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This is my 3rd Aprilaire 600 and they were all worth every penny. (The 600 used to be called the 600A, now both are automatic and the 600's electronics are slightly updated.) The 600 can be switched to manual mode, if desired.
My first unit was in my last house and was run for 2 years with no issues, then we moved. I just installed 2 in my current house (since I have 2 furnaces, 1 for each floor). I set it to humidity level #5 out of 7, which sets the relative humidity to 35% when the outdoor temperature is about 20 degrees F (details in the manual). The unit automatically turns on when the furnace is running and there is a call for more humidity. The unit can turn on your furnace blower in order to add humidity even when the furnace is not running, but I didn't want that option, so I didn't wire it in. If you do wire it in, there is a switch on the control unit so that you can turn it on or off.
Pros
* It's automatic and comes with an outdoor temperature sensor. This allows the unit to automatically adjust the humidity level so that you don't get condensation on your windows (condensation and the associated mold growth are why some home inspectors do not recommend humidifiers.)
* For us, it reduces nose bleeds and sinus infections.
* No standing water for mold to grow in. No individual room units to clean and refill.
* Works great, turn it on as the weather starts to get cold (also turn on the water to it and turn the lever to open the built in damper) and turn it off as the weather warms up.
* Low maintenance: Replace the water panel 1 time per year
* Low repair costs: There's no fan or extraneous parts. The only moving part is the valve that turns on and off the water. The value is quick and cheap to replace if it ever builds up enough sediment or mineralization to impede function.
* Low upkeep: The manual says to replace the water distribution tray and valve solenoid every ~5 years. All the parts are easy to access and relatively cheap. After 2 years my original water distribution tray showed no wear and I don't think it will really need to be replaced.
* Integrates with the electrical power in your furnace, so there's no extra wiring (assuming your furnace is new enough to have the jumpers.)
* Completely silent.
* Uses almost no electricity
* I did not notice a decrease in air flow coming out of vents throughout the house.
* Easy to install if you are handy. Our local Heating guys charge about $450 to install these and it only takes them 2 hours. I did it myself in about 4-6 hours. All the tools you really need are sheet metal snips, a good drill to put in sheet metal screws, a wrench for tightening plumbing connections, wire strippers, and ideally a 3/4" metal drill bit to install the electronic control. Installation instructions are included in the box, including wiring instructions. The instructions aren't idiot proof, but they're easy to follow for a handy person.
Cons
* Some water is wasted as unevaporated water does drain out the bottom. While I don't want water wasted, I actually think this is a preferable design. I don't want to waste electricity heating the water to create steam and I don't want a tray of standing water for mold or bacteria to grow in (the 400 model has a tray of standing water and no drain, but is otherwise the same as the 600.) I haven't noticed a change in my water bill since installing these units.
* A drain is required. I directed mine into my air conditioner's condensation drain which feeds to the sump pump. No problem. It it's a problem for you, try the 400 model.
Function
The unit works by taking air that has been heated by your furnace and passes it through a panel that has a small amount of water running across it. The water panel looks a bit like a radiator. The water on the panel evaporates into the hot air and gets distributed through your existing ductwork. That's it, nothing fancy. Note that, just like any humidifier, the unit is more efficient if you connect it to hot water rather than cold.
If you decide to install it yourself and go against the recommendation to have a professional do it, you'll also need the following:
#8 sheet metal screws
1/4" copper water line
1/2" ID clear vinyl tubing for drain
Clamp to attach the vinyl drain tubing to the humidifier
Small wire nuts
6" start collar for bypass connection
6" 90 degree elbow(s) for bypass connection
6" pipe for bypass connection
18-2 thermostat wire (a few feet of 18-5 may be helpful to go between the humidifier and your furnace, but 18-2 will work there as well)
Depending on your furnace, 2 quick disconnect electrical plugs may be needed to connect the included transformer to your furnace's power.
If furnace circuit board does not include humidifier accessory terminals an Aprilaire #50 Current Sensing Relay will be needed.
Optional Duct tape (don't use fabric tape, UL rated foil backed tape will last much longer and won't burn) or mastic will improve heating efficiency.
Optional you may want to feed the vinyl drain tubing inside a 3/4" PVC drain to make sure if doesn't get damaged or knocked out of your drain.
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Aprilaire Model 600 Automatic Whole-house Bypass Humidifier with Digital ControlThis is a highly sophisticated humidifier. I consider myself to be a fairly handy homeowner but after receiving the item and reading the directions I opted to pay a professional for the install. I am glad that I did. I had estimates in my area to do the install between $250 and $350 over the cost of the unit.
