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In the winter, my house (~2500 sqft) becomes unbearably dry. Last winter, my wife and I used a tiny humidifier for the master bedroom to keep us from completely drying out, but since then I have been exploring a whole-house solution, complete with humidistat. It seems well within my ability to install it.

The trouble is, everywhere I've read that a whole house humidifier should not be needed. Normal humidity, they say, should be maintained simply by normal activity (showering, cooking, etc.). If the house is dry, it's far more likely to be that I have leaks (say, around my recessed lighting), and then adding a humidifier would risk mold issues.

So this is my dilemma: in order to find air leaks, everything I've read is that I'd need to have an HVAC guy come out with a blower door, which is very not DIY. So, expensive. Or, I could go boldly forth and just install the humidifier, in spite of the fact that I might not need it.

So, what should I do? Any guidance would be most helpful here.

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Do you have centrally ducted heating? (Kindof an important prerequisite for a whole house humidifier.) – msemack Nov 15 '10 at 13:26
Yes, thankfully I do. – Nate Nov 16 '10 at 2:58
up vote 24 down vote accepted

I went though a similar debate last year and ended up getting a whole house humidifier. I never remember reading that you should be able to get the humidity level to normal levels though normal means (shower, cooking, etc). In a big house, that is most likely not possible. Do you have a humidistat now, or does your stand alone unit give you a reading? I would recommend you getting one of those first to see how bad it truly is. If I remember correctly, if your humidity is below 30%, you could actually be causing harm to yourself and your home.

Our house approached 25%, which is dangerously low. Some of the driest deserts in the world don't get that low. For example, Las Vegas ranges from 21%-39%. You may be living in conditions that are way too dry.

All that being said, I knew we needed to do something. You mentioned worrying about mold, sure this could happen if you raise your humidity very high, but think about it, in the summer your home probably approaches 80%-90%. With humidity that hight, and the warm temperatures, that natural condition is more likely to produce mold than your 70 degree house in the winter. Plus, you will find just increasing your humidity to like 35%-40% with your whole house humidifier makes it very comfortable. AT that level, mold is unlikely an issue. The added bonus us that the more humid the house is, the warmer it feels. Again, just like in the summer, a humid 90 degrees is much warmer than a dry 90 degrees. We found we were able to decrease the temp of the house simply by adding a little humidity. Used to be 72 degrees at about 25-30% humidity, we now keep it at 70 and 35-40%. So we save heating costs there.

Ok, so what kind to buy? I researched the various types of whole house humidifiers, and it comes down to three types.

  1. Drum - These are the least expensive and easy to install. They install on your cold air return line, and use a motor and belt to essentially lift cold water from a drum into the the air and let evaporation and the passing air movement to pick up the moisture. These require considerable maintenance it has standing water and risk of mold due to the standing water. You have to replace the belt frequently. I opted to not get this one due to the standing water and maintenance issues.
  2. Flow Through - These can be installed on return or supply line. These are the middle of the road in cost and performance. Again, they also use evaporation, but you do not have standing water. There is a filter that water flows through (drip) and the air blows through the filter. The water however, needs to be drained, and new water is always trickling though. Since it always uses new water, the risk of mold is almost none. Uses no electricity, but does requires a water line and is always using new water.
  3. Mist / Steam - The most expensive, but most effective. They actually produce steam, rather than relying on evaporation. Because of this, you can more easily control the desired humidity. Can come in cold and hot water forms, injecting hot or cold steam into your supply line. Requires both electricity and a water supply line. Risk of mold is low due to no standing water, but the hot steam could cause issue in your ducts if you run it too often and too high I imagine.

I opted for the steam model, mainly because of the low maintenance and ability to control the desired humidity more easily. I installed it in an afternoon, it was easy to do. Most of them come with high end humidistat / thermostat, that would replace your existing house thermostat. Then the system knows how to control the furnace to optimize the output. I went with the Honeywell TrueSTEAM series and it has worked great. Good Luck!

Here are a few other descriptions:



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I agree with you. I find it pretty hard to believe that showering and cooking would produce enough humidity for a whole house, as each of those activities typically only produce humidity for <30 minutes per day. If you have an exhaust fan in your bathroom, and a non-recirculating fan in the kitchen, most of the humidity is getting sucked outside anyway. – msemack Nov 15 '10 at 13:36
@mohlsen, the thought hadn't occurred to me to get a humidistat first. That's something I could derive a benefit from either way. Do you have a combo unit (thermostat/humidistat) that you could recommend? Also, the TrueSTEAM was the series I was eying... do you know a good source for these? I could not find one online the last time I looked (which, admittedly, was a little while ago now). – Nate Nov 16 '10 at 3:01
My stand alone humidifier had a humidistat before i got the whole house, and now i use the humidistat / thermostat that came with the TrueSTEAM, so unfortunately, i dont have any recommendations. What do you mean by sources? Like where to buy one or where you can read up on them? – mohlsen Nov 16 '10 at 13:01
I got mine here from pexsupply.com. Wasn't the cheapest but with free shipping, it was the lowest code in total. Was delivered quickly. Went with the 6 gallon model for my 2500 sq ft house. If I were to do it again, probably would have gone with the 9 gal as it run frequently. – mohlsen Nov 16 '10 at 19:03
"cold steam"? Isn't steam hot, by definition? – Ken Liu Nov 16 '13 at 3:31

The blower door test is not too bad. I had an eco energy audit done, which includes a blower door test among some other visual inspections, and that was $150.

