You’re not imagining it if your house feels dry every winter, with dry skin, nosebleeds, static shocks, and cracked wood floors. Forced-air heating and Ontario’s cold, dry air remove moisture from your home, frequently bringing humidity levels below 20%. The good news? Even if a humidifier wasn’t installed when your system was initially installed, you can still add one to an existing furnace. Every year, Heat Flow HVAC retrofits whole-house humidifiers into hundreds of GTA residences, ranging from new construction in Oakville and Burlington to older bungalows in Hamilton.
We will cover each and every little thing that you need to know about installing or even upgrading a humidifier to your existing furnace: how it functions, which types are suited best for your home setup, brand compatibility, installation challenges, and whether your heat pump configuration makes a difference. We’ll also go over the warning indications, safe practices used by HVAC contractors like us, and the reasons this idea is among the most economical comfort enhancements.
Is It Possible to Install a Humidifier in an Existing Furnace?
Yes, even if it wasn’t installed at the time, almost all of Ontario’s forced-air furnace systems are capable of supporting a whole-house humidifier. A whole-house humidifier upgrade integrates directly with your furnace blower and ductwork to provide uniform humidity to every room your HVAC system serves, compared to portable units that only treat a single space.
The primary requirement is having a central forced-air system (gas, oil, or electric furnace) with accessible ductwork near the furnace. While we’ll discuss those exceptions later, traditional whole-house humidifiers cannot be used in homes with baseboard heating or ductless heat pumps.
How Does a Whole-House Humidifier Work With Your Furnace
Instead of producing heat, a whole-house humidifier adds moisture by using the blower fan and existing airflow in your furnace. This is the process that is followed internally to allow the humidifier to function along with a furnace:
- Air travels through the return duct when your furnace is operating.
- The humidifier turns on and draws water from your home’s cold water line when the humidity is low.
- In bypass or fan-powered models, the water passes over an evaporative pad; in steam models, it vaporizes.
- After passing over the damp surface, the furnace’s dry air absorbs humidity and disperses it via your supply ducts.
- Any extra water can be safely drained to a condensate pump or floor drain.
The humidifier is automatic and energy-efficient because it is connected to your blower and only operates when your system is operating.
Types of Whole-House Humidifiers You Can Add to Your Furnace
Humidifiers are not all made equal. The efficiency of your furnace, the amount of space you have, the availability of water, and the size of your house all influence the type you choose. For homes in Ontario, the three primary types compare as follows:
Bypass Humidifiers: The Most Common Retrofit Choice
For many high-efficiency models and mid-efficiency (80% AFUE) furnaces, bypass humidifiers are the preferred option. A portion of the warm supply air is “bypassed” through the humidifier pad, where it absorbs moisture before being redirected to the main airflow, using a tiny duct that they mount on the return duct.
Pros: Benefits include low energy and water consumption, stability, quiet operation, and ease of servicing.
Cons: Requires an electrical connection for the fan, uses slightly more water.
Ideal for: The majority of residences with conventional forced-air systems in Hamilton, Burlington, and Mississauga.
Fan-Powered Humidifiers: Better for High-Efficiency Furnaces
Without the use of a bypass duct, fan-powered units draw air through the humidifier pad using an integrated fan. As long as the blower is running, they mount directly on the supply plenum and turn on regardless of furnace runtime.
Pros: Higher moisture output, faster response, works well with variable-speed furnaces.
Cons: Slightly higher water use; requires an electrical connection for the fan.
Ideal for: Newer GTA subdivisions or more recent high-efficiency Lennox, Keeprite, or Carrier systems in Oakville.
Steam Humidifiers: Overkill for Most Residential Homes
Steam humidifiers boil water to create vapor, which is then injected into the airflow. They’re highly effective but expensive to install and operate.
Pros: Highest output, no dependency on furnace heat, works with any ducted system.
Cons: High energy use (requires 240V circuit), costly installation, overkill for homes under 3,000 sq ft.
Best reserved for large custom homes or commercial spaces, not typical for most Ontario residential retrofits.
