Radiators · Baseboards · Air Handlers
Boilers Matched to Your Radiators & Air Handler
High-temperature, high-efficiency boilers for cast-iron radiators, baseboards and hydronic air handlers. Strong heat on the coldest days — and lower gas use the rest of the winter.
- TSSA-licensed gas work
- Rinnai, Navien & Viessmann
- 20+ years in the GTA
Choose your path
Which Heating System Do You Have?
Path 1
Radiators & Baseboards
Classic hot-water heat that keeps your rooms comfortable and quiet. We replace the boiler and keep the radiators you already have.
- Works with cast-iron radiators and baseboards
- Outdoor sensor for steadier, more efficient heat
- Separator to protect against old-system sludge
Path 2
Hydronic Air Handlers
Common in GTA condos, townhouses and homes. The boiler heats water for the coil, and the air handler blows warm air through your ducts.
- Low- and high-velocity air handlers
- Combi option adds on-demand hot water
- Hot enough water for strong coil output
Built for high-temp systems
Strong Heat When You Need It, Savings When You Don’t
Radiators and air handler coils need hotter water than in-floor heat. Modern condensing boilers deliver that heat on the coldest days, then turn the temperature down when it’s milder outside.
High water temperature
Combi boilers can run up to 180°F to get the most heat out of an air handler coil.
Outdoor reset
An outdoor sensor lowers the water temperature on milder days for better efficiency.
Efficient Rinnai models
High-efficiency condensing models for radiator and air handler systems.
Recommended models
Boilers We Install for Radiators & Air Handlers
Every install is sized with a heat-loss calculation — these are our most common picks.
Heat-Only Boilers
For radiators, baseboards and air handlers, paired with an indirect tank for hot water.
Rinnai I090S
90,000 BTU/h · up to 2,500 sq ft
Rinnai I150S
150,000 BTU/h · up to 3,500+ sq ft
Navien NHB-110H
110,000 BTU/h input · 102,000 BTU/h heating
Combi Boilers
Heat plus on-demand hot water from one wall-hung unit — popular with air handlers.
Rinnai IP090199C
90,000 BTU/h heat · 199,000 BTU/h hot water
Rinnai IP120199C
120,000 BTU/h heat · 199,000 BTU/h hot water
Navien NCB-240/110H
110,000 BTU/h heat · 199,000 BTU/h hot water
Done right
What We Check on Every Radiator & Air Handler Install
Heat-loss & sizing
We size the boiler to your home, not just the old nameplate.
Air handler match
We confirm the coil and blower suit your new boiler, low- or high-velocity.
System cleanliness
Older radiator systems get a dirt and magnetic separator.
Pressure & expansion
Correctly sized expansion tank and auto feeder.
Circulation
High-efficiency circulator pump and isolation valves.
Venting & gas
Safe venting route and gas line sized for the new unit.
How it works
Replacing Your Boiler in 4 Steps
Free estimate
Send photos of your boiler, radiators or air handler, or book a visit.
Right-sized quote
We recommend heat-only or combi and give you a clear price.
Clean installation
Our TSSA-licensed team installs, flushes and balances the system.
Warranty & support
One year of free labour from 4Most, plus manufacturer coverage.
Radiator & Air Handler Boiler Questions
Straight answers about boilers for radiators and air handlers.
Will a new boiler work with my old cast-iron radiators?
Yes. Modern condensing boilers work well with cast-iron radiators and baseboards. In older systems we usually add a dirt and magnetic separator to capture rust and sludge, and an outdoor sensor so the boiler adjusts its temperature to the weather.
I have a low- or high-velocity air handler. Will a combi boiler heat my place?
Yes — a combi boiler is the best fit for an air handler. The heating water stays in its own closed loop and never mixes with your hot water, and the boiler can run up to 180°F to get the most heat out of the air handler coil.
Can I keep my existing air handler?
Often, yes — if the coil and blower are in good condition and suited to your home. We check it during the estimate and tell you if anything should be replaced.
Should I choose a heat-only or a combi boiler?
If you have one to three bathrooms, a combi boiler can handle your heat and hot water in one unit. Larger homes with several bathrooms in use at once are often better served by a heat-only boiler with an indirect hot water tank.
What maintenance does a boiler need?
Very little. These units are solid and usually last 15 to 20 years, and they hardly need major service before the 15-year mark. A yearly clean and tune-up is ideal, and our maintenance plans start from $12.99. Without a plan, have a certified technician check the unit at least every 5 years.
How does the warranty work?
4Most gives you one year of free labour on any installation issue or repair. Most boiler manufacturers cover parts for 5 years and the heat exchanger, the most expensive part, for 15 years. After the first year, if you need service, you pay for the service call and the repair labour, but not for the part. We also offer extended labour warranties for 5 or 10 years.
Why isn't the installation price on the page?
Every home is different. The price depends on the boiler you choose, how it will be vented and how much piping needs to change, so we quote each home individually.
Request a Free Boiler Estimate
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