Winter Humidity Issues

Dated: 02/11/2014

Views: 1837

People ask if a gas or oil furnace dries out the air in a home and makes a humidifier necessary.  People who work in the HVAC industry can get confused by this quest, so let's take a look at the issue.  Air in a home can get dry during the winter. You notice the difference in your skin, the amount of static in the air (in my case the fur on my cat Darla stands straight up!) cracks magically appear in your woodwork and trim.

The air in a home can get dry in winter. You can end up going through a lot of moisturizer, as well as sneaking up on people and giving them a shock.
What does a furnace do? A furnace heats the air. It raises the temperature of the air in your home so you don't freeze. But as you go from summer to fall to winter, most people actually lower the temperature they keep the house at.
Your heating systems heat by burning natural gas or fuel oil. There, there are two kinds of gas furnaces or boilers; atmospheric and sealed combustion (condensing) furnaces or boilers. In sealed units, most draw air from outside the structure, some units give the installer the option to use inside air; however why anyone would want to spend the money for this equipment and not fully utilize this option confuses me. Another big user of combustion air is an atmospheric gas water heater. Atmospheric furnaces and water heaters draw combustion air from inside the home.  Sealed units typically are above 90% efficiency, you can tell by the PVC flue and intake air pipes. Most of the energy consumed is converted to heat, leaving only water vapor. Atmospheric furnaces that are located inside the conditioned space (closet, basement or utility room) further deplete the available moisture in the home by using this air for combustion.  The only time this does not occur with this equipment is if it is located in an attic or crawl space.
During the winter, the outdoor humidity is typically between 20% and 30%, compared to the typical northeast summer humidity of around 70% to 80%. With atmospheric equipment, you are drawing air and moisture from inside the structure. Inside furnaces have always had the option to enhance indoor air quality by adding filters and humidifiers. This presented an issue for homes that have their atmospheric furnaces in attics or crawl spaces. You could not install a humidifier on these units due to the possibility of these components (which require water and drains) freezing. Fortunately there have been humidifiers that have been recently developed that can be remotely mounted (as far as 20 feet away) inside the conditioned space.
People with boilers don’t have this option; they will still have to rely on portable humidifiers.
Most homes have significant air leakage, through windows, doors, leaking duct work and inefficient air sealing. Due to this, the dryer air that occurs outside during the winter has a means to leak or infiltrate into the home, making the humidification issue more noticeable. Also if there is significant leakage, it results in the heating equipment running longer consuming more energy and requiring more combustion air.
Your heating, cooking and clothes dryers all use air, and in the case of your furnace and clothes dryer, they intentionally exhaust air. Air has to have a way to get back in the structure. That’s why it’s important that in order to maintain good indoor air quality that sufficient make up air be provided. Sealed equipment helps to minimize this effect.
Older homes seem to be a bit better on allowing infiltration air and humidity to penetrate the home.  Unfortunately if there is too much infiltration air, run times on the equipment increase along with energy costs, newer homes have a different problem, modern construction techniques provide for a tighter home, which can lead to a lack of air or humidity in the home.
 Atmospheric furnaces will be getting harder to obtain, the trend is for the switch to higher efficiency condensing furnaces or boilers and tankless water heaters. This should have a dramatic effect on indoor air quality.

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