Central humidifiers.

Central humidifier installation, use, cleaning, connections, & building codes. Should a central humidifier be used at all on a heating system? Where would a central humidifier best be located?

How is water supply conducted to a humidifier? Should you pipe hot water to the central humidifier system? Central humidifier cleaning, maintenance, & health effects or risks.

Using a Central Humidifier Attached to a Heating Furnace

Question: how to connect hot water to a central humidifier

2018/01/11 Eric said:

I've added a humidifier to my furnace and would like to use hot water (recommended by manufacturer) from my hot water heater to supply water to the humidifier.

[Click to enlarge any image]

Can I screw a T-Valve into my water shutoff valve, add a new shutoff on the other end of the T-Valve, and use this to supply my humidifier without violating codes?

Correction: I meant to ask if I can screw a T-Valve onto my water heater drain valve on the bottom, not onto the water shutoff valve.

This question and answer were posted originally

at HEATING SYSTEMS

Reply: OPINION: this connection is not-recommended

Eric,

I do not think a T-valve would be the proper application for providing hot water to your system humidifier.

Typical T-valves such as the Mondeo T-valve I illustrate here, are ball-valves used to divert flow from a primary input source to one of two different destinations.

The ball of the T-valve is drilled straight through and then an intersecting drill opening is made at a 90 degree angle to the first passage.

Ball valves are intended to be used in the fully-open or fully closed position, though some suppliers describe using a T-valve to permit sending output to two destinations simultaneously - you'd see reduced flow rate to both of them compared with a straight ball valve or an L-valve.

More about T-valves and L-valves is at PLUMBING CONTROLS & VALVES

Also there could be a risk of pressure-loss and backflow of unsanitary water from the humidifier to the building water heater or plumbing system (though double check valves could mitigate that risk).

The simplest installation uses a saddle valve that punctures a hot water line (or in my OPINION better, a cold water line) and uses a small diameter flexible copper tube to conduct water to the humidifier. However many plumbing codes no longer permit these valves.

Instead, in my OPINON, it would make more sense to simply install a tee in the hot water supply piping (or in my OPINION better to cold water piping) and then connect a simple ball-valve or gate valve (to permit flow adjustment) in line with the outlet of the tee that will feed the humidifier.

Unless you are going to keep filling your humidifier manually, and unless your humidifier includes a water feed control in its design, you'd want a sanitary float control valve to admit water into the humidifier.

BOTTOM LINE: drop the whole idea of connecting hot water to the humidifier and I would reconsider using a central humidifier at all

Why do we express this opinion?

There might be a small improvement in the production of moisture being sent into your furnace supply plenum or supply air duct by using hot water, but that benefit is likely to be offset by the formation of mineral scale and crud that HVAC technicians find troublesome as scale fouls controls and moving parts and increases service cost.

OPINION: frankly I am not a fan of central humidifiers that feed water into a supply plenum over a furnace heat exchanger.

In over 40 years of building inspections I have seen that most of the central humidifiers I've seen installed were not maintained, were not working, and many of them had leaked into and caused costly, even dangerous damage to the furnace heat exchanger.

Central humidifiers also can serve as mold amplifiers and mold distributors in buildings. (Solomon 1976).

For those reasons I prefer point-of-use portable humidifiers such as in sleeping areas.

See also CENTRAL HUMIDIFIER LEAKS into DUCTWORK

Watch out: do not try feeding hot water from your water heater's drain valve. You will have chosen the worst place to feed hot water into a humidifier as you'll be draining sludge and scale from the bottom of the water heater.

Research on Using a Central Humidifier in Homes

Photo: a central humidifier attached to the supply air plenum of a home heating furnace, showing a rotating drum that is encrusted with scale and debris. It is common to find that homeowners do not clean nor maintain the central humidifier. [Click to enlarge any image]

• Mohan, Aparna K., Charles E. Feigley, and Caroline A. Macera. "Humidifier use in the home environment and its effects on respiratory health." Applied occupational and environmental hygiene 13, no. 11 (1998): 782-787.
  Abstract:
  
  This study sought to examine the association between household humidifier use and subsequent experiencing of adverse health symptoms.
  
  The analyses were based on a cross-sectional survey of 101 people residing in Chester County, South Carolina. Evaluation of the effect of exposure to different humidifier factors on the respiratory and general health of residents using humidifiers was achieved by univariate and multiple logistic regression analysis.
  
  People who cleaned their humidifiers less frequently were more likely to report untoward health symptoms than people who cleaned their humidifiers frequently.
  
  This relationship persisted even after controlling for the effects of potential confounding factors: age, gender, race, smoking, and educational status.
  
  Infrequent humidifier cleaners had significantly higher odds of reporting adverse health symptoms like headache (adjusted odds ratio = 17.1), eye irritation (adjusted odds ratio = 9.9), sore throat (adjusted odds ratio = 11.1), nose irritation (adjusted odds ratio = 10.9), and cough (adjusted odds ratio = 14.3) than frequent cleaners.
  
  Currently physicians and researchers have divided opinions about the benefits of humidifiers and vaporizers.
  
  While increased humidity during winter months may reduce the number of respiratory infections and problems an individual experiences, results of this study indicate that proper maintenance of the equipment is equally important for preventing health problems.
• Patterson, Roy, Jordan N. Fink, Wayne B. Miles, John E. Basich, Donald B. Schleuter, David G. Tinkelman, and Mary Roberts. "Hypersensitivity lung disease presumptively due to Cephalosporium in homes contaminated by sewage flooding or by himidifier water." Journal of Allergy and Clinical Immunology 68, no. 2 (1981): 128-132.
• Solomon, William R. "A volumetric study of winter fungus prevalence in the air of midwestern homes." Journal of Allergy and Clinical Immunology 57, no. 1 (1976): 46-55.
  Abstract:
  
  Volumetric recoveries of airborne, mesophilic microfungi were made during winter months at three specific points in 150 single-family dwellings in southeastern Michigan. Mean levels of total isolates/m3 comprised a range of from less than 10 to over 20,000, although concurrent outdoor levels never exceeded 230/m3.
  
  Form species of Penicillium, Aspergillus, Cladosporium, and Rhodotorula as well as non-pigmented yeasts were the types encountered most widely indoors.
  
  Certain homes showed high recoveries of other types, including Cephalosporium, Sporobolomyces, Verticillium, and Sporothrix form species.
  
  A positive association between indoor fungus prevalence and bedroom relative humidity was strongly suggested, and high levels were observed in well-humidified homes despite the presence of electrostatic air cleaners.
  
  The data indicate characteristic patterns of (winter) air spora in specific homes and suggest that humidifying devices may serve as dispersion sources in addition to their permissive role in facilitating fungus growth.

...

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