AprilAire Humidistat

[Buck Turgidson]

I have an AprilAire. It seems that when I turn the humidistat to the point of right where it clicks on, the humidifier runs with each and every furnace cycle. If I turn it until it just clicks off, it never runs with any furnace cycle.

I guess I would expect that setting it right at the brink would make the humidifier run occasionally. But my house goes from either being a desert, to having moss and ferns growing on the walls.

Should it behave like this, or do I need to replace the humidistat? I would be interested in hearing from other AprilAire owners.

I have the model that sits on the cold-air return side. The humidistat is also on the cold-air return duct. Maybe that's part of the problem. Maybe it should be on the hot side.

[Joseph Meehan]

You really need to check the installation manual to determine how that should be set up. On mine the sensor is not a humidity sensor it is a out side temperature sensor that reduces the humidity setting when the temperature outside gets cold to avoid condensation on the windows. Your owners manual should give you some information as well. Yours may be different than mine.

Either way I don't think it should not run unless the indoor humidity is rather high already. You may have a bad wire or connection.

[Tony Hwang]

Hi, Maybe the 'stat is located in wrong place? Mine is on the living room wall next to thermostat. Tony Tony

[toller]

The unit I got last year is completely different than the one it replaced. First thing to do is check your owners manual. Second thing is to contact Aprilair. Third thing is to repost here, with more information on what you have.

[Buck Turgidson]

It is model number 560, as shown here. They have a humidistat that looks like mine for $50. I'd guess I need to research it more to see if is working properly.

[trader4]

I have an Aprilaire that is the powered model. The humidstat goes on the cold air return plenum. There is also a temp sensor that goes outside. It's function is to reduce the humidity as the temp decreases outside. From the behavior sited, it sounds like the humidistat is bad. If it's set just short of the point where it would turn on, then with the heating system running regularly, it should come on before too long. Sounds like its broken and you essentially have just an on/off switch.

[Tony Hwang]

Hi, If the 'stat is mounted on the cold air return duct, I don't think it's measuring humidity of your living space, like your living room or hallway. Wouldn't it be common sense? Actually RH is function of DEW point which relates to temperature and moisture in the air. We are not measuring absolute humidity, we're measuring RH in this case. Tony

[Alice Beach]

Sorrr Toney, but I have to intergect. I think you have good intentions, but, not a clue as to pyhsics. Dew point has to do with the saturation point compaired to temperature, not relative humidity. Relative humidity is just that...the relatioship of dry air molecules and wet air molecules, absolute humidity has to do with the amount or wet air molecules per pound of atmosphere. Again your intentions are noble, but, you need to understand physics before you quote any!!!!! Lesson..........Dew point is the point at which saturation is reached and the temperature corisponds to allow a change of state from vapor to liquid...or...sublimation...look it up. A can of soda on a hot day causes condensation on the surface between the two temperatures allowing vapor ( water ) to change state to a liquid. The question was one of Enthalpy, ever heard of that? Before you respond do some homework and in particular the " Mollier " diagram. And do not confuse Ethalpy with Entropy...there will be a test...lol No offence intended, it is just that those that think they understand HVAC trade, dont have a clue as to the true natureof physics, or the laws of thermal dynamics. Example.....If you think you do know these things..name, Charles, doyels, and Boltons laws or pressure, temperature and volume, ......name them and I willl then be impressed

[Tony Hwang]

Hi, Yep, I slipped my mouth there. Should read DEW point is function of temp and mositure. PV/T=P'V'/T'? Is that Doyels? D should read B? Tony

[trader4]

And exactly how you measure humidity doesn't explain the basic fact that the problem humidistat is not responding at all. The OP clearly stated that he set it just short of the point that would make it come on immeadiately. In a house where it's cold enough outside that the heating system is running frequently, the humidifier should then come on soon thereafter and start running occasionally to keep the humidity up. His humidistat only turns it either on continuosly or off, depending on where he sets it. Definitely sounds like it's failed and simple to replace.

[Buck Turgidson]

Thanks for reading carefully!

[Stormin Mormon]

As a heating and AC guy, I've installed more than several Aprilaire humidifier. Sounds like you've got a bad humidistat. Yes, it's supposed to be in the cold return side. Yes, some of them have a sensor that goes outdoors.

Yes, replace the humidistat.

[Tekkie]

Stumped Moron posted for all of us....

I guess i will leave this alone because nobody can get hurt or killed by taking his advice; however wrong it may be...

[Alice Beach]

Hi Tony, actually each man looked at the corrisponding change from one of the three, alladding up to the fact that if one is altered that a change occurs in one of the others. It is not a simple equation of one divided by the other, rather a ratio of what changes when one is raised or lowered. I am assuming you are a hvac tech, and if so, I applaud you. Most techs are not concerned with how things work, just what to do. Here is another test....What law is this....................The electromagnetive force is dirrectly proportional to the current flow and inversly proportional to the resistance?? Give an example of where this would apply in our field. I am not trying to show any superiority here, I am actually excited to find another tech interested in the physics of what our field is about.

[trader4]

What the hell are you implying is wrong? The Aprilaire modes do have a humidistat thats mounted in the return and some models also have an outside temp sensor. I know, because I have one and can also read an installation manual.

[Bob]

Trader I don't think Alice knows what he's talking about. He's just trying to impress people with something he literally knows nothing about, but thinks he does. I have an Aprilaire 600 and am well satisfied with it.

[Alice Beach]

I believe everyone is entitled to their opinion, but do you comprehend what you read?? First the statement I dont know what I am talking about......can you tell me where I am wrong with any of my statements on physics or are you just spouting off. There is nothing I have said about the laws of physics that you cannot look up. Care to write back and prove me wrong?? Not just with accusations but facts? Second if you are comprehending what you read, you would realize that I am not addressing the april-air issue, I am conversing with another tech that is in the minority and one that should be sought after for his skills and desire to be a true trouble-shooter. I hope this does not fall into the catigory that your response does, rather explain that a couple of knowledge-able techs are having a conversation. Again if I am wrong prove it, dont just spout that I am, any adiot can do that.

[Michael Baugh]

You didn't mention the answer to the Alice question. Three letters, starts with "O". Include application.

[Stormin Mormon]

Who are you talking to?

[Duane Bozarth]

...

You might get more respect if you did a spell-check, Alice...

Even giving you the occasional typo, your spelling and grammar are atrocious...

interject compared corresponds offense Doyle it's "thermodynamics" not "thermal dynamics"

And, there's a definite relationship between dewpoint, temperature (wet and dry), and relative humidity...it's how it's measured...the other is correct, albeit not very precisely/well stated. (That is, it's in the neighborhood, but nobody from CalTech is going to be calling soon...).