Hot water or hot air: choosing a main heat source
A boiler heats water and sends it through pipes to radiators or floor loops, while a furnace heats air and blows it through ducts. Neither is better everywhere; the right choice depends on the house layout, how you want it to feel and whether you plan to add cooling or ventilation.
What is the basic difference?
A furnace is a forced-air system. Air from the house passes over a hot heat exchanger and a blower pushes it back out through ductwork and registers. A boiler is a hydronic system. It heats water, and a pump circulates that water through baseboards, radiators or tubing in the floor.
Both commonly burn natural gas in Canada, although either can be electric, and a heat pump can supply hot water for hydronic heating or warm air for ducts. So the real choice is the delivery method, not just the fuel.
How do they feel and perform?
Water carries far more heat than the same volume of air, so hydronic systems move heat quietly through small pipes. Rooms warm evenly, there is no fan noise from the heating itself and no blast of moving air. Radiant floors are the extreme case, covered in the radiant floor heating guide.
Forced air has its own strengths. It responds fast, filters air through a media filter, and the same ducts can carry air conditioning and fresh-air ventilation. Ducts can also be noisy and unbalanced if poorly designed, and a short cycling furnace in a mild fall can produce temperature swings.
Humidity is a practical point on the prairies. Winter air is dry, and humidifiers tie in easily to a ducted system. Hydronic homes usually need a separate solution.
What about cost and efficiency?
Equipment costs vary by region and year, and installation dominates. A boiler with a pipe network costs more to install in a house that has only ducts, since you are adding piping to every room. In new construction the gap narrows depending on design. Retrofitting ducts into a house built for radiators is equally disruptive.
On efficiency, condensing boilers and condensing furnaces both reach roughly the mid-nineties percent in rated efficiency when conditions allow. A condensing boiler only reaches that level if the return water is cool enough, which favours low supply temperatures. That is the thread running through the guide on low temperature hydronic heating.
Lifespan also differs, and boilers often last longer than furnaces with maintenance. See typical lifespans.
What did a district loop do differently?
The Drake Landing neighbourhood in Okotoks used neither a boiler nor a furnace as its main source. A central energy centre circulated warm water through a district heating loop, typically at 40 to 50 degrees Celsius, to small air handlers in each of its 52 homes. In effect it combined the two ideas: water as the transport, warm air as the delivery. The heat itself came from solar collectors and underground storage, and later monitoring reported 97 percent solar share by 2012 and 100 percent in the 2015-16 heating season.
From around 2020 the system developed deterioration and maintenance problems, decommissioning began in 2024, and most homes switched to natural-gas furnaces. The tradeoffs are a useful reminder that central systems need an owner and a maintenance plan for decades.
For a typical house, the practical advice is to match the choice to what the building already has, unless a bigger renovation is planned. A heating contractor can size either system from a heat-loss calculation.
How should you decide?
Work through the questions in order. What does the house already have? Swapping like for like is cheapest, and ducts or pipes already in the walls are a major sunk cost. Do you want cooling? If so, ducts become more attractive. Are you planning a major renovation, such as opening floors or walls? That is the time to consider hydronic floors. And what heat source do you want in ten years? A boiler loop can be driven by a heat pump later, while a ducted house can switch to an air-source or ground-source heat pump with the same ducts. The comparison is in air source vs ground source.
Ask a contractor for a room-by-room heat-loss calculation, not a rule of thumb. It takes an hour or two and avoids oversizing, whichever system you choose. The furnace replacement cost guide lists what a good quote contains.
Quick answers
Is a boiler more efficient than a furnace?
Rated efficiencies are similar for modern condensing units. Real-world efficiency depends on sizing, controls and, for boilers, how low the return water temperature is.
Can a boiler provide air conditioning?
Not by itself. Cooling needs ducts or separate ductless units, which is one reason forced air is common when cooling matters.
Can I switch from a furnace to a boiler?
It is possible but expensive, because pipes and emitters must be added to every room. It usually makes sense only during a major renovation.