Understanding the three types of heat transfer will help you insulate smarter and not just throw money at expensive energy bills like most people. Whether you are in a hot climate or cold climate, it’s all about keeping heat in its place.
There are three types of heat transfer: conduction, convection, and radiation. All three of these should be addressed if you want an effective insulation design for your old home.
Heat is always trying to move toward cooler areas. In the winter we fight to keep the heat in, and in the summer we strive to keep it out. But it’s all the same game.
Let’s look at each type of heat transfer and how to make it work for you, not against you.
When it comes to insulating buildings, conductive heat has very little effect. An example of conductive heat would be putting a pot of water on the stove and turning the stove on high. The heat transfers directly from the stove top to the pot, and again from the pot to the water causing the water to boil.
Conductive heat transfer occurs when a cooler item comes into contact with a warmer item. The heat flows into the cooler item until a temperature equilibrium is reached. Just like electricity is conducted along electric lines, conductive heat is transferred much the same way. Break the connection and the flow stops.
How to Stop Conductive Heat: Use a thermal break where possible. Allow air space or place insulation like rigid foam between building elements to prevent thermal bridging and stop the flow of conductive heat.
Every wonder how an attic can get up to 140ºF when it’s only 95ºF outside? How about the huge temperature difference in the shade versus in the sun? Radiant heat is the answer.
Our homes are constantly bombarded by the sun’s rays, which are essentially radiant heat. Radiation keeps the earth warm during the day, and in its absence at night, things cool down quickly.
In southern climates, a huge portion of your air conditioning bill is caused by radiant heat. Regular foam or fiberglass insulation does little to stop this kind of heat transfer.
How to Stop Radiant Heat: Install a radiant barrier inside surfaces of your home that receive direct sunlight. Most radiant barriers block around 95-97% of radiant heat and cost only pennies per square foot.
This has long been an afterthought in the insulation industry and I don’t understand why. Radiant barrier can make a huge difference placed on the underside of a roof or any other exterior wall.
Think of a hairdryer, and you have a pretty good idea of what convective heat is. Convective heat affects houses by air infiltration. Hot air escaping through leaky windows, doors without weatherstripping, gaps in framing, siding, sheathing, roofing or anything really!
Old houses are big leaky sieves sometimes. That’s how they were designed. They breathe and constantly exchange air with the outside. Some air exchange is necessary for a healthy home, but you want to control when and where the air is being swapped.
How to Stop Convective Heat: Stop the airflow and you stop convection. Weatherstrip windows and doors, caulk exterior trim boards, install outlet gaskets (most switch plate covers are a big source of air infiltration and can be fixed easily with this inexpensive product), use spray foam to fill larger gaps. It’s all about tightening up the envelope.
If you design your insulation setup with this three-pronged attack, you can insulate smarter and get more bang for your buck. Find out which of these is your biggest cause of heat gain/loss and solve that problem first, then move on to the next.
When it comes to insulation, work smarter not harder.
Founder & Editor-in-Chief
I love old houses, working with my hands, and teaching others the excitment of doing it yourself! Everything is teachable if you only give it the chance.