Rowhouse Heat: Walking the Line Between Mandates and Good Sense

By Mark Alan Hughes

A few years back, I helped lead a research project on improving energy efficiency in buildings for the U.S. Department of Energy. My team had a motto that I translated into Latin: “planto is imitabilis, planto is vilis, tunc planto is mandatum," which basically means “make it hipper, make it cheaper, then make it mandatory.”

Eventually, government has to draw a line and call some things mandatory. But rules need to bend, and sometimes they need exceptions to achieve the greater good.

On March 12, DOE published a proposed rule that would seek to raise the mandatory energy-efficiency standard for a residential furnace that can be sold nationwide. (Thanks to vigilant folks at the Philadelphia Gas Works for bringing this to my attention.) The current standard is 80 Annual Fuel Utilization Efficiency (AFUE) and this allows a homeowner to install a non-condensing furnace.  DOE is proposing to require a 92 AFUE, which is a much higher efficiency rating.

At that level of efficiency, the combustion exhaust now drifting up through Philadelphia’s thousands of rowhouses would no longer be hot enough to rise out of the chimney and would condense, or form drops of water, in the vent. The new rule would require condensing furnaces, which have additional venting requirements that add significant dollars to the cost of installation.

That’s a kick in the head for Philadelphia’s 400,000 rowhouses with their energy-efficient walls and small roof-to-area ratio. These very same factors constrain the use of condensing furnaces in rowhouses.

Non-condensing furnaces employ net-negative vent pressures and require masonry chimneys or metal vents that are installed vertically. These vertical chimneys exist in nearly all of Philadelphia’s rowhouses. Condensing furnaces employ positive net pressures, and use plastic, pressurized, gas-tight venting that is typically installed horizontally, requiring blowers to exhaust combustion products and condensate drains to operate properly.

Replacing a non-condensing furnace with a condensing furnace in a typical Philadelphia rowhouse will require a new venting system, including abandonment of the existing venting system, structural changes to accommodate a new venting system path, and relocation of the furnace to meet the code and installation requirements of the new condensing furnace system.

These additional costs are likely to delay the installation of higher efficiency non-condensing furnaces, extend the use of existing furnaces beyond their safe operating life, drive owners to switch to alternative heating systems that may well be less safe and/or less economical than non-condensing furnaces, or some combination of all of these outcomes.

In effect, the highly efficient rowhouse building type is being penalized with a mandate to use a technology that costs more in a rowhouse than a ranch house. DOE rules should acknowledge the advantages of the rowhouse building type while still requiring improvements when feasible.

One way to do this would be to treat condensing and non-condensing furnaces as two separate product classes, with different efficiency standards for each. A second way would be to provide a provision allowing non-condensing furnaces with optimal AFUE ratings in building types that meet threshold energy performance levels, such as rowhouses. The latter would recognize that a rowhouse with a less efficient non-condensing furnace still consumes less energy for heating than a free-standing home with a more efficient condensing furnace.

Total energy efficiency performance is the ultimate goal for these rules, and the public interest would be poorly served by creating a disadvantage for the rowhouse, one of the most efficient building types in the country.

DOE is accepting comments on the new rule until July 10. Comments may be submitted online here.

Image credit: Flickr/John Vosburgh's Elfreth's Alley 

Mark Alan Hughes is Faculty Director of the Kleinman Center for Energy Policy at Penn and was the founding Director of Sustainability for Philadelphia.