7 Best Furnace Humidifiers For Existing Home HVAC Systems (2024)

Written By

Ile Kauppila

Expert Reviewed By

Josh Mitchell

Last Updated On

January 30, 2024

This capable unit simply provides a value balance between capacity, reliability, and price that’s hard to beat.

During my tests, AprilAire 500 increased indoor relative humidity from an atrocious 15% to a healthy +30% in a couple of days.

It only took that long because the interior of the house had completely dried and needed to absorb the moisture.

AprilAire 500 ships standard with anautomatic control panel and humidistat.

With both an outdoor temperature sensor and an indoor humidity sensor, the controller determines the ideal humidity levels on its own and activates the humidifier accordingly.

It’s a simple set-it-and-forget-it solution.

As a nice touch, AprilAire has included a ceramic coating on the moisture padsthat slowly washes away during use, preventing bacterial and mold growth.

I suggest using a transparent drain tube, though, so you can make sure the melted material doesn’t clog it.

This humidifier has a couple of features that make installation simpler.

• The unit has areversible design, allowing you to install it upside down in case you want the bypass duct on the right-hand side.
• Thishumidifiersworks with both hot and cold water, although I recommend using hot water for ideal evaporation.

It's possible to mount the humidifier yourself, but I strongly suggest opting for professional installation.

The unit isn't very easy to install (partly because of the lackluster manual), and DIY installation will void its nice five-year warranty.

Hiring an HVAC professional is well worth it, though. AprilAire 500 is a solid, well-built humidifier that can serve you for years. It’s popular for a reason.

If the capacity of theAprilAire 500isn’t quite enough for you, don’t fret.

The 600M model from the same company can increase humidity levels in large homes — at an even lower price.

AprilAire 600M has one of the largest coverage areas on my list, losing only to theAprilAire 800steam unit.

That's particularly impressive, considering this model with a flow-through design has no fan to help it out.

This unit israted for up to 5,000 square feet, assuming your home is tightly insulated.

I didn’t have a space that big to test it in, but the AprilAire 600M brought the indoor humidity to 38-40% in a 4,000-square-foot space within a few hours and steadily maintained it.

Water supply isn't an issue since theanti-mold coated water panelswork with cold and hot water.

The biggest difference between the AprilAire bypass units is the control. The 600M is a manual humidifier with only an indoor sensor.

That said, if you already have a smart, automated thermostat (like Nest or Ecobee), you can hook the 600M to it without extra components.

It's best to let an HVAC professional do that, though.

As with the500, I wouldn't call the 600M easy to install, and DIY work will void the five-year warranty.

Additionally, you'll have to buy the mounting kit separately, which adds a few dozen bucks to the price.

Fortunately, the 600M is still affordable even with the added cost. If you need strong humidification but are on a budget, you can’t do much better than this.

Steam humidifiers boil water with electricity and send the resulting steam into the living space to effectively eliminate dry air.

Thanks to this working method, the AprilAire 800 rocks thestrongest humidifying capacity on my list.

It can emit23 gallons of moisture per day to humidify homes up to 6,200 square feet.

During my tests, the unit maintained the indoor relative humidity level at an unflinching 40% in a 4,000-square-foot space.

Yet, this unit works for small homes as well, withflexible operation options. It can plug into both 240V and 110V outlets.

With the latter, the moisture output falls by roughly half, which can prevent over-humidification in small houses.

Although this unit is a furnace humidifier, theoptional fan packagelets you mount it even without an HVAC system.

Like theAprilAire 500, the 800 steam unit is anautomatic humidifier.

Its dual sensors can monitor both outdoor temperature and the moisture level of indoor air, and it provides convenient digital control to maintain optimal humidity.

Steam units can sometimes be noisy, but this humidifier runs quietlyand won’t bother you with incessant hissing and burbling.

Although this unit is relatively easy to install compared to the bypass AprilAire models, so it can be mounted as an (advanced) DIY project.

The AprilAire 800 is also very expensive and — like the other AprilAires — doesn’t come with mounting hardware.

You must also regularly purchase new water canisters to prevent calcium buildup (as with all steam units).

In addition, I recommend spending even more money on a water hammer arrestor since this unit tends to experience water hammer damage with even average water pressures.

In the end, though, the superior humidifying capabilities are well worth the price in my books.

I tested it in a 3,500-square-foot space, and it raised the indoor relative humidity from 25% to 40% within 24 hours. Not shabby at all.

Like theAprilAire 600, this unit comes with astandard manual controller, which requires you to change the settings according to the outside temperature.

That said, as the AprilAire, the Honeywell can wire into an existing automatic thermostat.

Consider keeping the manual controller, though, since it has anaccurate and sensitive humidistat.

It might be even a bit too sensitive — small adjustments can result in big changes in relative humidity, so don’t be heavyhanded with it.

As a powered unit, the Honeywell can combat dry air without active forced air heating systems.

Of course, the fan does produce some noise and consumes more energy than simple bypass humidifiers.

Compared to bypass units, the Honey iseasy to installas it doesn’t need a bypass duct.

It’s a much more feasible DIY projectas you only need to cut an opening to your warm air supply and hook up the electricity and water connections.

You won’t really have to worry about the warranty, either, since the unit comes with only a one-year warranty.

With all that said, I suggest hiring a professional for the electrical connections (unless you're one yourself).

The manual's wiring instructions are… Well, I'd call them a joke, but I sure didn't laugh.

