Green Design

Published on May 18th, 2008 | by Chris Schille


Heating Your Home: Forced Air

DuctsAuthor’s note: the following article on home heating is the third in an eight-part series. This article addresses climate conditions found in the San Francisco Bay Area, but may have applicability elsewhere.

Forced air systems are the most common heating systems in California and are used in most new construction elsewhere. They have two big advantages: they are cheap to install, and they provide heat at a moment’s notice. Having “instant-on” heat is vital for intermittent use spaces like ski cabins. Otherwise, forced air is the least energy efficient and least comfortable way of heating a typical home. Why?

Ventilation and Heat Loss

For the health and well-being of its occupants, a home must exhaust stale air and refresh it with new air drawn from outdoors. Forced air systems heat and blow this air, via ducts, throughout your house. Since new air is continually entering and leaving, you are heating the outdoors.

There are ventilation systems specifically designed to make HVAC less wasteful. Heat Recovery Ventilators (HRVs) transfer heat from warm outgoing air to cold incoming air. (A comparable device called an Energy Recovery Ventilator can cool incoming hot air in hot-humid climates.) Running for some fraction of each hour, HRV fans typically exchange enough air with the outdoors to keep inside air fresh. However, HRV is rarely considered cost effective in our climate.

Even in the most air-tight houses, air is lost via unsealed combustion devices, bath or range exhaust fans, and the opening and closing of doors.

Ducts, Mold, Mildew and Rot

The ducting that moves the heated or cooled air is a network of hidden spaces that can collect and redistribute debris and moisture. When the heat cycles off, warm air cools and condenses inside the ducts, forming liquid water. The moist, protected environment is an ideal space for mold and mildew to breed. Broadcasting any dust, mold, mildew or pathogens growing in the duct work, forced air is often at the heart of Sick Building Syndrome.

Ducts also leak. PG&E estimates that the ducts in a typical home leak as much as 30% of the air they move. This warm, moist air can escape into an unconditioned space (for example, an unheated attic or crawlspace), cool, condense, and deposit water where you don’t want it and can’t see it, like your roof or floor framing. Subjected to enough regular wetting, this wood rots. When heated or cooled air escapes into unconditioned space, it heats or cools the outdoors, not the house.

Dry Sinuses, Skin and Eyes

Many consider forced air inherently uncomfortable. Since the blown air needed to heat the rest of the air in a room must be substantially warmer than the ambient air temperature, many people find that it dries their eyes, skin and sinuses.

As a homeowner, you have alternatives to forced air. The next article explains thermal mass and radiant heat.

Previous Heating Your Home Articles:

Photo credit: pixelviz via Flickr

Hancom: ThinkFree Mobile Viewer Is the Default Office App in Google Nexus S Smartphones.

Health & Beauty Close-Up January 6, 2011 Hancom Inc. said that the company has been working with Samsung Electronics Co. to embed ThinkFree Mobile Viewer, the mobile version of its office application, on Nexus S smartphones, the world’s first Android 2.3 (Gingerbread) device. go to website nexus s review

In a release, the Company said that it hopes this milestone will help introduce Android users to the high quality and performance of ThinkFree Mobile Viewer.

ThinkFree Mobile is included with the latest Android-based devices available today including Galaxy S and Galaxy Tab. Being part of the new Nexus S helps position the app as the global mobile office standard. see here nexus s review

ThinkFree Mobile with editing capabilities is available for purchase through Android Market.

ThinkFree, Inc. is a developer of ubiquitous documentation platforms to offer boundless office productivity environments.

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About the Author

Chris Schille discovered his true passions early in life when his parents moved to a piece of bare land in Humboldt County, California. There they built their own passive solar home, planted a huge organic garden, and joined a community striving for self-sufficiency. It was there that Chris developed a life-long love for the natural world and rural life. Chris holds degrees in mechanical engineering and computer science. After a ten-year stint in software, he left to design and build his own passive solar home (in Humboldt). A love for all aspects of building, and concern for its environmental costs, led him to start his own residential building business, Rustic Precision. He lives with his wife and daughter in Cupertino, California.

6 Responses to Heating Your Home: Forced Air

  1. kym says:

    I like the simple, clear explanation of something I had felt all along–forced air makes me feel like I have a cold.

  2. kym says:

    I like the simple, clear explanation of something I had felt all along–forced air makes me feel like I have a cold.

  3. AC Doctor says:

    A high efficiency heating and cooling system can not only help save money on heating bills, but can also improve the air you breathe.

  4. AC Doctor says:

    A high efficiency heating and cooling system can not only help save money on heating bills, but can also improve the air you breathe.

  5. Trey Hopson says:

    List down all of the possible options that you can avail, then take note of each item’s pros and cons. Choosing the right ventilation and heating system for your house should be carefully done, because what’s at stake here is the comfort of the people living in your house. It’s good that this article gave some pros and cons on one of the available heating options out there.

  6. I saw this diagram about where does your air current come and go. Apparently, you lose hot/cold indoor temperature the most, because of improper insulations in your attic and ceiling. Paying attention to that will make sure you’ll get the most out of your heater/air conditioning unit.

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