Heat loss is a calculation that measures the amount of heat energy that is transferred to the outside of a building through a surface or material.
Most commonly, experts focus on calculating heat loss through a wall. A heat loss calculation will typically be measured in either BTUs or kW.
The heat loss through walls calculation identifies how much energy is required to keep a room or space at a desired temperature on the coldest day.
It is essential to know what heat loss is and how to calculate it through a wall, as this will tell you what type of heating system you need to heat your room to a comfortable temperature efficiently.
How to Measure Heat Loss in a House
As mentioned, there are several steps that you, your contractor or your energy auditor need to take to calculate heat loss through your walls and ducts.
6-step method to measure heat loss in your home:
1. Identify The Design Temperature of Your Home
The design temperature differs between your preferred indoor temperature and your local area’s average coldest possible temperature.
The design temperature, a straightforward calculation, is measured as Delta T.
2. Determine The Surface Area Of The Room That You Intend To Heat
When calculating heat loss through a wall, you will want to calculate the surface area by using the total length of an exterior wall and the height of that same wall.
Eliminate the size of any windows or doors along that wall when calculating the room’s surface area.
To complete the calculation, you must configure the surface area of doors and windows separately.
3. Calculate Both The R-Value And U-Value Of Your Room
The R-value and U-value of the room help you to calculate heat loss through the wall while keeping in mind the impact that insulation has on the room.
A room with insulation in the wall will have a higher R-value than one without adequate insulation.
It would help if you first calculated your R-value, and then you can use that number to determine the U-value of the room.
4. Determine The Surface Heat Loss
The surface heat loss identifies how much heat is lost through a wall due to doors and windows along the exterior wall.
The surface heat loss can be calculated by determining the U-value of the doors and windows along that wall.
Their U-values can be part of the heat loss equation to determine your total heat loss through a wall.
5. Calculate The Amount Of Air Infiltration Heat Loss
Air infiltration heat loss is a separate figure that will identify the amount of heat that is being lost through small cracks, joints and caulk around the windows and doors on an exterior wall.
Air infiltration heat loss may seem minor and insignificant, but it can significantly impact the total heat loss in a given room.
However, air infiltration heat loss can be fluid, as a room’s wind speed and temperature changes impact it.
A specific formula can be used to determine air infiltration heat loss.
6. Use A Heat Loss Formula To Determine Total Heat Loss
Here’s the formula for calculating heat loss through a wall:
Total Heat Loss = (Surface Area) x (Delta T) x (U-Value) + (Air Infiltration Heat Loss)
Where:
Surface Area = the total surface area of the exterior walls (excluding windows and doors) in square feet
Delta T = the difference between the design temperature and the outdoor temperature in degrees Fahrenheit
U-Value = the overall heat transfer coefficient of the wall in BTU/(hr·ft²·°F)
Air Infiltration Heat Loss = the amount of heat lost due to small cracks, joints, and caulk around the windows and doors in the wall in BTU/hr
Once you have determined all of the various figures and calculations that are included as part of the heat loss equation, you can identify what the total heat loss is within your room.
