Is a Humidifier in an Airtight House Ever Needed?
![Static Electricity Can Happen When The Indoor Humidity Is Very Low. But Do You Ever Need A Humidifier In An Airtight House? [Photo By By Dave Fayram, CC BY 2.0]](https://www.energyvanguard.com/wp-content/uploads/2026/01/static-electricity-low-humidity.jpg)
In our HVAC design work at Energy Vanguard, we sometimes try to talk people out of things. I’ve discussed this in regards to makeup air systems for range hoods, but today let’s look at a different one: humidifiers. We don’t include this in our scope of work. If you think the indoor humidity is too low, you could put a humidifier in an airtight house, but you should be cautious in doing so. It might create more problems than it solves.
What’s the right indoor humidity?
I covered this question a while back, but let me recap it here. There is no magic number for “the best” indoor relative humidity. Nor is there one for dew point, which is generally the best metric to use. As I wrote in the other article, it depends on several factors.
That’s why you’ll usually see a recommended range in which to keep the relative humidity. But even that range isn’t hard and fast. Excursions outside the range are OK as long as they don’t last too long.
A good range for indoor relative humidity in winter then would be 30 to 45 percent. But you’d better have a really good building enclosure with triple-pane windows if you want to attempt 45 percent in a cold climate.
What do experts say and do?
In the 1980s, a research paper claimed that the best range for indoor relative humidity is 30 to 60 percent. You may well have seen a version of the graph they included. It’s called the Sterling chart and the one I had made for my book is below. (For more background on this, see my article on that paper.)
Dr. Stephanie Taylor, a medical doctor with a degree in architecture, says that data from hospitals show that 40 percent should be the lower bound of the range, not 30 percent. I heard her say on a podcast that she uses a humidifier in her Vermont farmhouse to maintain a minimum of 40 percent relative humidity. That seems a bit scary to me, but she didn’t say what she’s done to improve the enclosure.
Gary Nelson, founder of The Energy Conservatory, lives in Minneapolis. You may recall that I wrote about how he heats his home with a heat pump that has no auxiliary heat. I called him this week, and he told me he never uses a humidifier in his home. Even so, his relative humidity stays between 30 and 35 percent in the coldest parts of winter. He’s got a great building enclosure with triple-pane windows and minimal air leakage, so he can stay at 30 percent or above without a humidifier.
Then I put the question to Lew Harriman, who made a career of investigating and writing about moisture problems. He said that he’d never say never to putting a humidifier in an airtight house. If you’ve got a building enclosure that can handle it and you don’t try to keep the indoor air too humid, it can work.
Why might the humidity be too low?
Occasionally, a client of ours will come back to us after the house is occupied and ask about adding a humidifier. We follow up with these questions:
- How airtight is the house?
- What ventilation rate are you using?
- Are you using an energy recovery ventilator (ERV) or a heat recovery ventilator (HRV)?
Airtightness is hugely important because every cubic meter of cold outdoor air that infiltrates the house dries out the indoor air. Cold air is dry air, you know. The more airtight the house, the less you have to worry about humidification.
The ventilation rate matters a lot, too. If it’s too high, it also can dry out the house. I spoke with a client in Seattle recently who was complaining of low humidity. He should have been running his ERVs at 180 cubic feet per minute (cfm) in total but instead had them maxed out at about 400 cfm. When he turned them down as I suggested, the indoor humidity was fine.
Then there’s the issue of the type of whole-house ventilation system. As I’ve written, most houses should have an ERV, not an HRV. An HRV will dry out the air as much as infiltration because it does no moisture recovery.
So, before you jump to the conclusion that you need a humidifier in an airtight house, check out those things.
3 types of humidifiers
When I spoke with Lew Harriman, the issue of humidifier type came up. He has a preference, which I’ll tell you below. First, here are the three types:
- Evaporative humidifier – Warm air blows over a wetted pad, evaporating water into the airstream. This type can get a bit nasty inside, especially if it doesn’t get cleaned regularly.
- Steam humidifier – Add heat and boil water to humidify the air. It takes more energy than the evaporative type.
- Ultrasonic humidifier – Ultrasonic vibrations create a fine mist to increase humidity. But if you don’t use pure water, whatever else is in the water ends up in the air, too, so you can get a boost in particulate matter as well.
Harriman says he would recommend the steam humidifier because it stays cleaner than the evaporative type and doesn’t add to the particulates the way an ultrasonic humidifier can.
