A central hydronic system is one type of radiant-heating system. A hydronic heating system includes a heat source (a boiler or a heat pump), a pump, a manifold, and a distribution loop that carries hot fluid throughout the home and back to the heat source. Hydronic systems generally cost more than forced-air systems, but they’re low maintenance; they lose less heat via distribution tubing than ducted systems do via ducts; and they don’t take up a lot of space.

Baseboard hydronic radiators were once common, but today tubing under or in the floor is generally used to deliver the hot fluid. This keeps the residents’ feet warm and gently induces air movement. As the air in a room cools, it falls until it reaches the floor, where it’s warmed, and then rises toward the ceiling. A similar effect occurs with baseboard hydronic radiators.

Getting It Hot

The boiler that heats the circulating fluid can be fired by gas, propane, or oil; by a heat pump; via solar preheating; or by (highly energy-inefficient) electric resistance. The pump forces hot fluid from the boiler to a manifold, which separates the delivery system into zones. Each zone is controlled by its own thermostat, making it possible to fine-tune heat delivery to the zones for comfort and energy savings.

Gas, propane, or oil boilers require an exhaust flue, and should be provided with combustion air ducted directly from the outdoors; aim for a sealed-combustion unit. Ask your contractor for a high-efficiency boiler. As with a furnace, it is a thermal advantage to place the boiler within the house’s heated space, but codes sometimes prohibit this.

Tubing

Radiant-floor heating uses cross-linked polyethylene (PEX) tubing to circulate the heated fluid, turning the whole floor into a radiator. The tubing can be within a concrete slab or beneath a wood floor. Because a concrete slab has thermal mass, the heat from the tubes lingers longer, but the concrete also takes longer to heat up. Tubes within concrete are extremely expensive to repair, unlike tubes beneath wood floors. Wood flooring, however, slows the heating response, and repairs to wood floors can damage the tubes if the workers don’t know the tubes are there.

Some flooring materials aren’t warrantied over radiant-heating systems. Heated floors must be especially well insulated from below and along any edges exposed to the outdoors.

Baseboard Radiators

If wall-to-wall carpeting is a must, consider hydronic baseboard radiators rather than tubes in the floor. These will affect furniture arrangements (if you block a radiator, you won’t feel the heat) and will need periodic cleaning. In the case of remodeling, installing baseboard radiators is far less complicated than replacing an entire floor.

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