Fortunately, you can afford the electrician’s fee thanks to this unit’s low price.

Once you get the wires hooked up, you’ll have an effective and reliable whole-house furnace humidifier ready to serve you for years.

Perhaps you like the idea of being able to maintain the humidity level in your homewhether or not you’re running your heating system, but you’d prefer a more high-end solution.

In that case, GeneralAire 1000A is the belle of the ball.

This fan-assisted humidifier can produce18 gallons of moisture daily, providing powerful humidity control on par with the Honeywell Home powered unit.

Itscoverage area of 3,000 square feetisn’t quite as expansive as its rival’s, but I found the GeneralAire humidified the air more efficiently within its limited area.

I successfully produced a comfortable living environment with a humidity level of 40-45% in a leaky, 40-year-old, 2,000-square-foot house.

And that was with a huge wooden piano sucking up moisture in the living room.

In medium-sized and smaller homes, the GeneralAire packs a serious humidifying punch.

Unlike the Honeywell, this unit has anautomatic control panel with a digital display and dual sensorsfor monitoring indoor and outdoor air.

The humidistat is the most accurate I encountered during my tests, beating even the Honeywell’s.

If you’re looking for extremely precise humidity control, look no further.

That said, the GeneralAire can function as a manual and automatic humidifier. If you prefer controlling this whole-house humidifier yourself, you can do it.

The GeneralAire unit is fan-powered, so it can pump moisture into your home during any season.

Thefan is very quiet, and I wasn't able to hear it during normal operation unless I was specifically listening for it.

Since it doesn’t need extra ducts, the GeneralAire is reasonablyeasy to install.

However, I advise against doing so yourself for one reason —the 10-year warranty.

GeneralAire offers an incredible decade-long guarantee on the unit. Self-installation will void that warranty, so don't let it go to waste.

This unit is rather pricey and — like all powered models — can somewhat raise your energy bill.

It’s also a bit bulky, so it might not fit in the tightest utility closets.

Overall, however, this humidifier is a worthwhile investment for changing humidity levels all year long in medium-sized homes.

With a long warranty, you’ll have a long-lasting companion to improve your air quality.

A furnace humidifier can really contribute to good air quality in your home, but do they all have to be so difficult to install?

No, they don’t, and Honeywell HE280 is proof of that.

This unit has an unpowered flow-through design, so you will need to install a bypass channel from the return air duct to the warm air supply side.

However, you can avoid possibly the most complex part — wiring.

The HE280 has a damper air pressure switch that activates the unit when it senses flowing air.

The installation manual is also nicely detailed (as far as whole-house humidifier manuals go).

This unit has a dailymoisture output of 17 gallons, matching theAprilAire 600.

The coverage area is on par as well — I was able to keep a 2,500-square-foot, two-story home well-humidified and even raised relative humidity by 10% in a maximum rated 4,000-square-foot house.

Another thing I appreciate about this unit is that it needsminimal maintenance.

The machine distributes water more evenly across the water panel than others I reviewed, which reduces mineral deposits and helps the moisture pad last longer.

I want to give one word of caution, though:

• Due to its self-contained damper pressure switch, this unit uses a DC solenoid valve instead of an AC solenoid found on other models on my list.
• The DC valves are much more expensive and difficult to find if yours breaks.

As such, I recommend installing a scale filter between the water supply and the valve.

You can afford this extra part as the humidifier itself is fairly reasonably priced.

Granted, installing the extra filter complicates the installation process a bit. Luckily, this unit is so easily mounted that it won’t matter much!

Drum humidifiers can provide more efficient humidity than bypass models but generally require more extensive maintenance.

Desert Spring evens out the balance with itsunique rotating disc configuration.

Instead of relying on a rotating water panel that gets easily clogged with minerals and bacteria, Desert Spring draws water from the water reservoir with flat plastic discs.

Heated air blowing over them evaporates the water and pushes it into your home through the ductwork.

This operating principle gives Desert Spring a14-gallon daily moisture output and a 3,200-square-foot maximum coverage area.

However, I found the actual performance to be above the rated capacity.

Even in a 3,500-square-foot house, I had no issues keeping the relative humidity levels at a consistent 40%.

This whole-house humidifier punches above its rating.

Due to the solid plastic construction and no water panel, Desert Spring ischeap and easy to maintain.

If you'd like to simplify maintenance, you can invest in theoptional auto-flush systemthat drains the reservoir at set intervals.

Flushing the reservoir prevents mineral buildup, mold, and bacterial growth, which can help control asthma and allergy symptoms.

Desert Spring also hasa transparent cover, so it's easy to see when the discs need a wipe with a quick glance.

The ease of maintenance and solid construction make this a very durable unit (as long as you remember to keep it clean).

This humidifier model has actually been on the market for close to two decades.

Although it’s received some updates, the basic structure has remained unchanged. Why reinvent a wheel that just works?

As a final highlight, Desert Spring isvery quiet for a drum humidifier. It's also compact and lightweight, fitting in a small utility closet.

Apart from not having the output to humidify indoor air in huge mansions, there’s little about Desert Spring not to like.

It maintains healthy whole-house humidity levels without issues — what more would you want?

Frequently Asked Questions

1. https://www.healthline.com/health/humidity-and-asthma
2. https://www.just-humidifiers.com/humidification-energy.php
3. https://www.just-humidifiers.com/humidifier-sizing.php
4. https://www.epa.gov/mold/mold-course-chapter-2