Bypass humidifier on supply or return

A central or whole-house humidifier is generally mounted on a forced air furnace (gas or electric) or heat pump. While the actual path of air flow may differ depending on the type of model, the general idea is to take warm air from the furnace or heat pump, pass it through the humidifier unit where it will increase in humidity by contacting the humidifier's evaporative surface, and to then pass the air back into the central heating ducts for distribution of the warm, more humid air, to the home. The most frequent installation configuration is of a by-pass humidifier. The humidifier is generally mounted on the cold air return plenum. A portion of the warm air from the furnace's hot air supply duct is directed into a flexible duct, usually about 6 inches in diameter, which is connected to the humidifier on the cold air return duct. The air travels through this flexible duct, into the humidifier, back into the cold air return duct and into the furnace where the furnace fan re-distributes it to the home. Simple and effective...

Since humid air will tend to release its humidity when it comes into contact with cold objects, it is generally not recommended that a central furnace humidifier be used in conjunction with a central air conditioner. When the humid air reaches the air conditioner coils (which are very cold), it could cause excessive condensation. On the bright side, very few homes require humidification during the summer months or air conditioning season anyway since warm summer air generally already has a high capacity to hold moisture. Cold winter air, even when the relative humidity level is high, holds limited actual moisture.

Both the bypass humidifier and the power humidifier have the same task at hand – to add moisture into the air of your home. Both do that by working in conjunction with your furnace or air handler, but there are some major differences in how they deliver the humidity to the rooms of your house.

The bypass humidifier is connected to the return of your furnace or air handler. It does not have a motor of its own and instead relies on the blower motor of the furnace to push warm air through it. The warm air is then pushed through the water panel that is within the humidifier and absorbs moisture from it. That moisture is then delivered back into the air stream and back into your home.

The bypass humidifier is probably the more common of the two, but the power humidifier is quickly gaining popularity and is replacing many bypass humidifiers in many of our customers’ homes.

When comparing the power humidifier to the bypass humidifier, the major differences are that it has its own blower motor and does not rely on the furnace blower motor. The fan delivers moisture to the supply, which sits above the heat source. Once humidity is created it is sent through the ductwork to the rest of the house and does not have to recirculate through the furnace and heat exchanger, as is the case with the bypass humidifier.

Let’s look at some of the pros and cons of each.

Bypass Humidifiers

Pros

A bypass humidifier is more affordable, it adapts to various water types (i.e. hard, soft) and requires very little maintenance.

Cons

It has to be connected to a bypass duct, which is aesthetically unpleasing and unfortunately can eat up more space. Also, since it uses the blower motor of the furnace the humidity that it creates has to be redistributed back through the furnace and heat exchanger again and again in a continuous loop. Therefore, a notable amount of moisture and humidity is lost. In other words, it is less efficient than the power humidifier.

Power Humidifiers

Pros

The power humidifier produces more humidity than the bypass humidifier. In fact it creates about one gallon of humidity more per day than the bypass humidifier. Another pro is that it can humidify more square feet and is ideal for larger homes.

Cons

The one downside to a power humidifier is that it is much more expensive to repair than the bypass humidifier.

We hope that this information is helpful in choosing the right whole-home humidifier for you and your home. And if you have any further questions please feel free to contact us. HVAC Parts Shop is here to help!

"I have a heat pump that came with the house. I am the original owner.

A few years ago I had a HVAC company install a opens in a new windowBryant HUMBBSFP humidifier.

It was installed BEFORE the heat pump as the air flows. I believe it does not add humidity to the house because the heat generated by the heat pump immediately dries out all of the moisture.

I believe it should be installed AFTER the heat pump so the air will retain the moisture.

Am I correct saying the location is critical? Should it be before or after or does it not make a difference?

Also, this is a very bad design. I have replaced the pad, but it took an hour. It took a technician about 1/2 hour. That is too much time."

Here's my answer: CAPS below for emphasis, not SCREAMING. 🙂

Larry, I know you may think I'm being a smart A * *, but it doesn't matter how I feel it should be installed, nor any other person at any other website. I do know the answer, but what I'm going to recommend is that from now on you don't ask folks like me.

If you want to know exactly the best way to install any product, you do but one thing.

You READ the written installation instructions that come with the product. Period.

If you want to make sure you discover the BEST COMPANY or TECHNICIAN or CARPENTER or PLUMBER or ROOFER to install products you buy, you READ the written instructions BEFORE you GET BIDS. Why?

You want to be able to ask questions of the bidders to see if THEY KNOW the RIGHT WAY to install the product.

Yes, this is work. Yes, this is a royal PIA. Yes, you would think that you can TRUST the mechanics to do it right.

But you CAN'T. You need to do your due diligence if you want to make sure things are done right.

Here's another reason why you have to do it this way.

Most product warranties are VOIDED if you don't follow the instructions!

Okay, here's your answer. My guess is the written instructions will show it's best to put that humidifier on the SUPPLY SIDE of the ducting system. Why?

Warm or hot air can absorb MORE MOISTURE.

Finally, you want to make sure the idiot installer didn't tap a nearby water line with one of the USELESS saddle valves. NEVER use one. Currently your humidifier could be starved for water because of the horrible saddle valves.

You want to install a proper tee fitting in the water line, put in a ball valve shut off and then the reducing fittings for the 1/4-inch soft copper or other supply line to the humidifier.

I hope this helps you.

If you're a person who bet me on whether you'd know my exact answer and got it wrong, it's time to PAY UP. 🙂

I say this especially if you discovered something here in this post that will save you a TON of money in the future.

Does a bypass humidifier go on supply or return?

Where should a bypass humidifier be installed?

Does humidifier go on return air?

Can Aprilaire humidifier be installed on return duct?