How to Calculate Heat Loss in a House (Formula Explained)

A lot of heating is required to keep your house at the desired temperature.

With the energy costs increasing, you are probably concerned about rising heating bills.

Understanding heating, or more specifically, heat loss is crucial for lowering heating expenses.

Because really, if there was no heat loss, the object or body would stay at the set temperature.

The amount of heat conserved and the amount of heat lost will determine the final temperature of a body.

What is Heat Loss? 

A difference in body temperatures results in the flow of heat from one body to another.

This results in the body at a higher temperature losing heat and the body at a lower temperature gaining heat.

This happens so that both bodies achieve thermal equilibrium.

The hotter body may lose heat through one or all of the following heat transfer methods:

• Radiation.
• Convection.
• Conduction.

Why Calculate Heat Loss

As heat loss decreases the heat of the existing space, houses, and other residential buildings need to be reheated.

This loss of heat can be through the roof, walls, windows, doors, and other building surfaces.

To retain the heat for longer periods and minimize heat loss, it is important to understand the heat outlets and take measures to reduce heat loss.

Some measures you can take include installing a new furnace, storm windows, additional insulation, and more.

But before undertaking any measure, it is important to determine how much heat is being lost and from where. To do so, we perform the heat loss calculations.

Heat Loss Calculation

You must keep in mind certain factors to calculate heat loss.

First, the surface area of the body is most important, and the higher the surface area, the more heat is lost.

The second is the speed at which heat is lost. The higher the heat difference between two bodies, the faster the heat transfer.

Third, is the value of heat loss of the material.

A building may lose heat through either of the following two means:

• Conduction through the building envelopes (exterior surfaces like walls, floor, roof, windows, and so on).
• Air infiltration (replacement of the hot air from inside the house with cold air from the outside).

No material can completely insulate the heat and prevent heat loss.

Heat loss in a body cannot be stopped, but it can be minimized. Heat loss is measured in Watts.

Heat Loss Through The Building's Envelope

A building envelope is the separation of the interior and exterior of the building.

It includes the foundation, roofing system, wall assembly, doors, and glazing. It serves to protect the interior of a building.

The heat lost through the building's envelope is calculated with the formula

q=(U×A)×Δt

Where: 

• q is the total heat lost.
• U is the overall coefficient of heat transmission.
• A is the total surface area of the building.
• Δt is the difference in temperature between inside and outside temperatures.

Heat Loss Through An Assembly

As a building is constructed using different materials, the heat loss of each material is going to be different.

With different degrees of heat transfer, calculating heat loss becomes more complicated.

Heat loss of a material can be determined by its two characteristics:

• R-value: The resistance of the material to heat flow.
• U value The material's ability to transmit heat.

So, the greater the R-value, the more heat insulation, while a higher U value will result in more heat loss.

So ideally, a material must have a high R-value and a low U value.

Also, both values are reciprocals of each other so,

U value= 1/ R-value.

Because different assemblies are made of different materials, they all have different R values.

Thus, calculating heat loss requires combining the R values of all the materials to have an effective R-value for the assembly.

Next, you need to multiply the percentage of components that are made of the material.

For example, a ceiling has two columns of numbers. They are labelled “solid” and “cavity”.

These numbers represent the R-value of the solid and open cavity of the ceiling.

By adding the R values of all the solid and all the cavity portions, you can have the total R values of the solid portion and the cavity portion.

However, R values cannot be averaged. So, you need to convert them to U values. U value is a reciprocal of the R-value.

You can get the U value by 1/R. Once you have your U value, you only need to multiply the number by the percentage of the ceiling that is the cavity portion and the percentage that is the solid portion.

How Does Heat Loss Calculation Help?

Having heat loss calculations handy has several benefits.

Some of them are:

• Showing you where the heat loss is from: Knowing where the heat is being lost will help you take measures to insulate these areas. This way, you can conserve heat, experience a reduction in heat loss, and save on energy bills.
  
  
• Reducing the cost of heating: An accurate heat loss calculation will help you perfectly size your heating system. So you have a more comfortable house and cut on costs at the same time.
  
  
• When remodelling or having sections added to the house, heat loss calculations will help you calculate the additional heat you will require for the added space.
  
  
• By calculating the amount of heat being lost, you can predict future costs. This will help you budget your heating system.

Who Should Calculate Heat Loss

Heat loss calculations help determine the heating requirement of the house and ways to insulate the heat.

For more effective heat insulation, heat loss calculation must be considered right from the beginning, when the house is in planning.

Some people who can benefit from a heat loss calculation are:

• Homeowners: Heat loss calculations help owners cut their heating costs. It helps them insulate areas with more heat loss, select the perfect heating system for their home, and optimize energy conservation.
  
  
• Builders: Most governments have made it mandatory for builders to submit the heat loss calculations of their home designs. This ensures that the heating system is properly sized for the house, and the calculations help the builder build a better system that will reduce the cost of the heating system.
  
  
• Designers, architects, and energy analysts: The professionals consider heat loss calculations to make the building as energy efficient as possible.
  
  
• Heating system professionals: They calculate the heat loss of the system to design the perfect heating equipment for the space.

What Do You Need For An Accurate Heat Loss Calculation?

Whether you calculate the heat loss yourself or hire a professional for the job, you need to keep certain things in mind.

They are:

• U value: The u value is the measure of heat transmitted by a body. The u value is available for every component of the building. An inaccurate calculation of any U value will lead to wrong heat loss calculations.
• Measurements: Make sure the measurements are accurate. If the measurements are incorrect, the mere purpose of calculating heat loss is lost. With an inaccurate heat loss calculation, neither will your comfort increase nor will your heating bills reduce.
• Make sure every single heat loss area is included: When calculating heat loss, every single area that experiences heat loss should be included. We often tend to overlook ductwork and losses from air leakage.

Heat Loss Calculation Conclusion

Heating systems are expensive. And so are the monthly bills, which are on the rise with increasing energy costs.

As a result, it becomes very important to thoroughly inspect the house for the reduction of heat loss.

Heat loss calculation helps determine the areas of maximum losses so that you can conserve energy by insulating the areas.

It also helps determine a better heating system for the building, so that you get maximum heating with lesser heating costs.

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