Step-by-Step: How Professionals Add a Humidifier to Your Existing Furnace
While DIY videos exist, adding a humidifier involves plumbing, electrical, and ductwork modifications that require licensed expertise, especially in Ontario, where gas and electrical codes are strict. Here’s how our technicians at Heat Flow HVAC do it correctly and safely:
1. System Assessment and Compatibility Check
We start by inspecting your furnace type (80% vs 95% AFUE), brand, duct layout, and available space near the unit. We also check for a nearby cold water line and floor drain, critical for proper operation.
2. Selecting the Right Humidifier Model
Based on your home size, furnace specs, and water hardness (common in Hamilton), we recommend the best fit. We carry and install top brands like AprilAire, Honeywell, and GeneralAire, all available for immediate installation in your home.
3. Mounting and Duct Integration
For bypass models, we cut precise openings in both the supply and return ducts and install a bypass tube. For fan-powered units, we mount directly to the supply plenum. All cuts are sealed to prevent air leaks.
4. Plumbing and Drainage Setup
We tap into a cold water line using a push-fit or saddle valve (never reducing main line pressure) and run a ¼-inch supply tube to the humidifier. A drain line with a P-trap is installed to prevent sewer gases from entering your home, a common oversight in amateur installs.
5. Wiring and Control Calibration
The unit is wired to your furnace’s 24V control board or a dedicated humidistat. We never use line voltage. Then we calibrate the humidistat based on outdoor temperature, critical in Ontario winters to avoid window condensation.
6. Testing and Safety Verification
We run the furnace, verify water flow, check for leaks, confirm drainage, and measure output with a hygrometer. Only when everything operates safely and efficiently do we sign off.
Is Your Furnace Brand Compatible?
Good news: nearly all major furnace brands used in Ontario support humidifier retrofits. Here’s what we see most often:
- Lennox: All Elite and Merit series work well with AprilAire 700 (fan-powered) or 600 (bypass).
- Keeprite: Common in older GTA homes; bypass humidifiers integrate easily with proper plenum clearance.
- Carrier / Bryant: High-efficiency models benefit from fan-powered units due to lower airflow temps.
- Goodman: Standard plenum design makes retrofit straightforward.
- Trane: Requires careful duct tapping; we recommend fan-powered for variable-speed models.
If your furnace is over 15 years old, we’ll assess whether adding a humidifier makes sense, or if a furnace upgrade with built-in humidifier prep is smarter long-term. Learn more about warning signs your furnace may need repair or replacement.
Which Humidifier Type Works With Your Furnace?
Not every humidifier suits every furnace. Choosing the wrong type leads to poor performance or installation delays. Here’s how they match up:
Furnace Type | Best Humidifier Type | Why It Works | Installation Notes |
|---|---|---|---|
| Mid-Efficiency (80% AFUE) (e.g., older Lennox, Keeprite) | Bypass Humidifier (e.g., AprilAire 600) | Uses warm supply air to evaporate moisture; low water/energy use | Requires duct tapping on both supply and return; needs 12+ inches of clearance |
| High-Efficiency (90%+ AFUE) (e.g., Carrier, Trane, new Keeprite) | Fan-Powered Humidifier (e.g., AprilAire 700, Honeywell HE360A) | Built-in fan ensures consistent output even with cooler airflow | Mounts on supply plenum only; requires 24V power tap from furnace board |
| Ducted Heat Pump Air Handler | Fan-Powered or Bypass | Blower runs long enough to distribute moisture; no combustion heat needed | Must verify blower runtime settings; some models need humidistat upgrade |
| Older Furnace (15+ years) with limited space | Compact Bypass or Fan-Powered | Fits in tight mechanical rooms; avoids major duct modifications | May require minor duct reconfiguration; not ideal for steam models |
| Homes with Hard Water (Hamilton, parts of Mississauga) | Fan-Powered with Scale-Resistant Pad | Flow-through design reduces mineral buildup vs. drum-style units | Annual pad replacement recommended; consider inline water filter |
What If You Have a Heat Pump Instead of a Furnace?
