Reuben's Home Inspection Blog


Humidifiers Do More Harm Than Good

Whole house humidifiers can cause serious problems with houses, especially in Minnesota.  Sometimes they destroy houses.  This topic gets a lot of people whipped up, and I always hear the same arguments for having a humidifier: they prevent hardwood floors from cracking and splitting, they make the house more comfortable, you'll get nosebleeds if you don't... the list goes on.  I admit, those are all valid arguments.  Nevertheless, the damage caused by an improperly used humidifier can far outweigh the benefits, and humidifiers are almost never used properly.  From all the houses that I inspect in Minneapolis and the surrounding areas, I know this.

Whole house humidifiers are installed in the furnace ductwork, adding moisture to the air that gets distributed throughout the house.  The amount of moisture that's added is manually controlled with a dial that is usually located next to the thermostat or the furnace.  To maintain the proper level of humidity, the owner needs to know what the temperature is going to be, and then adjust the settings on the humidifier accordingly.  This is why I have such a problem with whole house humidifiers!  Here's an excerpt from an owner's manual:

"it is important to anticipate a drop in outdoor temperature and reduce the setting  accordingly to avoid excessive condensation. For example, with an outdoor temperature of 20°F the correct setting will be 35% RH. If the temperature is expected to fall to 0°F that evening, then merely reduce the setting to 25% several hours prior to the temperature change."

"Merely?"  Get out!  Nobody does this!  Ok, one person does.  A buyer's father attending an inspection got defensive about humidifiers when I told his son that I don't recommend them.  When I explained that most people don't use them properly, he said he adjusts his humidifier twice a day.  My jaw dropped and I told him I was impressed.  This is definitely the exception, and if you're one of the few that use a humidifier properly, give yourself a pat on the back.

The biggest problem with whole-house humidifiers is that too much moisture gets added to the air, Moisture Damaged Window and the moisture condenses on the windows, walls, and especially in the attic.  Excessive moisture in the home causes mold growth.  Excessive moisture on the windows stains the finish and damages the wood.  Excessive moisture in the attic causes condensation, which can rot the roof boards.  I've inspected many attics with rotted or delaminating roof boards, and in every case there was a whole-house humidifier present.  If you've read my previous blog about attic bypasses, you know how moisture gets in to the attic.

My recommendation is usually to not use whole house humidifiers unless you're an extremely ‘type A' homeowner, which means you'll check the weather forecast and adjust your humidifier all the time.  I do have a bit of good news about humidifiers though- the newest ones come with automatic humidity controls, so you don't need to adjust the settings all the time.  I learned about these at Aprilaire's web site, and I think they're a great idea that will probably save a lot of homes from damage.  If you must use use a whole-house humidifier, use one of these.

Reuben Saltzman, Structure Tech Home Inspections - EmailRobbinsdale Home Inspections

Reuben Saltzman, Structure Tech Home Inspections


Comment balloon 8 commentsReuben Saltzman • March 12 2009 06:43AM


I agree with you. In fact I've removed mine from the furnace and instead use free standing humidifiers when needed. A couple years ago I was inspecting a home and noticed water droplets on a closet ceiling. My first thought was a bad roof leak but I'd already performed the exterior inspection and the roof appeared to be in good shape. I also noticed a considerable amount of condensation on the windows, it was almost like they had been boiling water for a couple days. Once I entered the basement and made my way over to the furnace I noticed the humidifier was cranked up ALL the way.

Some SOP's state the humidifier is outside the scope of the home inspecition but I think it's more than worth educating our clients on how to use and maintain them.

Posted by Vince Santos, Southeast Michigan Home Inspector (StepByStep Home Services LC) over 11 years ago

I had no idea.  Thank you for this information.

Posted by Wendy Welborne-Kimery (Keller Williams-Lake Norman Mooresville,NC) over 11 years ago

Great tip. . thank you

Posted by Fernando Herboso - Broker for Maxus Realty Group, 301-246-0001 Serving Maryland, DC and Northern VA (Maxus Realty Group - Broker 301-246-0001) over 11 years ago

I've been getting sore throats from leaving a space heater on all night...and I thought a humidfier might be a good way to go. I guess I should focus on a small room humidifier instead of a whole house? Never would have thunk it. Thanks! Pittsburgh Personal Trainers

Posted by Organic Marketing over 11 years ago

Reuben, I couldn't agree more. Home owners all too often crank up the humidifier and let them go. Then question why they see mildew building up on their new vinyl windows.

Posted by Tad Petersen / Home Inspector, Mpls (Safeguard Home Inspections, Inc.) over 11 years ago

I love reading your blogs. You are a wellspring of knowledge I tell ya. Glad to see we don't use whole house humidifiers here in California.

Posted by Winston Westbrook (Westbrook National Real Estate Co) over 11 years ago

I just leave the windows open all the time. I figure Mother and Father Nature know what they are doing -- LOL.

Posted by Russel Ray, San Diego Business & Marketing Consultant & Photographer (Russel Ray) over 11 years ago

I usually recommend that they be removed. Such a small percentage of them are properly operated and maintained. I find it odd that introducing moisture to warm, dark, dusty ductwork would be a good selling point! But of course, this is not explained to a purchaser. Next to jacuzzi tubs - they are the biggest waste of money!!

Posted by Hank Richter (HomePro Inspections of RI) over 11 years ago