A simple way to determine the right indoor humidity level
OK, let’s boil this down to an easy test you can do. If you’re thinking of putting a humidifier in an airtight house, you should start by measuring the indoor relative humidity. Thirty percent or higher is good. More than 45 percent is probably too high.
Now, here are those real-world tests:
- The humidity should be high enough that you don’t have a static electricity problem.
- The humidity should be low enough that you don’t have more than a bit of condensation on the windows, and it doesn’t start dripping down the way you see above.
And again, excursions outside those bounds can be OK if they don’t last long. If you have a constant problem with condensation on the windows, you may be in danger of rotting the building. Harvard found that out the hard way. (Yeah, I wrote about that, too.)
Lagniappe
Since this is winter and I’ve mentioned static electricity, you also ought to know that this Friday, 9 January, is National Static Electricity Day.
Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and is the author of a bestselling book on building science. He also writes the Energy Vanguard Blog. For more updates, you can follow Allison on LinkedIn and subscribe to Energy Vanguard’s weekly newsletter and YouTube channel.
Photo at top by Dave Fayram from flickr.com, used under a Creative Commons license (Dave Fayram, CC BY 2.0).
Related Articles
What Is the Best Indoor Relative Humidity in Winter?
Controlling the Humidity in Your Home in Winter
Bad Advice About Indoor Humidity in Cold Weather
A Humidifier Is a Bandaid — The Problem Is Infiltration
Comments are welcome and moderated. Your comment will appear below after approval. To control spam, we close comments after one year.
This is a solid enclosure-first discussion, but I think one important variable is missing: occupant physiology, not just enclosure durability.
A technical datapoint from my own home may be relevant. My wife had chronic recurrent epistaxis (daily nosebleeds) prior to a deep retrofit we completed in 2013. At the time, we were focused entirely on energy—cutting leakage (~⅔ reduction), right-sizing cooling, and correcting airflow. We did not expect a health outcome.
Pre-retrofit:
• ~8 tons of cooling on ~2,900 ft² in a hot-dry Northern California climate
• Severely low airflow (well below dry-climate targets)
• High envelope leakage
• Result: extreme over-drying of already dry outdoor air
Post-retrofit:
• 2 tons of cooling
• >500 CFM/ton airflow (dry-climate appropriate)
• Much tighter enclosure
• Balanced ventilation via HRV
Several months after the retrofit—after utility savings were already tallied—we realized her daily nosebleeds had stopped entirely. The only meaningful change was that we had taken control of indoor moisture dynamics: eliminating excessive infiltration, correcting airflow-driven latent stripping, and ventilating in a controlled, balanced way.
Winter adds another wrinkle. We keep the house cool year-round (~65°F average). Even though lower temps raise RH for a given moisture content, absolute humidity is still low in cold, dry climates. In that condition, we use a small evaporative pad humidifier with distilled water, targeted and limited, with no condensation risk to the enclosure. It has been highly effective for nasal comfort without pushing bulk RH upward.
One hypothesis I’d offer—consistent with clinical observations—is that as we remove chronic respiratory irritation (dust, over-drying, pressure-driven infiltration), occupants can actually become more sensitive to low absolute humidity. Similar to how skin heals and loses callousing, nasal tissue may recover and demand narrower moisture bounds. Travel (hotels, airplanes) makes this contrast very obvious.
So while I agree that humidifiers should never be a default—and that enclosure safety sets the upper bound—I’d argue there’s a legitimate, technically defensible case where localized or modest humidification improves occupant health without endangering the enclosure, especially in cold-dry climates with well-controlled ventilation.
In short: “Is a humidifier ever needed?” depends not only on dew point at the window, but also on what’s happening inside human nasal passages.
PS- Love that you got to talk to two of my favorite people in the BS world for this article!
Mike: Thanks for raising the issue of individual physiological variation. That’s an important factor as well, and you’ve added some great info with data to back it up. What relative humidity and dew point ranges does your house stay in now?
Mike, with 8 tons of cooling in a leaky northern CA 2900sqft home it seems that your wife’s health condition was greatly aggravated if not directly caused by the severe indoor drying. A health outcome was inevitable with your retrofit.
When I started building 20+ years back, my main motivation behind chasing building science principles was the built environment’s impacts on human health, and I almost couldn’t care less about the health of the building enclosure at the time. Yeah, I made some minor mistakes, but the driving principle for me remains human health.
