loads into a complete whole-house heating and cooling summary. Enter room loads manually or link to per-room calculations. Generates a full load report with equipment sizing, load density analysis, and PDF export for permits.

Unit System:

📄 Project Information

Project / Client Name *

City / Location *

Date

Total Conditioned Floor Area *

ft²

Number of Stories

Building Type

🌡 Design Conditions

Indoor Heating Setpoint *

°F

Outdoor Heating Design Temp * i

°F

Look up design temp →

Heating ΔT (auto)

°F

Indoor Cooling Setpoint *

°F

Outdoor Cooling Design Temp *

°F

Cooling ΔT (auto)

°F

▢ Whole-House Envelope

💡

Enter the whole-house envelope values below. These are used to calculate system-level loads (infiltration, ventilation) not captured in individual room entries. For detailed envelope analysis, use the Heat Load Calculator.

Average Wall R-Value i

hr·ft²·°F/BTU

Average Window U-Factor i

BTU/hr·ft²·°F

Ceiling R-Value

hr·ft²·°F/BTU

Window-to-Wall Ratio i

Infiltration ACH i

ACH

Mechanical Ventilation i

CFM

Calculate required OA →

HRV/ERV Efficiency i

Total Occupants

people

🏠 Room Loads

💡

Enter each room's heating and cooling load. Use the Room Load Calculator or Heating & Cooling Load Estimator to calculate per-room loads, then enter the results here. Leave loads as 0 to use the envelope-based estimate only.

Room Name Area (ft²) Heating (BTU/hr) Cooling (BTU/hr)

Rooms: 0

Room Area: 0 ft²

Heating (rooms): 0 BTU/hr

Cooling (rooms): 0 BTU/hr

📊 Whole-House Load Report — Project

BTU/hr

📈 Heating Load Density

Excellent
<15Good
15–25Average
25–40Poor
40–60Very Poor
>60

Your density: — BTU/hr·ft² — —

⚙ Equipment Sizing Recommendations

Room-by-Room Load Summary

#	Room	Area	Heating BTU/hr	Cooling BTU/hr	Heat %	Cool %

📊 Room Load Distribution

🌡 Heating Load Sources

❄ Cooling Load Sources

Export Report:

How to Calculate Whole-House HVAC Loads

Enter Project Info & Design Conditions

Start with the project name, city, and design temperatures. Use the design temperature lookup for ASHRAE 99% heating and 1% cooling temperatures for your city. The ΔT values auto-calculate.

Enter Envelope & Infiltration Data

Enter average wall R-value, window U-factor, window percentage, infiltration ACH, and mechanical ventilation rate. These are used to calculate the system-level loads beyond individual rooms. The U-value calculator helps determine effective R-values for your wall assemblies.

Add Rooms with Their Loads

Add each conditioned room with its floor area and pre-calculated heating and cooling loads. Use the Room Load Calculator for each room first, or the Heating & Cooling Load Estimator to calculate all rooms at once. You can also use the "Load Typical House" button to pre-fill a sample 2,000 ft² two-storey home.

Calculate & Review Results

Click Calculate Whole-House Load for an instant summary showing total loads, load density rating, equipment size recommendations per standard 1.4×/1.15× sizing rules, room-by-room table, and two pie charts showing heating and cooling load sources.

Export & Select Equipment

Export the complete PDF report for permit submission. Then use the recommended equipment size to select your system with the furnace sizing calculator, heat pump sizing calculator, or AC sizing calculator. Then design the duct system with the duct sizing calculator.

Whole-House HVAC Load Calculations

The whole-house HVAC load is the total rate of heat that must be added (heating) or removed (cooling) from a home to maintain design indoor temperatures. It is the sum of all room loads plus system-level loads — infiltration, mechanical ventilation, and humidification — and directly determines what size furnace, air conditioner, or heat pump to install.

Room Loads vs. Whole-House Load

Individual room loads (from the room load calculator or load estimator) are used to size supply ducts and registers. The whole-house load is the sum of all rooms plus shared system loads and is used to select the central HVAC equipment. Note that the whole-house load may be slightly less than the arithmetic sum of all peak room loads due to load diversity — not all rooms peak simultaneously.

Load Density — The Key Performance Indicator

Load density (BTU/hr per square foot) reveals how energy-efficient a building is. Modern Canadian homes built to NBC 2015+ standards achieve 20–28 BTU/hr·ft² heating. Homes from the 1980s-1990s typically fall in the 30–45 BTU/hr·ft² range. Pre-1980 homes with little insulation can exceed 60 BTU/hr·ft². Net-zero homes target below 15 BTU/hr·ft². Use the load comparison tool to see how much improvement insulation upgrades, window replacement, or air sealing could achieve.

Standard Equipment Sizing Rules

Per standard residential sizing practice, heating equipment may be sized up to 1.4× the calculated heating load to accommodate standard increments. Cooling equipment should not exceed 1.15× the sensible cooling load to prevent short-cycling. The furnace sizing calculator, heat pump sizing calculator, and AC sizing calculator each apply these rules automatically.

After Whole-House Loads — Next Steps

Select heating equipment: Furnace Sizing, Heat Pump Sizing, Boiler Output
Select cooling equipment: AC Sizing, Mini-Split Sizing
Design the duct system: Duct Sizing, CFM Calculator
Verify ventilation: Ventilation Rate Calculator
Evaluate energy savings: Payback Period Calculator
Check compliance: ASHRAE 62.1 Calculator

Frequently Asked Questions

It depends heavily on climate and insulation. For a 2000 ft² two-storey home in Toronto (cold climate, average insulation): expect approximately 60,000–80,000 BTU/hr heating and 24,000–36,000 BTU/hr cooling. In Edmonton (very cold), heating could reach 80,000–100,000 BTU/hr. In Vancouver (mild), it may only be 35,000–50,000 BTU/hr. A well-insulated 2015+ code home in Toronto might achieve 45,000–60,000 BTU/hr. Always calculate from actual building data using this tool or the Heat Load Calculator.

The furnace output BTU/hr must equal or exceed the whole-house heating load. Standard sizing practice allows up to 1.4× the load to accommodate standard equipment sizes. For a 70,000 BTU/hr heating load, a furnace with 70,000–98,000 BTU/hr output is acceptable. Note that furnace input capacity is higher than output — divide output by AFUE efficiency to get input. A 95% AFUE furnace with 80,000 BTU/hr output requires ~84,000 BTU/hr input capacity. Use the Furnace Sizing Calculator for the complete calculation.

Yes. The whole-house heating load from this calculator is the key input for heat pump sizing. For a heat pump, you must verify that the selected unit achieves rated capacity at the outdoor design temperature (heat pumps lose capacity in very cold weather). In Canadian climates below -15°C, cold-climate heat pumps (HSPF rated at -15°C or lower) are needed. The heat pump sizing calculator handles this analysis with temperature-derated capacity curves.

Oversized equipment is one of the most common problems in residential HVAC. Many contractors size by square footage rules of thumb, resulting in 1.5–2× oversized equipment. This causes short-cycling (the system runs in short bursts instead of sustained operation), poor dehumidification in summer, temperature swings, and reduced equipment life. If your calculated load is significantly lower than your installed equipment, it may be worth having a proper load calculation done and considering right-sizing at the next replacement.