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I am in the process of choosing an air handler to use only for AC. I plan to keep radiant heat. However, in the winter, I would like to use the AC system to blow humidified air to compensate for the dryness of air caused by radiators in lieu of having a standalone humidifier in each room.

Is this option even possible? I was thinking that my air handler would have water supply piped to it and then a mechanism to produce mist out of it and then blow it throughout the ductwork. But I am not sure if this even exists and whether it could cause harmful condensation in the ductwork.

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2 Answers 2

Whole house humidifiers exist, and could be wired to work in your situation. This would require the air handler blower to run during the winter, and humidity level detection might be a challenge.

Typically the humidifier is installed on the return ducting of the air handler, and a bypass duct is connected to allow the humid air to bypass the furnace/air handler. A humidistat is also installed on the return air ducting, which allows the humidifier to activate based on the humidity in the air coming from the house. Since you won't want the air handler to run constantly, you'll have to figure a way to passively detect the humidity level throughout the house. You'll then activate the blower, and the humidifier based on that.

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As stated in the other answer, yes whole house humidifiers do exist, and work great in many systems. However, when using one without a furnace, or an air handler that does not contain a hot water fan coil will be quite inefficient at adding humidity and water consumption. Warm air can hold more water vapor than cold air. When air temperature rises so does the temperature of water vapor. When the temperatures raise there is a higher saturation of vapor pressure. Basically, when blowing cold air through a flow-through humidifier, there will be much less water vaporization, and thus much less humidity being added to the air for the same volume of water running through the unit.

Now, you were wondering about misters as well. Misters do exist and are on the market. I have a few suppliers that carry duct-mounted misting systems. My experience with them however is that they will only work efficiently with a Forced Warm Air system. It would also require a humidistat to control the humidity level, and some sort of "sail" or "pressure" switch installed to ensure that the humidifier can only run when the blower on the air handler is in operation.

The type of humidifier I would recommend for your application would be a Steam Humidifier. From my personal experience, the Aprilaire Model 800 Residential Steam Humidifier is good. They are easy to service, and I have never had any major issues with the units. With all steam humidifiers, much like misting systems, there is a humidistat to control the humidity level, and some sort of "sail" or "pressure" switch installed to ensure that the humidifier can only run when the blower on the air handler is in operation. Now it is imperative to fully understand the quality and hardness of the water that will be used on the steam humidifier. Water quality and water hardness can vary greatly from home to home, and even between two homes on the same street. Proper filtration is critical for the operation of any steam humidifier. Failure to address water quality can potentially lead to drastically increased maintenance requirements and premature failure of the steam humidifier and its components. Be sure to complete the following procedure well in advance of installation to ensure any additional costs are documented and understood. Water test kits are available and do come with some steam humidifiers on the market. I would recommend the Honeywell water hardness test kit for ease of use. More information about this and on steam humidifiers can be found in the Honeywell TrueSTEAM Humidifier Manual. Depending on just how hard your water is at your house, you would either need a Phosphate filter for mild hardness, Reverse Osmosis Filter, or a whole home water softening system.

Even with the added components, and the addition of the water filtration system on many applications of the steam humidifier, I would still highly recommend one for your specific system. In most cases, even with severe water hardness, the unit can operate normally with just the RO filter, or even in many cases most are installed with just the phosphate filter. However still take a water hardness test regardless. Make sure that all equipment is installed by a Certified HVAC technician, and they have experience installing and servicing steam humidifiers.

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