What an R-61 wall actually does to a January heating bill in Cheshire County

Keene runs past 7,000 heating degree days a year. Here is what that means in oil, propane and cord wood when the wall changes.

Every January someone asks us the same question in a slightly different way: what do I actually save? Not the marketing number — the number on the bill. It is a fair question and it deserves arithmetic rather than adjectives.

Start with the load, not the wall

Southwestern New Hampshire runs roughly 7,000 to 7,600 heating degree days depending on where you sit in the valley and how high you are. A 2,000 square foot code-minimum house in that climate typically wants somewhere between 750 and 950 gallons of oil a year, or the propane and cordwood equivalent. That is the baseline the conversation should start from, because a percentage saving means nothing until you know what it is a percentage of.

Where a code wall leaks

A 2×6 wall at 16 inches on centre is nominally R-21 in the cavity. It is not R-21 as built. Every stud is a thermal bridge, and once you count studs, plates, headers and corners, the whole-wall value lands closer to R-15 or R-16. Add the air leakage that comes with sheathing seams, and a meaningful share of your heating season is spent warming the outdoors.

What changes with a thermally broken panel

A ThermaSteel exterior panel is 5.5 or 7.5 inches thick and performs at an effective R-51 to R-61 — effective, meaning after the framing is accounted for, because the steel studs are broken from the exterior face rather than running straight through the assembly. There is no cavity to fill badly, no gap for the insulation to settle away from, and the panel is its own air and vapour control layer.

The practical result on a well-built house in this region is a heating energy reduction on the order of 70 to 75%. On that 900-gallon baseline, you are looking at something in the region of 225 to 270 gallons. At a delivered price that moves between two and four dollars, that is a swing of $1,800 to $2,700 a year, every year, for as long as the house stands.

The part people miss

The upfront equipment saving is often the more interesting number. When the design heat loss drops by that much, the boiler, furnace or heat pump you need drops with it — commonly by about half. A smaller cold-climate heat pump system installed at the start is thousands of dollars that never leaves your account, and it is the reason the panel premium is smaller in practice than it looks on a materials quote.

What it feels like

Numbers aside: a continuous, air-tight, thermally broken shell in January is a house without cold walls and without the draught you feel at the base of a stud bay. Rooms stay within a degree or two of one another. Setback recovery is fast because the shell holds what you put into it.

If you want this run against your own plans rather than a generic 2,000 square foot house, send them over. We will do the take-off and give you both numbers — what the package costs and what the wall saves.