This Is How Your Insulation Work In Summer & Winter

Most of us know that you can have a moderate temperature in your house throughout the year with an HVAC system. However, professional heat and temperature experts tell us that good insulation is just as important as the HVAC system itself. Unfortunately, the insulation aspect is often neglected when homeowners, and even some builders, install HVAC systems in a new or renovated house.

The reason might be that we understand the logic of why and how an HVAC system with its components such as a thermostat, air-conditioning unit, furnace, and attic fan, works, but think of insulation only as “something on the ceiling and in some walls to keep out the heat or cold.”  The question is: How does insulation work and how can your house benefit from insulation?

Simply put, insulation material on ceilings, floors, windows and walls is meant to block heat from entering the home in the summer and to hold heat inside the house during the winter. As a result, an insulated house is cooler than the outside temperature in the summer and warmer than the outside temperature in winter. 

In this article, we’ll explain what are the principles involved in insulation, look at the type of material that can be used, and how insulation material should be installed to be effective. In other words, we’ll discuss how insulation works.

Scientific principles

To begin to understand how insulation works, you’ll first have to know something about a few basic scientific aspects or mechanisms that are normally associated with the insulation process.  


“Convection” refers to the way heat circulates through liquids and gases, including air. This circulation is according to the basic scientific rule that lighter, warmer air will always rise, and cooler, denser air will always sink.

That is one of the reasons why the rooms on the upper floors of an uninsulated house normally feel warmer than the rooms on the ground floor. The warm air rises to the highest places. 

The temperature of this circulating air is sometimes called “ambient temperature” as it reflects the temperature of the air in the environment. This is the temperature we normally refer to when, for instance, we indicate the temperature is 70 degrees Fahrenheit, and it is the temperature generally controlled by the HVAC thermostat.  


“Conduction” has to do with the way how heat moves through materials.  When the flow of heat is not blocked in a specific type of material, that material is a good conductor of heat. Stainless steel, for instance, is a good heat conductor. You can test this by leaving a stainless steel spoon standing in a pot with boiling water.  After a while, you will not be able to touch the spoon’s handle without burning your hand. The heat from the boiling water has been easily and swiftly transferred to the handle as the steel is a good heat conductor. 

A wooden spoon, on the other hand, is an example of a weak heat conductor. You can leave it in a pot with boiling water but you’ll always be able to touch the handle of the spoon. 

When insulating a house, materials that are weak heat conductors form the basis of the process. 

Radiant heat

Radiant heat travels in a straight line and heats anything solid that absorbs its energy. The important special characteristic of radiant heat is that it is independent of air temperature. It is a heat gain you can feel while the ambient temperature can be quite the opposite.  

To understand this concept, think of the heat you gain from a campfire while you are sitting on the snow around the fire. You’re gaining heat, while the ambient temperature stays low. It is the same principle when you stand outside in the sun on a cold winter’s day. You gain heat from the sun while the ambient temperature is low.   

There can also be a loss of radiant heat.  When you open your freezer’s door on a hot summer day you experience a heat loss to the interior of the freezer. 

The gain and loss of radiant heat can also be incorporated into the home-insulation process. 

Two home insulation methods and how they work

There are two distinctively different ways to insulate your home. Nowadays, however, both ways are often used together when installing insulation material in your home.

Use low conductive material to keep hot air in or out

Using low conductive material to keep hot air either outside or inside your home is the original way to insulate a house and is still the basis of most insulation processes. It works according to the principle that low conductive insulation materials slow the flow of heat.  

Use reflecting insulation to reduce the radiant gain

With reflecting insulation you use reflecting materials to reduce radiant heat gain or loss. Sun can for instance be partly blocked by using reflecting material on a window. 

Why effective insulation is necessary

In winter

Heat always flows from warmer to cooler areas and only stops flowing when there is no longer a temperature difference in the areas. In practice, it means that if your house is not insulated heat generated in the house will in winter flow quickly from all heated living spaces to unheated places like attics, basements, and garages. And the heat will easily “escape” to the cold outdoors. 

Heat can also move through interior floors, ceilings, and walls, to equalize the temperature in all spaces.

The only way to keep the warm air confined to a specific space or room is to thoroughly insulate the room.  The “work” of the insulation during winter is to keep heat in the house.

In summer

During summer, warmer outside air will flow into your house trying to equalize the interior temperature with the heated outside temperature if your house is not insulated.

The only way to keep the warm air out of your house is again with thorough insulation. 

The “work” of the insulation during summer is to keep the outside heat out of the house.

The insulation-HVAC work relationship

HVAC systems are designed to maintain the comfortable temperature you want to have in your house. You program the HVAC thermostat in such a way that the heat lost in the winter must be replaced by your heating system and the heat gained in the summer is removed by the HVAC cooling system. 