Winter humidity issues in NC are generally found when nosebleeds occur. We have been successful resolving “winter nosebleed problems” in NC which appears only to occur in two scenarios:
1) older leakier homes
2) newer (1995 and later) homes with “fresh-air-intakes”
Our solution to problem #1 is to perform BOTH attic-air-sealing and duct-sealing, in addition to providing at least a “bare-minimum sealed-crawlspace”, and if the home is on slab, pulling back the carpet if applicable around the perimeter of the home, and sealing the bottom-plate to the slab which is a surprisingly leaky joint. This combination of Exfiltration and Infiltration limitation is bueno.
Our solution to problem #2 is to simply install a 6″ duct-cap on the plenum-side of the fresh-air-intake, often ignoring the greater building-envelope solutions until we have been notified that another intervention is needed.
I like to remove penetrations: 2in1 washer/dryer doesn’t need vent, radon piping stays outside air barrier, etc.
this should make interior variables easier to control
I use free humidification when needed which can also result in reduced overall energy use in the winter. I have a humidity sensor in my bathroom and when the RH is below 35%, I don’t run the exhaust fan during showers. I have never had a problem with condensation on any surfaces, but I do keep an eye out for that. When I used to live further north, I set up the clothes dryer to vent indoors when the indoor humidity is low in winter. Of course, this was an electric dryer; I would never do this with a gas dryer. I put an additional lint filter on the dryer vent and it seemed to work well. Again, I kept an eye out for any surface condensation which wasn’t a problem as long as we left the laundry room door open.
I haven’t quantified how much more comfortable the house is with these measures, or how much energy might be saved, but everything is at least in the right direction. It does take a bit of thought on the occupants part to properly control this, but maybe someday we can automate these strategies.
On a more nuanced subject…not all homes need humidification but some rooms might…over the years I have humidified my music rooms ( guitars and piano) and rooms that held other moisture sensitive items ( any fellow decoy collectors out there?) …I’m with Lew and have only used stream in my homes and those of my clients.
On the same note on nuances … not all homes need dehumidification but some rooms might…I had a drying room for my outdoor gear that used a radiant wall with an HRV …
As others have noted… it depends.
Easy right? [;@)
Robert: Pianos are an interesting case. We bought a grand piano in the 1980’s for my wife. The store said that we should put a humidity controller under the wooden sound board to keep it from swelling in the summer and cracking in the winter. I can’t remember what it cost, but it seemed too cheap to be able to control humidity all year. After they installed it, I took a look at it. It was simply a pan of water under the sound board with two electric heating elements: one in the water and one above the water. It had a relative humidity sensor and when the humidity was too high, it would heat the air above the water, thus lowering the RH. When the humidity was too low, it would heat the water, thus raising the RH. It also had a float sensor with a light to tell us when to add water. To me, this is was an ingenious invention and since I was teaching psychrometrics at the time, it made a lot of sense. We still have that piano 40 years later (along with my wife) and have had no problems with sound board cracking even though that piano has been in Minnesota, East Texas and several states in between.
Happy New Year Roy,
Same here on the piano though filling it with conditioned water was a bit of pain…there was a funnel and tube connected to a reservoir that was out of sight so occasionally during filling the reservoir … I can’t say if having the room humidified reduced the frequency of the piano humidifier… it did a great job with the guitars though and a few other items sensitive to moisture content.
Cheers
Robert, our piano humidifier had the fill tube next to the low-level light on the edge of the piano. It came with a special water bottle that fit on the tube so that you didn’t need a funnel. Very clever. I am not sure if my wife uses conditioned water or if she cleans the pan out periodically. I will have to ask her.
It would be interesting to monitor the energy consumption of this to see how often it has to heat the water vs. heating the air.
To me, the most interesting aspect of this piano humidifier/dehumidifier is that it is simple, low-cost, low-maintenance, and appears to be quite effective. This is engineering at its best. During my long career in this industry, I mostly see new concepts that are more complex, more expensive, less reliable, and with questionable performance.
Hi Allison, thank you for another timely and helpful article. I find the “Optimal Zone” chart a useful way to visualize relative humidity effects. One question I had, though, is about the absence of dry-bulb (and related wet-bulb or dew point) temperature in the chart and discussion.
Since relative humidity is dependent on temperature, I was curious whether a specific dry-bulb range is being assumed, and how you recommend readers think about comfort or moisture risk without that context. I’d appreciate any clarification. Thank you.