Musings of an Energy Nerd

Finally, a Right-Sized Furnace

Posted on March 2, 2018 by Martin Holladay

For years, builders of energy-efficient homes have been frustrated by the lack of low-load furnaces. An article I wrote in 2013 about this problem began with this question: “Why are the smallest available American furnaces rated at about 40,000 BtuBritish thermal unit, the amount of heat required to raise one pound of water (about a pint) one degree Fahrenheit in temperature—about the heat content of one wooden kitchen match. One Btu is equivalent to 0.293 watt-hours or 1,055 joules. /h?”

A 40,000 Btu/h furnace is likely to be more than twice the size of what is needed to heat a small energy-efficient home. Many homes in this category have a design heat load of only 12,000 or 15,000 Btu/h.

Looking Back at Insulating Advice from 1951

Posted on February 23, 2018 by Martin Holladay

Up until the mid-1950s, almost every American carpenter had heard of Audels Carpenters and Builders Guide. Even carpenters who didn’t own all four volumes of the book series had probably studied the Audels books at some point in their careers, or knew someone on the job site who had copies of the books.

In a way, the Audels Guide was the Fine Homebuilding of the 1930s and 1940s. It instructed beginners in the right way to do things; it upheld standards; and it promoted quality work.

Using a Bath Fan to Equalize Room Temperatures

Posted on February 16, 2018 by Martin Holladay

On Green Building Advisor, readers regularly ask questions about room-to-room temperature imbalances — the type of imbalances that may occur when a home has a point-source heater like a ductless minisplit or a wood stove. Here’s a typical question: “I’d like to install a bathroom fan to move air from a warm room to a cool room. Will this approach be enough to equalize the temperatures between the two rooms?”

Things You Do Not Need

Posted on February 9, 2018 by Martin Holladay

Houses are changing. Anyone buying a new home in 2018 expects the home to be quite different from one built in 1918, of course.

What “new features” is the typical buyer of a new home seeking out? It depends. Some buyers are looking for a foyer with a 20-foot ceiling and a master bathroom with a big Jacuzzi. Others, including the typical GBAGreenBuildingAdvisor.com reader, are looking for low energy bills and superior indoor air quality.

Condensation on Car Windshields

Posted on February 2, 2018 by Martin Holladay

A surprising number of people don’t understand the causes of condensation. If you ask a stranger on the sidewalk, “Does condensation happen when cold air encounters a warm surface, or when warm air encounters a cold surface?,” many people will shrug their shoulders.

Here’s an example of this type of confusion: When drivers see condensation on their windshield during the summer, they are often unsure of the best remedy. Should they turn on the heater or the air conditioner?

Let’s look at four different scenarios.

Brick Chimneys With Multiple Flues

Posted on January 26, 2018 by Martin Holladay

One of my first construction jobs in Vermont, back in the late 1970s, was at an architect-designed home with a massive brick chimney with four flues: one flue for the oil-fired boiler, and three flues for the home’s three wood stoves. The chimney worked fine — mostly because the house had so many air leaks that the wood stoves were never starved for combustion air.

Massive chimneys like the one I remember from that job are expensive to build, but they are often a source of pride for the owner. They provide interior thermal massHeavy, high-heat-capacity material that can absorb and store a significant amount of heat; used in passive solar heating to keep the house warm at night. ; they are durable; and they are handsome to behold.

All About Air Purifiers

Posted on January 19, 2018 by Martin Holladay

If you’re concerned about indoor air quality, you may have noticed ads for a type of appliance called a portable air purifier. Purchasers hope that these boxes will suck in dirty air and discharge clean air, but few homeowners know how these appliances operate.

In this article, I’ll try to answer a few basic questions about portable air purifiers:

  • How many kinds of portable air purifiers are on the market?
  • Do they work?
  • Who needs one?

Will Thick Cellulose Cause Your Ceiling to Sag?

Posted on January 12, 2018 by Martin Holladay

It’s fairly common for cold-climate builders to install a very thick layer of cellulose on an attic floor (that is, above the drywall ceiling of the floor below). Many green builders aim for a ceiling rated at R-60, R-70, or even R-100. When it comes installing cellulose, the usual advice is to “pile it on.”

Cellulose rated at R-60 is about 16 or 17 inches deep. Cellulose rated at R-100 is about 27 or 28 inches deep. That’s a lot of cellulose — so much, in fact, that some builders ask, “Is my drywall ceiling going to sag?”

Vermont Addresses the 20+5 Wall Problem — Sort Of

Posted on January 5, 2018 by Martin Holladay

Three years ago I wrote an article about a problematic recommendation in the 2012 building codes — namely, the “R-20+5” recommendation for walls in Climate Zones 6 through 8. This recommendation — actually, a prescriptive minimum R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. requirement for walls — gives code approval to walls with R-20 fiberglass batts and R-5 exterior rigid foam. (Image #2, below, shows the relevant code table.)

Climate Change Challenges the Human Imagination

Posted on December 29, 2017 by Martin Holladay

We live in strange times. It's clear that our politicians have been remarkably inept at addressing the climate change crisis. Scientists tell us that we have already injected so much carbon dioxide in the atmosphere that, especially in light of the ineptitude of political leadership, it is almost certainly too late for the human race to avoid environmental catastrophe.

In short, the chain of events we have set in motion is in all likelihood irreversible.

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