Fixing any leaks will help with your humidity, as well as help with your heating and overall make your house more comfortable.

I'm not sure if it will totally replace the need for a whole-house humidifier or not though, but it doesn't hurt (aside from the cost for the test, anyways).

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Another suggestion, which is unfortunately not DIY is a thermal imaging scan of your house. They basically take video of your house with an infrared camera and it captures heat loss as color variations. The cost is comparable to the blower test. Here is a link to a sample thermographic inspection.

This may be one of those times where DIY isn't the best approach for detecting the issue. FIXING the issue could definitely be a DIY approach (I.E. adding more insulation, caulking etc.) but in terms of actually detecting the problem, there are some specialized tools that professionals have that could really make the job of detection much easier.

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4 years later, thermal cameras are available for rental in the vicinity of $100 per day, making DIY potentially doable. – Foo Bar Dec 8 '14 at 21:10

The problem with adding humidity to a leaky home is amount of water vapor air can hold varies significantly with temperature.

While 30% relative humidity at 72°F seems dry and harmless in and of itself if you cool this same air to 38°F (let alone -10°F it sometimes get) all of the sudden you have reached 100% RH. The difficulty is making sure condensation of water vapor is not likely to occur within walls of your home where it would be difficult for anyone to notice accumulations of moisture.

Least insulated portion of homes are typically our windows and so first indication of too much humidity for outside conditions is condensation of water accumulating on windows however this is not always true. Modern double/triple pane windows offer more insulation and raise risks that air leaks/missing insulation insides of walls may become first condensing surface before meaningful condensation is noticed on windows.

As outside temperature drops so does amount of humidity your building can safely support! We live up north in a well insulated home with a humidifier. When things get really chilly we still have to accept some level of discomfort. Using the outdoor temp sensors/frost protection features of control electronics is a good way to mitigate risks associated with allowing too much humidity for conditions and associated risks of mold/rot problems.

Other risks come from water damage from equipment/maintenance failures. Saddle valves are garbage never use them. Have a line plumed if there is not one nearby. Turn off water supply when away and at end of heating season. If you have an evap humidifier buy several pads up front and make sure they get changed once a year. Leak alarms (harbor freight) are free insurance. Mount evap units on return side if possible so if there is a failure and water leaks it does not leak into the furnace blower motor and control board. If located in the attic consider potted plants instead of a humidifier.

No more bloody knuckles/noses is worth a lot around here and so no regrets with overall decision understanding it is a responsibility.

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I am a licensed contractor, home inspector and certified energy auditor.

Energy audits using blower doors in conjunction with infrared is ideal for air leakage that leads to heat and humidity loss and increased energy costs. The whole house humidifiers can be very problematic and can shorten the usable life of your furnace.

I have been on countless home inspections where these units are abandoned in place while the return air plenum is corroding and the blower compartment is plagued with heavy rust. On the inspection I did today the blower compartment had black mold.

These units are not "install and go" as advertised. Just like a portable unit needs cleaning and maintenance these systems do as well. People generally don't do that maintenance and they lower the quality of air leading to more serious health issues while prematurely aging their furnace. Do your due diligence and read the manufacturer's maintenance schedule before considering this option.

If you seal your internal heat envelope with the correct vapor barrier levels your moisture levels can be maintained by normal living activities with the minimal assist needed by a portable unit.

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It would be nice to know the true conditions on which the statement that normal living can produce sufficient humidity in the winter. I suspect it is based on a family of 4 with at least 2 large panting dogs and a 50 gallon aquarium or two. My house has Superior Walls [TM] (precast 5000 LB concrete), with triple glazed E-glass windows. The concrete walls are waterproof, not to mention wind proof. They are 10 inches thick and fully insulated. The blower door test showed that, under the test conditions, my house's air exchange rate was over 12 hours per exchange - off the charts. – user30097 Dec 28 '14 at 4:21
The heated house is about 2600 sqft. I am the sole inhabitant. I cook, bathe (whether I need it or not) an respire moisture into the air by breathing. The house is in SC. The house regularly gets to 30% RH in the winter, notwithstanding all of the above. Part of the reason is that I run a woodstove at night when the heat pump is not efficient. There is an outside air vent which can draw air in by the vacuum caused by heat up the flu, but can not let air escape (reverse flow). The heat pump has a separate fresh air intake on the return side. – user30097 Dec 28 '14 at 4:21
All of these factors impinge on the RH. But significantly tightening up this house is not possible. Stating that daily living provides enough moisture if the house is tight is false. In fact, when the RH is 80% or more outside, the RH in the house does not change more than a couple of percentage points regardless of the heating system in use because the house is so tight that the high outside humidity (think 24 hours of rain) can not get into the house. Again, saying that just living in the house should be sufficient to maintain RH begs the facts and ignores a host of factors. – user30097 Dec 28 '14 at 4:21
Sorry about the stream of comments here; this was originally posted as a response to your answer, and since it wasn't answering the original question, I converted it to a comment on your post. – Niall C. Dec 29 '14 at 4:06

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