Hydronic Heating

What hydronic heating actually is

Hydronic heating moves heat with warm water instead of hot air. A heat source warms water, pumps push it through PEX tubing in the floor, and the floor becomes a gentle, low-temperature radiator that warms the bodies and objects in the room directly. Those objects re-radiate the heat to everything else, so the temperature is uniform from floor to ceiling – no hot ceiling, cold floor, or drafty corners. Because it warms you first instead of roasting the air, it needs less energy to feel comfortable. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has measured it: people stay comfortable at air temperatures roughly 2 to 4 degrees C lower with radiant than with forced air. Lower thermostat, same comfort, smaller bill. For how the heat itself behaves day to day – response, controls, the “set and forget” reality – see radiant floor heating 101, and for the forced-air comparison, radiant heat vs forced air.

What runs it? The heat-source lineup

This is hydronic’s quiet superpower: anything that can heat water can run your floor. You’re never locked into one fuel, and you can pick the source that fits your build, your budget, and your energy goals. Here’s the honest rundown of what we actually use in Ontario.

Solar deserves its own note: the low water temperature a radiant slab needs is exactly what makes solar hot water practical, and a concrete slab is the best place to store that heat. These systems are more complex and want a backup – a wood stove, a vented gas heater, electric resistance, or a heating element in the solar storage tank – but a radiant slab is one of the best ways to put solar energy to work. The full solar picture is on solar radiant floor heating and the technical solar thermal vs PV page.

Manifolds and zoning: the warm-water traffic control

If the heat source is the engine, the manifold is the traffic director. It’s the brass or stainless rail where every loop of tubing begins and ends, with valves and actuators that decide how much warm water each zone gets. Zones are areas controlled separately – a basement slab, the main floor, the bedrooms, a garage – each with its own thermostat so one part of the house isn’t roasting while another is cool. Good zoning is how comfort stays even across sunny rooms, shaded rooms, and different floors.

The catch is that zoning is great until it isn’t. Twelve tiny zones in an 1,800 sq ft bungalow cause short-cycling, balancing headaches, and parts you’ll pay to maintain. Too few zones and you get complaints. The sweet spot is zones that match how the home is actually used, set by the heat-loss design – not by how many thermostats a salesperson can sell you. The number of zones, the loop spacing, and the supply temperatures all come out of the same calculation.

Water temperature and outdoor reset: the magic ingredient

Here’s the detail that separates a system that “works” from one that’s genuinely effortless. A hydronic floor runs at a low water temperature, and the right temperature changes with the weather. The floor surface, in most cases, is dictated by the outdoor temperature: to hold a room at about 21 degrees C, the floor might sit at a neutral 22 degrees C on a mild day and a cozy 29 degrees C on a bitterly cold one. The colder it is outside, the warmer the floor – and it should never feel hot, just neutral to pleasantly warm underfoot. That’s why you can put the thick socks away in winter, but still wear shoes comfortably.

Why hydronic saves energy (three ways)

The savings over forced air come from three real mechanisms, not marketing. First, lower thermostat settings: the elevated mean radiant temperature, the lack of moving air, and heat delivered at floor level mean you’re comfortable at a lower air temperature. Second, lower water temperatures: radiant runs cooler than baseboard, which keeps a condensing boiler in its efficient range and lifts heat-pump performance. Third, no added infiltration: forced-air systems can pressurize and depressurize parts of a house and pull in cold outside air; radiant, like hydronic baseboard, doesn’t do that. Put together, a well-built radiant home is cheaper to heat than the same home on forced air. Your real number depends on your envelope and fuel, which is exactly why the heat-loss math earns its keep before you buy equipment. The dollars-and-cents are on the Ontario radiant cost page.

Quiet, clean, and out of the way

Three more things you feel every day. It’s quiet – no fan, no airflow through ducts, no gurgle of water through baseboard radiators. The only sound is the soft hum of the circulating pumps and the boiler’s power vent. The air is cleaner – there’s no forced-air stream to blow dust, pollen, and pet dander around, and no surface hot enough to scorch dust particles, which matters for anyone with allergies or chemical sensitivities. And humidification is usually unnecessary, because radiant doesn’t dry the air the way combustion and infiltration can. It’s invisible – no baseboard radiators, no floor registers – so your furniture goes wherever you want it. People genuinely find themselves lying on the floor more often; it’s that comfortable.

When hydronic makes the most sense

Modern tubing and controls have made hydronic comfort affordable and adaptable to almost any situation, but it shines brightest in a few. It’s a natural fit in well-insulated homes with standard or better windows, where the comfort payoff is high and the load is steady. It’s excellent in big open spaces with tall ceilings, where forced air struggles to keep the floor warm. It’s the practical winner in garages, shops, and high-air-turnover spaces, because the large warm slab recovers quickly after the door has been open. It’s the right call when solar is a priority, since radiant’s low water temperatures make solar hot water genuinely useful. And it’s the comfort choice for anyone with allergies or chemical sensitivities, because nothing is blowing dust around or scorching it on a hot element.

Building new? The HST rebate can cover a big slice

If your hydronic system is going into a new build, that home likely qualifies for Ontario’s enhanced HST rebate – up to $130,000 back if your build contract is signed before the deadline. Check your number before you commit.

Hydronic pairs best with ICF

An ICF home loses less heat, so the hydronic system runs at lower water temperatures - which means smaller, cheaper equipment, lower bills, and quieter operation. It's the combination we build into our own homes. See what ICF is, browse our ICF house plans (every one offered with the ICF + radiant package), run the ICF cost calculator, or check code with the OBC Code Navigator.

All radiant guides

Hydronic heating: frequently asked questions