Radiant floor heating…It’s awesome! Does it make sense in your situation?
In the USA, the most common type of heating is a furnace, called “forced air,” that blows air around your house in metal duct work. When the house gets cold, the furnace kicks on, and you feel warm air blowing out of the vents. Then the air in the room cools down again, and the process continues. This is a sort of instant gratification. It is very American, actually.
Let me illustrate this with an analogy. Your body is 98.6 degrees, right? When you exhale, your breath is about 98 degrees or something less. If our hands are cold, we can blow air out of our mouth to warm up our hands. Do your hands stay warm after one breath of air, or do you need to keep blowing air? Imagine trying to warm up a cup of coffee with your breath. It could probably be done, but it would take a constant flow of heat from your breath to accomplish this. You will probably pass out before the coffee heats up. THE SAME THING HAPPENS WITH A FURNACE. When hot air blows out of your vents, it warms up the air, but it does not warm up the floors, the walls, the tables, the chairs, and all the other solid items in your house. Do you remember learning about conduction in science class? More heat can be stored in a solid or liquid than a gas. Air is a gas, and furnaces try to heat you (a solid) and your house (a solid) by storing heat in air that blows on you. It does not have a lasting effect, and therefor it is not efficient. (It also blows a lot of dust, mites, and other allergens around that are not good for your respiratory health).
Radiant heating works by transferring the heat from a liquid to solids. In other words, water in pipes is heated up, and those water pipes touch your floors and transfer the heat to your floors. The heat in your solid floors conducts to the other solid items in your home, and the heat is more efficiently stored. It also feels more cozy because it is a long-lasting, continuous heat that warms you to the core instead of just blowing air over your skin.
Staple-up in-floor heating pipes with metal fins to disperse heat
Notice all the STUFF in the ceiling of an existing home. This must all be removed and replaced before installing in-floor radiant heating pipes.
So how do you get radiant floors in your home? Water pipes (usually plastic called PEX) need to be attached to your floors. This is easiest to do when your house is under construction. If you are pouring concrete floors, the PEX is laid our before the concrete is poured, and they get permanently cast into the concrete. If your floors are framed with wood, the PEX is usually stapled up to the underside of the floors. This is pretty easy to do in new construction since there’s not too much stuff in the way (like lights, wires, insulation, and plumbing). In a remodeling situation, it is a bit more challenging since you first need to remove the ceiling and everything inside of it before you can staple up the PEX. You even need to grind away any nails or staples that may be poking through the floor, so they don’t accidentally puncture the PEX water pipes. This demolition work can get very expensive (likely more costly than the price of the radiant heating system itself). This gets even more challenging in a crawlspace where workers would need to work on their backs to staple PEX to the underside of a floor. Nothing is impossible, but having a clean slate helps to keep the cost feasible. New construction and new additions are pretty easy to integrate radiant floor heating.
Project foreman inspecting in-floor heating in existing slab. (Notice the wood shelves in the background… a worker set those there, and they punctured the water pipes. Extreme caution is necessary).
Water pipes laid in concrete slab before it is poured. Notice the insulation board below the pipes.
If you want to install the PEX into an existing concrete slab, you would either need to break up the slab and pour a new one, or you could cut out grooves to put the pipes into. Then you would cover those grooves with another layer of concrete and possibly another floor material. We have used radiant floor heating with success in all different floor materials - including hardwoods. Hardwoods do tend to shrink and swell with changes in temperature, so “engineered hardwoods” are a better choice when using radiant floor heating although we have never actually seen a problem with real hardwoods (only heard of them…knock on wood…literally).
There is a possibility of using electric radiant floor heating. This is not very efficient though. The cost of electricity to create the heat is not justifiable at this time. Most radiant heating is powered with natural gas or propane which is a lot cheaper than the electric counterpart. Electric radiant floor heating can be a viable option for small areas like bathrooms though. Small wires are laid on the floor (like a heated blanket), and they are covered with mortar and tile. A thermostat on the bathroom wall controls the system, and a thermostat with a timer can help keep the operation cost reasonable.
Manifold panel that sends heated water from a boiler to various parts of a home through PEX water pipes
Gas powered radiant floor systems work with a boiler. A boiler is a box about the size of a shoe box for cowboy boots, and it has a series of water pipes that pass over a flame. The flame heats the pipes, and the water in the pipes gets hot. It is pretty simple. Once the water pipes leave the boiler, they separate out (in the manifold) into different pipes for each area of your home. Each of those areas can have their own thermostat, so you could individually control the heat. These pipes travel back to the boiler to keep reheating the water in the pipes. There is a complicated panel of pipes called a manifold that needs to be located near the boiler. This is where the water pipes separate out to travel to the different areas - and later return from those areas before being sent back into the boiler for reheating. This manifold is the “brain” of the system which has sensors that link back to the thermostats in each room and also link back to the boiler to tell it when to heat up some more water.
Besides their small size and efficiency, another good part about boilers is that they can also be a substitute for your hot water tank for your shower, tub, and sinks. This saves even more space. The boiler and manifold just need to be located in an area where you can run a vent pipe to the outside (since burning flames indoors requires oxygen to burn and also requires exhausting of the gasses to the outdoors).
If you are considering adding in-floor heating in an addition, you must also consider what you will do with your existing heating system. It is my opinion that two separate systems is too complicated. Also, once you have the boiler and manifold panel, it is a shame to not use that infrastructure to its maximum potential to heat the whole house - instead of just the new part of the house. You could remove the existing heating system and expand the in-floor heating to the existing house, or you could consider not doing radiant and just extend your current system to the new addition. Sometimes your existing heating system is not big enough to heat up additional square footage though. Your builder and architect can help you evaluate that. Sometimes we advise people to just make their current system work 150% to heat the addition and existing spaces until it breaks. Then they replace the existing system when/if that happens.
In summary, it is easy to incorporate in-floor heating in new construction and additions, but retrofitting it into an existing condition must be a labor of love since paying someone to do it for you would be a major expense.
If you’d like to learn more about our design process, visit www.josharch.com/process, and if you’d like to get us started on your project with a feasibility report, please visit www.josharch.com/help