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Ventilating a Radiant-Heated House: Radiant Heats but Does Not Cool, Ventilate or Dehumidify, So Here Is the HRV, the Cooling and the Design That Go With It
Heating, Cooling & Ventilation
Radiant Floors Heat the House. That Is All They Do. Here Is What Goes in Beside Them for Fresh Air, Summer Cooling and Damp July Basements
I have built radiant floor houses since the early 1990s and I would not heat one of my own any other way. Warm floors, no blowing air, no registers, quiet as a church. But a radiant floor is a heating system and only a heating system. It does not move air, so it does not ventilate. It does not cool, or not enough to count in a Georgian Bay July. It does not take a drop of water out of the air. A forced-air house gets all of that from the same blower and ducts; a radiant house has to get each piece on purpose, and the time to plan it is before the slab is poured, not the first humid August.
What a Radiant House Needs, Line by Line
| Piece | What it does | Range | Default |
|---|---|---|---|
| Hydronic radiant tubing in a new slab | Heats. That is the list. | $6 to $12 per sq ft | |
| HRV or ERV, new construction, dedicated ducts | Fresh air in, stale air out, balanced | $1,800 to $3,500 | $2,500 |
| Ductless mini-split, single zone | Cools and dehumidifies one area, heats in shoulder seasons | $3,500 to $8,000 | $5,500 |
| Multi-zone ductless, 2 to 4 heads | One outdoor unit, several rooms | $8,000 to $17,000 | $12,000 |
| Central AC with new ductwork | A small ducted air handler for cooling, the ducts do double duty for air mixing | $6,000 to $14,000 | |
| Fan coils on an air-to-water or geothermal chilled-water loop | Cooling from chilled water where the heat source can make it; a boiler cannot | quoted individually |
The radiant floor itself is priced on its own page; this page is about what goes beside it. Fan coils only make sense with a heat source that can produce chilled water, which is a question for the best heat source page.
Why Ontario prices are all over the map: the contractors and price guides we checked for this page did not agree on any line of it. The radiant floor ran $6 to $12 a square foot on our own page and $8 to $15 in a Toronto contractor’s guide. Multi-zone ductless was $6,000 to $12,000 in one national guide, $8,000 to $16,000 and up from a heat pump price guide, and $14,000 to $22,000 from a mini-split retailer for three zones. The brand, the number of heads, and whether line sets and electrical are in explain most of it. Budget $12,000 for a multi-zone system and get two or three quotes on the same written scope.
Ventilation: Dedicated Ducts, No Shortcut
In a forced-air house the HRV can ride on the furnace ducts. In a radiant house there are no furnace ducts, so the HRV gets its own: small exhaust runs from the bathrooms, laundry and kitchen area, small supply runs to every bedroom and the main living space. In new construction this is the cheapest it will ever be, $2,500 by default, because the ducts go in the open floor joists before the drywall, or in the interior walls of an ICF house where there is nothing to fight.
Put the supply grilles where they will not blow cool winter air on anyone. In a radiant house nothing else is moving the air, so a draft from a badly placed grille is the only draft in the house and everybody notices it. Whether the house wants an HRV or an ERV is on the HRV vs ERV page.
Cooling: Three Ways, and the Floor Is Not One of Them
A slab can be run with cool water in summer, and there is a page on radiant floor cooling for the houses where it works. In most Ontario houses it is a supplement at best, because a floor cooled below the dew point sweats, and a damp floor is not what anybody paid for. The cooling comes from something that moves air across a cold coil:
- Ductless heads. The usual answer on the houses we build. One head on the main floor and one upstairs covers most tight two-storeys. They also heat in October and April, when the slab is too slow to bother firing. Priced on the mini-split cost page.
- A small ducted air handler. A short duct system with a cooling coil, usually in a basement or attic mechanical space. Better for a house with many closed bedrooms, and quieter in the rooms. More money and more ducts, and it needs space you planned for.
- Fan coils. Small air handlers fed with chilled water from a heat source that can make it. Elegant, and quoted individually, because nobody publishes a tight number.
