Radiant Heat: When to Consider

Retrofitting radiant heat adds comfort to your home while it lowers energy bills, and installing it is easier than you think.

Water is recirculated through tubing hidden in a conductive panel under your finished floors. Image: Warmboard

When it comes to keeping warm, it’s hard to beat radiant heat for comfort and efficiency. Hot water running through tubes beneath the floors heats your house evenly without the dryness or expense of forced air, both of which can make your hair stand on end all winter. Radiant heat is quiet, draft-free, and doesn’t circulate dust or allergens around the house.

At $5 to $15 per square foot, radiant systems are generally two to three times more expensive than forced air to install, but they can be up to 40% more energy efficient, meaning you’ll start recouping those costs right away. Because the tubes go under flooring or behind walls, it’s easiest to install radiant systems during new construction. But there are some situations where retrofitting radiant is worth considering.

If you want to add warmth to a first floor

Love your farmhouse’s old wood floors but hate breakfasting in your down coat? Adding radiant tubes on the underside of the first floor can make your kitchen as cozy as a bread oven without disturbing a single plank.

From an unfinished basement, installers can snake the radiant tubes between the joists, connect them to a manifold linked to your boiler, and add a water pump, thermostat, and insulation. “The best way to do it is to use aluminum heat-transfer plates that we screw under the floor, then snap our tubes into it,” says Gary Hayden, owner of Premier Comfort Systems in Norfolk, Virginia, and the chairman of a committee on radiant-heating development with the American Society of Heating, Refrigerating, and Air-Conditioning Engineers.

The plates conduct the heat up through the flooring above. Radiant can be used with most flooring materials, though your installer should set the temperature controls to prevent overheating that could warp wood. If you’ve got carpeting above, avoid heat-trapping sponge pads.

If you want to turn your bathroom into a spa

A bathroom’s small size makes it perfect for modular radiant panels that go directly under the tile. These half-inch plywood panels, made by manufacturers such as Uponor and Viega, come pre-grooved to hold 5/16-inch plastic tubes. You remove existing flooring, attach the panels and tubing, connect to the boiler, and lay new tile. The panels raise the height of the finished floor slightly, so you may have to adjust doors or add a new threshold to ease the transition.

Because you pay the same amount for the boiler and system controls regardless of square footage, it can get expensive to install hydronic radiant heat in just one room. Another option for a bathroom is electric radiant heat—cables integrated into a roll-down mat, made by companies such as SunTouch, or thin cables that can be laid directly in a layer of lightweight concrete under the finished flooring.

“When the project does not have a boiler, or you don’t want the expense of piping to your boiler, it’s a nice option,” says Gary Hayden. Electric costs less to install—$400 to $700 for an average-size bath, according to manufacturer WarmlyYours—but is more expensive to operate, which makes it a particularly good choice in a guest bath that doesn’t get frequent use.

If you’re building an addition

During a remodeling job, when you’re already pulling up floors or building new rooms, is a perfect time to consider upgrading to radiant. Installers can lay the tubing right into your new concrete slab, a method that is generally about a third less expensive than retrofitting heat panels or between-the-joist tubing.

If you want to cozy up your basement

You bought that expensive 72-inch plasma TV, but the clammy underground air makes your basement media room seem like an afterthought. Radiant gets rid of that dank feeling.

Heat panels can be laid over the existing concrete floor, or, if you’re pouring a new slab, a network of tubing can be embedded directly in it. Remember that panels will add to the finished height, which could be a problem if you’ve got low ceilings and a tall family. You may also need to change the tread height of the bottom step, and possibly the entire staircase, to comply with some local building codes.

Or you could apply panels just to the walls. “This is a great choice if you don’t want to raise the floor,” says Jim Prisby, a technical services representative for Uponor. It has some design benefits, too. “You can build up the panels to chair-rail height,” Prisby says, “and then you have a nice place to put pictures.”