How Does Heat Travel In A House?

You likely haven't thought much about how heat travels since middle school science class. While this topic probably isn't at the forefront of your mind, it impacts your life daily. How heat travels influences your energy bills, energy usage, and how comfortable you are in your home.

South Central Services insulates homes and commercial properties with spray foam insulation. We've insulated hundreds of projects, and each revolves around how heat travels and how we can stop it. Your home is no different.

This article will give you a crash course in heat transfer. Specifically, by the end, you will know:

• The three types of heat transfer
• How the weather affects heat transfer
• Key areas that need insulation
• The role of ventilation in preventing heat loss

The Science Of Heat Transfer

Heat transfer in a home occurs through three primary methods: conduction, convection, and radiation. Each method plays a distinct role in how your home heats up and cools down. Conduction, convection, and radiation affect everything from the temperature of your floors to the sun's warmth through your window.

Conduction

Conduction is the process of heat moving through materials. If you place a metal pot on a hot stovetop, the pot will begin to heat. Because the metal has direct contact with the burner, it conducts heat. We traditionally think of this heat transfer method when discussing insulation.

In a house, conduction occurs when heat moves through walls, ceilings, and floors.

Materials like metal and wood are both conductors of heat. Insulation's role is to provide a barrier that heat finds challenging to pass through.

The effectiveness of insulation is measured in R-value—the higher the R-value, the better the insulation's ability to resist conductive heat flow. Insulation is commonly made of paper, glass, and plastic, all materials with poor conductivity.

Convection

Convection is the concept of heat being carried by moving air. If we return to our stovetop example, you may think of a convection oven. These ovens are designed to cook more evenly because heat circulates through the air.

You may also remember this idea from middle school science: hot air rises, and cool air sinks. Heat naturally moves through the air. Heat is also drawn to the cold.

Heat always travels from hot to cold, even in the air.

Any opening in a home will invite air to exchange. In the summer, hot air will welcome itself inside and send your conditioned air outside. In the winter, the air you pay to heat will slip out into the cold, leaving you with cold outside air instead. Stopping convection heat transfer requires an airtight seal.

Traditional insulations do not combat heat transfer through convection. Fiberglass batts and loose fill insulations allow air to pass through them. These budget insulation products do not create an airtight seal. Spray foam insulation is one of the only insulations that can effectively fight conductive and convective heat loss.

Radiation

Radiation is the transfer of heat in the form of electromagnetic waves. Unlike convection, which occurs with airflow, radiation does not need a medium. The sun's warmth on your skin is a classic example of radiation.

In your home, radiation can cause heat to transfer from warm areas to cooler ones, even without direct contact.

Radiation is why you can feel the heat from a hot oven even when standing several feet away.

Insulation can reduce heat transfer by means of radiation. More often, you will hear about the part of energy-efficient windows in stopping radiant heat transfer. However, insulation can also create a barrier to radiant heat transfer. For example, if your attic has warmed up all day and becomes hotter than the rest of the house, that heat will radiate down through the ceiling. With insulation on your attic floor, radiant heat transfer is slowed.

Heat Transfer In Different Seasons

As important as the methods of heat transfer are, it is vital to understand how heat transfer changes depending on the season. Because heat moves to the cold, air moves throughout your house differently in different weather.

Managing Heat In Winter

In winter, the goal is to keep heat inside. However, the heat wants to escape. Any gap or crack in your home will lead to uncontrolled air exchange.

Most of your home’s heat is lost through your attic, which you can think of as the “lid” of your house. As the air in your house warms up, it convects upward. Hot air rises and cold air sinks. This warmer air finds its way out of your home through any air leaks in the ceiling.

This exchange of air is often referred to as the Stack Effect. As the warmer air leaves through the “lid” of your house, new air must replace it. Without new air, your home environment would be in a vacuum state. The replacement air is often sucked into the home from the bottom. Basements, crawl spaces, and band boards are all examples.

This air exchange leads to unstable temperatures in the home and high energy bills. An airtight seal in your attic can prevent heat from either entering the attic at all or escaping from the attic.

Managing Heat In Summer

In summer, you want to keep the heat out. Again, your attic insulation is key to managing your indoor climate. A poorly insulated attic can experience convection and radiant heat, reaching temperatures as high as 150 degrees Fahrenheit.

Without appropriate attic insulation, that heat can radiate through the ceiling into the rest of the home. The different temperatures throughout the house must be addressed with more HVAC power, raising your energy bills.

Areas That Need An Airtight Seal

Climate and season impact how heat travels, but neither change what areas of a home need to be insulated. There are four key areas of a home that benefit from insulation year-round.

1. Attics And Roofs

Heat rises, and in homes with poorly insulated attics or roofs, this can lead to significant energy loss. Warm air that has risen to the attic can escape, pulling cold air into the living spaces below. Upgrading attic insulation can prevent heat from escaping.

Depending on how you use your attic space, you can insulate your attic floor or the underside of your roof. You won't need to insulate both, but one of those surfaces should have an airtight seal.

2. Exterior Walls

Walls with inadequate insulation allow heat to conduct through easily, leading to a loss of warmth in winter and a gain of heat in summer. Even with adequate amounts of budget insulation, heat can still travel through the air without an airtight seal.

Exterior walls comprise a considerable portion of the building envelope. The building envelope needs the best insulation to stop air infiltration and heat transfer.

3. Basements And Crawl Spaces

These areas are often ignored but can be significant sources of cold drafts and moisture, which can also affect your home's overall temperature and comfort. A poorly insulated basement or crawl space is often responsible for drafts, cold floors, and even musty air.

Insulating basements and encapsulating crawl spaces can help maintain a consistent temperature throughout the home, prevent pipes from freezing, and reduce the chances of moisture-related issues like mold.

4. Doors, Windows, And Other Openings

Even small gaps in door and window framing can enable a lot of air transfer. It's vital to check for gaps where utilities enter the home, as these can be points for unwanted air exchange. Properly sealing these gaps can significantly reduce heat loss. Air-sealing products like can foam and silicone caulking are useful for these smaller gaps.

The Role Of Mechanical Ventilation

We've addressed how heat transfers and why it matters for your insulation. At this point, you may be wondering how air can travel in your home. If insulation creates an airtight seal to prevent convective heat transfer, how will you get fresh air inside your house?

An airtight seal doesn't stop air from ventilating; it only stops uncontrolled ventilation and the heat transfer associated with it. Air still needs to ventilate and circulate through your home, which is where mechanical ventilation comes into play.

Mechanical ventilation systems ensure that air moves efficiently throughout the house. Automated HVAC systems use fans to circulate air, essential for comfort and air quality.

In modern homes, heat recovery ventilators (HRVs) and energy recovery ventilators (ERVs) can help maintain a comfortable climate without losing heat. Depending on the season, these HVAC units transfer heat between outgoing stale air and incoming fresh air.

The Bottom Line About Heat Travel In Your Home

Understanding how heat travels in your house and taking steps to manage it effectively can profoundly impact your comfort, energy consumption, and wallet. Every home improvement should help to control heat transfer.

With a robust understanding of convection, conduction, and radiation, homeowners can prioritize air sealing. As a result, you will enjoy a more comfortable living environment and save on energy costs.

Now that you understand how heat travels in your home, you need to decide which energy-efficiency upgrade is best for you.

• Learn about crawl space encapsulation
• Discover the benefits of insulating your attic with spray foam

No idea where to start in your home? Learn about home energy audits, which can create a personalized blueprint for energy-efficiency upgrades.