Warming Up with Radiant Heat

The 3 AM tip-toed scamper to the bathroom can be avoided! Not with a prescription, but with the increased comfort of warm,radiant-heated floors. The concept of radiant heat has been around since the Ancient Romans, but allowing heat to rise naturally to create even warmth in a room is finally starting to gain in popularity for today’s homeowners. Instead of conventional heating systems where a radiator sits against a wall creating pockets of hot and cold air throughout the room, this highly energy-efficient system heats your floors, which then transfers heat evenly throughout the rest of the room.  

Comfort level is also greatly increased with radiant heat. In addition to solving the problem of cold tiles, the objects in the room (couches, chairs, etc.) will be heated via the floors, allowing the average temperature of the room to be lower while maintaining a higher level of comfort for the people in it. This allows homeowners to save big on their heating bills. Other benefits of radiant heat include the absence of both visible components and noise output from the system. There are several methods of installing radiant heat, and the method that you choose will depend heavily on the design of the house and rooms in which you want to add radiant heat. 

An inslab hydronic system is an efficient method of heating floors. Radiant systems can also be used for outdoor heating applications. (Photos courtesy Uponor)

Hydronic Radiant Heating

If you’re installing radiant heat during the construction process, the most efficient way to heat your home is through a hydronic in-slab radiant heat system. For this method, you will need to design a loop system of tubing to circulate hot water under the floors. Depending on the width of the tubing, the loops will vary in recommended length. The most commonly used tubing size is 1/2 inch, which cannot have loops longer than 300 feet. Each loop is connected securely to a manifold and when the system turns on, hot water is pumped through the tubing. The water heats the concrete slab, and the heat emanates from the floors, rising into the rest of the room. When the room reaches the temperature set by your thermostat, the hot water will stop circulating, but the slab will remain warm and keep your room at the desired temperature for several hours before requiring more hot water to circulate. 

What You Need for an In-Slab System

A Loop CAD Design. If it’s your first time dabbling in radiant heat or you just want to be sure it’s done right, you can get a loop CAD drawn by a Radiant Certified Designer, usually for under $100. This CAD (Computer Aided Design) maps out the installation of your tubing system. A loop CAD with a materials quote is $75 from PexSupply.com.

ThermaPEX Tubing. A hydronic system uses cross-linked polyethylene tubing with an oxygen barrier. It is flexible enough to bend easily and strong enough to be approved by all major plumbing and heating codes.

The manifold is the hub of a hydronic system.

Manifold. The manifold is the hub of a radiant heating system, connecting to the supply and return lines with as many ports as you have loops of tubing. If more than 12 loops are in a system, multiple manifolds may be necessary.

Circulator Pump. The system requires a quality pump, from manufacturers such as Taco or Grundfos, to circulate the water throughout the system. If there won’t be potable water involved, a cast iron pump is a cost-efficient way to get the job done.

Check Valve. This valve ensures that water can only flow one way through the system.

Mixing Valve. Boiler water cannot go directly into the hydronic radiant system, the water must be mixed with cold water, sending 180-degree F water to heat your floors.

Thermostat. The interface between you and your heating system, the thermostat will control when the heat is turned on and how long it stays on to achieve the desired temperature in the room.

In-slab radiant heat systems can also heat driveways and walkways to eliminate snow and ice accumulation.

Sensors. In-slab sensors will communicate to the thermostat the temperature of the slab, while floor sensors will communicate the surface temperature of your floors to prevent any gapping, cupping or warping due to excessive heat.

Expansion Tank. The expansion tank maintains proper pressure within the system.

Air Eliminator. This device removes all excess air from the system to ensure silence and a steady water flow during operation. 

Hydronic systems can also be installed beneath floor joists.

Joist Radiant Heating Another option is to use hydronic radiant heat using the joists in the ceiling of one room to heat the room above it. Aluminum transfer plates are screwed to the underside of the subfloor, two across for the span of each joist bay. The tubing is then run and secured in the joists along the aluminum transfer plates. Once installed, be sure to thoroughly insulate between the joists with fiberglass batts to ensure you aren’t losing heat as some radiates to the room below. Have a licensed electrician run wire from the room thermostat to the relay switch and then to the circulating pump. You’ll need the same items listed above for slab installation as well as extra insulation, aluminum transfer plates and the 3/4-inch drywall screws to secure them in place.