Central Humidifier with Hydronic Heat

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Old 01-16-19, 01:49 PM
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Central Humidifier with Hydronic Heat

My house has hot-water heat. Unlike a forced-air furnace with ducts, there is no convenient way to add a humidifier for the whole house. I've gotten by with a couple of portable humidifier units, but they can be messy and take time for daily manual refilling.

I've recently installed an Aprilaire Model 350 humidifier, which seems to be the answer, at least for my situation. You can Google for detailed info. There may be comparable units from other manufacturers, but I didn't uncover any. Supplyhouse.com stocks the Aprilaire unit, but there may be other, less-expensive sources

Briefly: the unit hangs between ceiling joists in the basement. You need to add a 7" flexible duct and cut in a floor register in the first floor. Also, a 1/4" copper tubing for makeup water from a hot-water supply (DHW - a hot-water boiler is too hot), and a 1/2" drain hose going to a floor drain. The unit comes with a 24-V humidistat and has a built-in fan and solenoid valve.
 
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Old 01-16-19, 03:58 PM
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You must have excessive cold air infiltration as typically a hydronic system doesn't require additional humidification. It's not like a furnace where the furnace dries out the delivered air.
 
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Old 01-16-19, 04:44 PM
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Pete: Those with hydronic heat that do not suffer from too-low indoor humidity, will quickly see that a humidifier is not necessary.
 
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Old 01-17-19, 03:13 AM
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It is an "old wives tail" that homes with hot water heat do not suffer from low humidity problems as do homes with forced air heat. People have claimed for years that the forced air furnaces burn, reduce, or what ever term you want to use, the humidity in the air. I say B.S. All homes suffer the same consequences of low humidity when the air in the home is heated by any source.. Hot water heating and forced warm air heating affect the relative humidity exactly the same. Relative humidity is the amount of water vapor in a quantity of air at a given temperature expressed as a % of the total that can be held. Raising the temperature of that same quantity of air will allow that air to be able to hold more water vapor thus reducing the % of the total. If you can show that I am wrong, please let me know. Just make sure that your rebuttal is scientifically correct..When I worked for a company in the residential HVAC we installed many humidifiers in homes with hot water heat due to low humidity. It looks like "Gilmorrie" started a thread then he offered a rebuttal to his thread. Am I wrong
 
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Old 01-17-19, 02:34 PM
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Googling a psychrometric chart or an on-line psychrometric calculator will help quantify the process of indoor winter air becoming dry. A few hours ago, our outdoor air was 28 deg F, 95% relative humidity, and absolute humidity of 21 (don't worry about the units of AH). When that outside air infiltrates into our house, the AH doesn't change, but the temp is increased to 72 deg F, and the RH drops to 18% - uncomfortably dry.

Infiltration is usually quoted in air changes per hour, which is mainly dependent upon the tightness of construction and the size and shape of the house. The precise formulas are complicated, but ASHRAE has published simplified tables. For my house, the typical "default" infiltration rate is 0.37 air changes per hour. (This rate applies for whatever the type of heating - hydronic, steam, forced warm air, electric, etc.)
 
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Old 01-17-19, 02:40 PM
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Gilmorrie did not assert that hot air systems need humidifiers more than hydronic systems. He only said (correctly) that it is easier to add a whole house humidfier to a house with a hot air system and/or central air conditioning compared with only a hydronic system.

An open floor plan and/or ceiling fans may allow greater coverage from fewer humidifier units.
 
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Old 01-17-19, 03:24 PM
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The 350 is a good unit. All I use is Aprilaire products. The only other unit that you may have considered is the sister to your unit..... the 360.... that is wall mounted.
 
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