Musings of an Energy Nerd

Understanding Dew Point

Posted on July 13, 2018 by Martin Holladay

The dew point is a temperature. In my article on the psychrometric chart, I defined dew point as “the temperature at which moisture in the air begins to condense on hard surfaces.” Dew point can be measured or calculated for a specific point in time at a particular location, indoors or outdoors. No matter where it’s measured, the dew point can never be higher than the air temperature.

Here are a few other definitions for “dew point”:

  • The dew point is the temperature to which air must be cooled to become saturated with water vapor.

Ducted Air-Source Heat Pumps from American Manufacturers

Posted on July 6, 2018 by Martin Holladay

Mitsubishi and Fujitsu sell air-source heat pumps (ductless minisplits and ducted minisplits) that work well in cold climates. Many readers report that these appliances are providing dependable space heating in climates as cold as Minnesota, Vermont, Maine, and Quebec, where temperatures drop to -20°F or colder.

Traditionally, U.S. manufacturers of air-source heat pumps have favored ducted units over ductless units. Most air-source heat pumps sold by Bryant, Carrier, Lennox, and Trane, for example, are designed to be hooked up to forced-air ductwork, just like a typical furnace.

Fasteners for Concrete and Brick

Posted on June 29, 2018 by Martin Holladay

Builders who install rigid foam insulation need to know what type of fasteners to use for a variety of substrates. One challenging situation involves installing rigid foam or furring strips over concrete, as might happen when rigid foam is installed on the interior of a basement wall. But even builders who are familiar with fastening methods for concrete might wonder if the same techniques are appropriate for brick walls.

Using a Dimple Mat to Keep a Basement Wall Dry

Posted on June 22, 2018 by Martin Holladay

Homeowners with problematic basements often post questions on They generally complain that their basements are damp, and that basement moisture problems aren’t easy to fix.

Solutions to damp basement problems are only indirectly connected to the topic of green building. In recent years, however, green builders — that is, builders who focus on energy efficiency — have become experts on moisture problems in buildings, in part because insulation problems are intimately tied to moisture problems.

Where Can I Find Good Advice?

Posted on June 15, 2018 by Martin Holladay

Donald Wulfinghoff is an energy consultant who works in Maryland. In 2013, he published Super House, a 700-page book that explains how an ordinary person without architectural training can design a superinsulated home that (he claims) will use only 10% to 20% as much energy for heating and cooling as a conventional home.

Growing Marijuana Indoors is an Environmental Disaster

Posted on June 8, 2018 by Martin Holladay

Many Americans live in areas of the country where the local utility sponsors energy efficiency programs — for example, one that offers homeowners free energy audits. In addition to offering this type of residential efficiency program, many utilities have also developed energy efficiency programs to help commercial customers, including retailers and manufacturers.

What Windows Should I Buy?

Posted on June 1, 2018 by Martin Holladay

Readers often post a simple question on our Q&A page: “What brand of window should I buy?” For an editor, it’s an exasperating question, because it’s unanswerable. The answer depends on a host of factors, including the buyer’s geographical location, performance expectations, budget, and personal sense of aesthetics.

Rather than attempting to answer the question, I decided to interview fourteen designers and builders of high-performance homes. I asked them, “What brand of window did you specify on recent high-performance projects — and why?”

The California Model

Posted on May 25, 2018 by Martin Holladay

Here in the U.S., it’s hard to generalize about residential new construction standards. In parts of Massachusetts and California, many residential builders pay close attention to air sealing details, and the use of blower doors is common. Meanwhile, in Kansas and Wyoming, few builders pay much attention to air sealing.

These disparities are due to a variety of factors. But the most important explanation concerns differences in regulations. Massachusetts and California have stricter building codes, and do a better job of enforcing those codes, than Kansas and Wyoming.

Ensuring Fresh Air in Bedrooms

Posted on May 18, 2018 by Martin Holladay

Green builders try to make their homes as tight as possible. To ensure good indoor air quality, green building programs (and many residential building codes) require new homes to have a mechanical ventilation system.

Building a Passive House for $163 per Square Foot

Posted on May 11, 2018 by Martin Holladay

A family in Wakefield, Rhode Island, recently moved into a new 1,840-square-foot Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. with three bedrooms and two bathrooms. If you exclude the cost of the lot, the architectural fees, and the cost of getting the house certified by PHIUS, the construction cost was $300,420, or $163 per square foot (if you measure the area of the house on the exterior).

The members of the team that built the house include Brad and Jordan Hevenor, the homeowners; Steve Baczek, the architect; and Stephen DeMetrick, the builder.

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