Everything on this unit is automatic. A hard wire runs outside of the house to monitor the outside air temperature.
The only question that I had before I bought the unit was weather the 3 gallons per hour of water ran 24/7 or not. The answer is that it does not. A solenoid only lets the water run when the unit needs to add humidity.
I am more satisfied with this product than I expected to be.
Best Deals for Aprilaire Humidifier, 24V Whole House Humidifier w/ Auto Digital
It's a great product and it works extremely well when set to full automatic. The outdoor temperature sensor needs to be installed for automatic mode for proper relative humidity and to avoid window condensation. Yeah it takes some time to install it properly but well worth it. When it's set to automatic it will actually kick on your blower periodically even without a call for heat to get an accurate check of the humidity levels and stay on if they are low. The automatic mode helps tremendously after the heat runs and it needs to stay on for a bit to keep the levels accurate. I also found this setup to be useful in reducing cold spots in the house and to help maintain even temperatures kind of like a 2-stage furnace would. With a flip of a switch it can be set to manual and will only run if there is a call for heat and humidity is required. If you're going to spend the time to install one of these, I wouldn't settle for a unit that is not automatic. The 24vac transformer that was sent with the unit was pretty cheap; I tried to loosen one of the terminals and it broke the lead. Not worth a phone call so I just picked up one at the hardware store for $13. If you plan on using this for automatic purposes, then the transformer should be powered with constant power. I ran power down from the furnace power switch to the blower compartment where I mounted the transformer. That's also nice because when you shut down the furnace via the switch it also shuts down the humidifier and adds protection with the onboard furnace fuse. You will want to wire the transformer at the switch and not from any wires or furnace electronics after the switch (excluding a designed HUM accessory power lead). Like many others my furnace's Honeywell circuit board is equipped with a HUM accessory power lead and on my unit it is 120V so don't think you can bypass the use of a transformer if that's the case. But if your board is similar to mine the HUM power lead will only work if you plan on using it in manual mode as it's only powered when there is a call for heat; it is not powered when there is only a call for the blower or no call at all. Obviously the unit will be more efficient when supplied with heated air; as will be the case most of the time. But there are several studies that show a sufficient amount of humidity will be applied by just the blower moving ambient air through the unit. The manual does state that when set to automatic mode then the unit should be supplied with hot water and in general that is a good practice for the MOST efficient way to evaporate water and help keep the impurities from building up over time. But I couldn't justify the usage of energy that it takes to make that water hot and watch it go down the drain. Some studies show that the benefit is insignificant in supplying hot water over cold water. It's going to be up to you but I couldn't do it and the unit still works very well when supplied with cold water. Hope this helps some of you out in the decision process and I posted a few pictures of the install.
Honest reviews on Aprilaire Humidifier, 24V Whole House Humidifier w/ Auto Digital
So like others mentioned... the install guide(s) are a bit crude. Install took me just over 3hrs to do. I piggy backed of the 24v supply already there for the furnace. Used the hot water line for best performance. The tough spots were tin snipping the openings (now i have increadible grip strength) and fitting the 6" flex duct hose (must be a trick to it i don't know) to the unit and the flange. Make sure your sheet metal screws are long enough as mounting holes on the unit are raised. I used an earlier review which had a check list of supplies needed for this project and for once didn't have to make two trips to the hardware store (thanks!).
Some tips: To get the unit to work without the temp sensor in place make sure you select manual on the Digital controller (otherwise water won't flow and error message will show). Make sure you get enough wire (@ $.23 a foot better to have extra then to waste gas and time going back). Finally make sure you are at least 6" upstream from your unit with the Control mounting otherwise you will get higher moisture readings.
I was able to turn down the temp in the house 2 degrees and still felt it was too hot in the house (2,500sqft). I am sure i will be getting returns on this for a long time not to mention how pleasant the house feels.
Aprilaire Model 600 Automatic Whole-house Bypass Humidifier with Digital Control
Find helpful customer reviews and review ratings for Aprilaire Humidifier, 24V Whole House Humidifier w/ Auto Digital
The humidity hasn't been low enough yet to actually run this yet so I can't comment on its effectiveness (will update review later). However, installation was fairly easy if you are somewhat handy. Wiring in to furnace was a breeze with included wiring diagram. I mounted the 24VAC transformer in a junction box on the side of the furnace. I installed the unit on the cold air return due to concerns raised in other reviews about water dripping down in to the furnace. I opted to not use the saddle valve and chop my hot water pipe and solder in a T with a ball valve instead (not a fan of saddle valves).
