How many HERS points does swapping a standard dryer for a heat pump dryer typically pull?

Enough to outpull an R-20 to R-25 wall assembly upgrade on the multifamily project we modeled. The exact number depends on unit count, building geometry, and what the rest of the design already looks like. Heat pump dryers use roughly half the energy of a standard electric resistance dryer, and that efficiency delta lands directly in the HERS index.

Are heat pump dryers required under any Massachusetts energy code path?

Not currently as a hard requirement, but they are increasingly cost-effective on performance paths like the Specialized Stretch Code where HERS or ERI targets drive compliance. On tight-target projects, the appliance choice can move the index more than envelope upgrades that cost ten times as much.

Why does an appliance change beat a wall upgrade on a HERS index?

Two reasons. First, dryers are large electric end-uses in a multifamily unit, so a 50 percent efficiency gain on a large load is a bigger absolute reduction than a fractional improvement on heating load. Second, an envelope already past code minimum is in diminishing returns territory on additional insulation, while the appliance is moving from a less efficient baseline to a much more efficient option.

Should we still upgrade walls on multifamily projects?

Often, yes, but the order of operations matters. Cheap HERS points should be picked first, which on many projects means appliance specs, DHW efficiency, and air sealing before another R-5 of continuous insulation. Once those levers are pulled, envelope upgrades may be the next place to find compliance margin. The model decides the sequence on each project.

Why a Heat Pump Dryer Beats a Wall Upgrade on HERS

On a Massachusetts multifamily project, a heat pump dryer pulled more HERS points than upgrading the wall assembly from R-20 to R-25.

May 09, 2026

On a multifamily project in Massachusetts, we ran the HERS model expecting the wall assembly to carry the most weight in the score. It did not. Swapping a standard electric resistance dryer for a heat pump dryer recovered more HERS index points than upgrading the entire wall from R-20 to R-25. A single appliance line item beat a re-engineered building envelope. That is not how most teams think about chasing a tight HERS target, and it is exactly why we model appliance specs alongside the envelope.

The Real Comparison

The project is a multifamily building in Massachusetts running the HERS performance path. We were asked to identify the cheapest path to a tighter HERS index, and we tested two upgrades against each other.

The first option was a wall assembly upgrade. The baseline was R-20 cavity. The proposed upgrade was R-25, with the additional R-value coming from a thicker continuous insulation layer outside the sheathing. That change ripples through the wall thickness, the window jamb extension, and the cladding attachment detail.

The second option was an appliance spec change. The baseline was a standard electric resistance dryer in each unit. The proposed upgrade was a heat pump dryer in each unit. No structural change. No envelope detail revision. One line on the appliance schedule.

The heat pump dryer pulled more HERS index points than the R-20 to R-25 wall upgrade.

The HERS Math

The reason the appliance won is straightforward once you look at the energy load it represents. Standard electric resistance dryers are large end-uses in the HERS model. They draw heavy current for short cycles, and across a year on a multifamily building they account for a meaningful slice of the total electric energy. Heat pump dryers use roughly half the energy of a standard unit. That efficiency delta lands directly in the index.

The wall upgrade pulls in a different way. Going from R-20 to R-25 reduces conductive heat loss through the wall area, which reduces the modeled heating load. On a tight envelope already carrying continuous insulation and a low ACH50 target, the marginal improvement from another R-5 is small. Diminishing returns are real on insulation, and they are visible in the HERS output once the envelope is already past code minimum.

A small efficiency gain on a large load can outpull a small efficiency gain on a small load. The dryer is the large load on this comparison.

Why the Wall Upgrade Lost on Cost

The wall comparison is not just a HERS question, it is a cost question, and the appliance route wins on both axes for a tight-HERS project.

Upgrading the wall from R-20 to R-25 ripples beyond the insulation line item. The additional thickness pushes the window detail outward, which means longer jamb extensions, modified flashing details, and a different cladding attachment depth. Those are detailing changes that consume design hours and can affect schedule.

The heat pump dryer change is a swap on the appliance schedule. The unit floor plan does not change. The plumbing does not change. The architect does not have to rework jamb conditions. The mechanical contractor does not have to redo riser calcs.

Single-line appliance changes are cheap to specify, cheap to procure, and cheap to install. Wall assembly upgrades are not.

When the Wall Upgrade Still Wins

The pattern does not say walls do not matter. It says appliance choice is often the cheaper place to start. There are project conditions where the wall upgrade is the right move.

Buildings well below the dryer efficiency baseline already. If the project is already specified with heat pump dryers, the next HERS lever lives elsewhere, and envelope is back in play.

Code paths that weight envelope harder. Some prescriptive paths and Passive House targets weight envelope performance heavily and care less about appliance specifications. On those paths the math runs differently.

Cold climate projects with high heating loads. When heating energy dominates the building's annual use, every R-value increment carries more weight in the index than it does on a project where end-use loads are spread more evenly.

Buildings where the envelope is already locked. Adaptive reuse, historic shells, or budget-constrained envelopes leave appliances and DHW as the only available levers, regardless of which would have won in a clean-sheet comparison.

The Decision Framework

Most teams chasing a tight HERS target reach for walls, windows, and insulation details first. Those changes are expensive. They consume design time and ripple through structural, architectural, and scheduling decisions. The cheaper points are sometimes sitting on the appliance schedule.

The right HERS strategy on any given project depends on which loads dominate, where the envelope already sits, and which line items can move without forcing redesign. There is no single best path. The only way to know which lever delivers the cheapest HERS points on your project is to model the alternatives before the design is locked in.

If the energy consultant on your project is not modeling appliance type as a variable, the design is probably leaving easy points on the schedule and spending real money to recover them somewhere else.