Proper insulation in your home will decrease this heat flow by providing an effective resistance to the flow of heat.

Material to use to resist conductive heat flow

There are various materials to be used as insulation material. The “R-values” are used to indicate the insulation effectiveness of the material. 

R-Values in traditional insulation material

The R-value is the way to indicate the material’s resistance to conductive heat flow. The higher the R-value, the more effective is the material to be used as insulation material.

What determine the R-value?

To determine the R-value the type of insulation, the material’s thickness, and its density have to be taken into consideration. The R-value also depends on temperature, aging, and the accumulation of moisture. 

Can you increase the R-value?

You can increase the R-value of the insulation in your home and enhance the resistance to heat flow by installing more layers of insulation. The thickness of the insulation material will theoretically help to increases the R-value and the resistance to heat flow, but when the density of the material is affected by the extra layers’ compression the R-value can actually decrease. 

It is recommended that you contact your local insulation contractor to help you choose the right insulation material.

Radaint barriers – reflective materials

Nowadays, radiant barriers are also widely used to help with the insulation of a home. Where traditional insulation materials’ effectiveness is found in their ability to absorb heat and thus slow down the flow of heat (the R-value), radiant barriers are highly reflective materials whose “work” is to re-emit radiant heat rather than absorb it. Therefore, radiant barriers have no inherent R-value. Their effectiveness lies in their ability to reduce heat gain by reflecting heat away from the living space.

Effectiveness of insulation

Depending on how and where the insulation material is installed, the effects can differ. This happens because heat flows more readily through some building materials than through others, and this process is known as thermal bridging. Insulation filling cavities also reduces airflow.

For the best results, you should insulate the whole house – from the roof to the ground or cellar if there is a cellar in your house.

Let’s list and discuss places you must remember to insulate for effective blocking of heat. 


To seal the attic space when the attic is not completed to be used as a “room,” insulate it from the rest of the house by inserting insulation material between and over the floor joists. Remember to insulate the attic access door as well. 

If your attic is being used with or without dormers, you have to insulate between the vertical wall separating the unused attic space on one side and the conditioned space on the other side. (Commonly known as “knee walls.”) Put insulation material also between the studs of the exterior walls and the roof, and the ceilings.

Loose-fill insulation is typically installed in an attic and normally guarantees that the attic insulation works. Loose-fill insulation is less expensive than other materials and provides excellent insulation if installed correctly.

If you live in a region where very high temperatures can be expected, it is recommended that you consider it to install a radiant barrier in your attic rafters as well. This will reduce summer heat gain. 


Insulate all walls between living spaces and unheated spaces such as garages and storage areas. And don’t forget about the foundation walls above ground level and in basements.

If you live in a very cold climate it is always good to insulate all your exterior walls. This is more expensive and is usually not a DIY job, but it may be worth the cost of a contractor and insulation material. And remember that if you have to replace the exterior siding on your home, consider adding insulation at the same time.

If you’ve decided to insulate your existing exterior walls, a good choice will be to use blow-in insulation. It can be applied added to exterior walls without much disturbance in your house. 

Cathedral Ceilings 

As both sloping sides of a cathedral ceiling are parallel to the pitch of the roof, it offers an ideal “gateway” for the flow of heat if the space between the roof deck and the ceiling is not adequately should unlike a vaulted ceiling, which does not follow the shape of the roof. The roof cavity must be totally air sealed from the conditioned space.


To make insulation more effective, it is recommended that you also apply insulation to floors above unconditioned spaces. Heat can flow through the floors from heated areas to unheated areas. 

Windows and doors

To further restrict the flow of heat ensure to seal around all windows and doors. This will help a lot to keep outside heat outside your home in summer, and inside your home in winter.

There are many videos available with tips on how to insulate your home yourself.


We hope that this article has changed your conception of home insulation. You should regard insulation as a tool helping you to keep your house at a comfortable temperature throughout the year, and not only as some “inactive material covering your home’s ceiling and walls”   

It may sound strange, but insulation material is “working” in your house 24/7. Its work is to slow heat movement between building materials. It uses dead air space to trap air and slow heat flow between objects and places with different temperatures. In the winter it keeps warm air in your house, and in summer it prevents hot air from outside to enter your home. 

Proper insulation saves you energy as your air conditioning and heating appliances don’t have to work so hard to keep your house at the desired temperature. And by saving energy, you save money on your utility bill.

Charles John

Experienced HVAC technician with 8 years of experience in the industry. Capable of handling all sorts of heating and cooling equipment as well as proficient in operational management, construction-related techniques such as preventative maintenance, electrical troubleshooting and AutoCAD

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