The long version of radiant against ducted air is on the radiant vs forced air page; I will not argue it again here.
Dehumidification: The Cooling Does Most of It
An air conditioner or a heat pump in cooling mode takes water out of the air as it cools; that is the drip from the condensate line. In a radiant house that is the main summer dehumidifier, and it works if the equipment is sized right. An oversized head cools the room in ten minutes and shuts off before it has wrung out any water, which is a car driven only to the end of the driveway: it never gets warm and never does the job. Most ductless heads have a dry mode for the muggy, mild days. The HRV does not dehumidify in summer; it brings in July air with July moisture, so run it low on the sticky days.
A basement in a radiant house that still smells damp in August needs a dehumidifier sized and drained properly, and I would plan for one rather than discover it. Winter dryness is the opposite problem with its own answer, on the humidity page.
A 2,000 sq ft ICF House, Priced Three Ways
The radiant floor on 2,000 sq ft at $6 to $12 is $12,000 to $24,000 on its own; that number does not change below. What changes is what goes beside it, all before HST:
Option one: HRV plus two single-zone heads. $2,500 plus 2 times $5,500, $11,000, is $13,500. Two outdoor units, but if one quits in a heat wave the other still runs.
Option two: HRV plus a three-head multi-zone. $2,500 plus $12,000 is $14,500. One outdoor unit, a head in the main bedroom too.
Option three: HRV plus a small ducted cooling system. $2,500 plus $6,000 to $14,000 is $8,500 to $16,500. Hidden equipment, a grille in every room, and it wants a mechanical space in the plan. There is no furnace blower to hang the coil on, so check that the quote includes the air handler itself.
A tight ICF house has about half the heat loss of the same house in frame, and its cooling load is small too. That makes oversizing the easy mistake. Every one of these options starts with a room-by-room CSA F280 heat loss and gain, $395 at OntarioHeatLoss.ca, or the full mechanical design and drawings at $695. My own showhome in Tiny Township is ICF on radiant floors and heats for about $100 a month in the coldest part of winter, which is what the houses at ICFhome.ca are built to do.
Questions people ask
Does a house with radiant floor heating need an HRV?
Yes. Radiant floors do not move air, and a new house needs mechanical ventilation. A radiant house needs an HRV or ERV with its own dedicated ducts, $1,800 to $3,500 in new construction, about $2,500 by default.
How do you air condition a house with radiant heat?
Usually with ductless heads, $3,500 to $8,000 each for a single zone, or a multi-zone system at $8,000 to $17,000. A small ducted air handler or fan coils on a chilled-water source are the other options. Cooling through the floor is a supplement at best in most Ontario houses.
Does radiant heat dehumidify?
No. In summer the air conditioning or heat pump does most of the dehumidifying as it cools, if it is not oversized. A damp basement may still need a properly drained dehumidifier.
Can the HRV ducts be used for cooling?
No. HRV ducts are small and carry a small amount of air; cooling needs several times as much. Keep them separate.
When should ventilation and cooling be planned in a radiant house?
At the design stage, before the slab is poured and the walls are closed. The heat loss and gain, the HRV duct routes and the cooling equipment locations all belong on the mechanical drawings.
Price the Radiant House Whole
The cost comparison calculator includes gas combi plus radiant plus ductless cooling, and air-to-water plus radiant, so the floor, the ventilation and the cooling show up in one number with a 15-year cost beside it. If you have quotes for the pieces from different trades, the $99 review reads up to three and says what fell between them.
Sources and further reading
- What is a heat or energy recovery ventilator and why do I need one?: Natural Resources Canada: HRVs and ERVs in plain language, and why an airtight house needs one.
- Heating and Cooling With a Heat Pump: Natural Resources Canada: how air-source, ductless, ground-source and air-to-water heat pumps work in a Canadian climate, sizing, backup heat and balance points.
- OntarioHeatLoss.ca services: heat loss reports, full HVAC permit packages and radiant heating design, with prices.