Although heat pumps don’t dry the air as much as gas furnaces do, the winter air in Ontario is still very dry, frequently having an indoor humidity of less than 30%. It is definitely possible to install a whole-house humidifier if you have a ducted heat pump system. The procedure is almost the same: the humidifier uses the blower fan to distribute moisture after mounting to the air handler’s ductwork.
Whole-house humidification is not feasible, though, if your house has a ductless mini-split heat pump, which is typical in condos or retrofits. We advise high-capacity console humidifiers for the primary living spaces in those situations. To learn more about your options, check out our guide on sizing ductless systems for Ontario homes.
Humidifiers function flawlessly in hybrid systems (heat pump + gas furnace backup), turning on whenever the blower runs, independent of the heat source.
Signs You Need to Add a Humidifier This Winter
Don’t wait for cracked hardwood or bloody noses. Watch for these early indicators:
- Static shocks when touching doorknobs or light switches
- Wood furniture or flooring developing hairline cracks
- Dry, itchy skin or frequent nosebleeds, especially in children
- Houseplants wilting despite regular watering
- Feeling cold even at 21°C, dry air feels cooler than moist air
If your indoor humidity is below 30% (use a $15 hygrometer to check), it’s time to consider adding a humidifier. And remember: proper humidity lets you set your thermostat 1–2°C lower while feeling just as warm, reducing heating costs without sacrificing comfort.
DIY vs Professional Installation: What Can Go Wrong
Some try to install humidifiers themselves to save money, but common mistakes include:
- Skipping the drain trap, allowing sewer gas into living spaces
- Using improper water valves that restrict flow or leak
- Mounting on return ducts with insufficient clearance
- Miswiring to line voltage instead of 24V control circuits
- Setting humidistats too high, causing window condensation and mold
These errors can lead to water damage, poor performance, or even void your furnace warranty. That’s why we always recommend professional installation, especially when you’re investing in a system that affects your entire home’s air quality.
What You Need Before Installation Day
To avoid delays or extra charges, ensure these conditions are met before our technician arrives. Most Ontario homes already have these, but it’s worth checking.
Requirement | Why It Matters | How to Check | If Missing, What We Can Do |
|---|---|---|---|
| Cold Water Line Within 5 Feet | Humidifiers need a constant water supply | Look for a nearby pipe in basement or mechanical room | We can run new ¼” PEX line from nearest cold water source ($150–$300) |
| Floor Drain or Condensate Pump | Excess water must drain safely to prevent leaks | Check for floor drain near furnace or existing AC condensate line | We can install a condensate pump kit ($200–$350) if no drain exists |
| Accessible Ductwork Near Furnace | Mounting requires 12–18 inches of straight, unobstructed duct | Look for clear space on return or supply plenum | We can modify duct layout if needed (rare; adds 1–2 hours labor) |
| 24V Control Circuit Available | Humidifiers wire to low-voltage furnace controls, not line voltage | Most furnaces post-2000 have this; older units may need upgrade | We’ll verify during assessment; rarely an issue in GTA homes |
| Minimum 30″ Clearance Around Furnace | Ontario code requires safe access for maintenance | Measure space around unit, no stored boxes or shelves | Please clear the area before our arrival; we cannot move personal items |
Get a Humidifier Added to Your Furnace Today
We at Heat Flow HVAC make installing a humidifier in your current furnace easy. We can frequently finish installation the same day because we stock AprilAire, Honeywell, and GeneralAire units. Our certified technicians guarantee a secure, code-compliant, and efficient setup, whether you’re in Toronto, Hamilton, Oakville, Burlington, or any other location in the Greater Toronto Area.
Not only does adding a humidifier increase comfort, but it also safeguards your house, your health, and your HVAC system. Dry air makes your furnace work harder, stresses wood, and irritates lungs. Proper humidity will prolong the life of your floors and furniture, make you feel warmer at lower temperatures, and lessen static.
Are you prepared to permanently solve dry air? For a free in-home evaluation, get in touch with us. For more on indoor air quality upgrades, see our guide to how humidity affects AC performance in summer, and why year-round moisture control matters.