How can you tell whether a new house will actually be energy efficient?

Published September 28, 2026

Summary

Look for things someone outside the builder's office has measured or checked. Window labels show a U-factor and SHGC you can compare with ENERGY STAR's limits for your region, the HVAC contractor should be able to show the load calculation behind the equipment size, and a DOE Efficient New Homes certification means a third-party rater inspected the house before drywall and again at the end. The state energy code only sets the minimum.

Start with the window label

Window performance is rated with two numbers measured under National Fenestration Rating Council methods. U-factor is the rate of heat transfer through the product, so lower means less heat lost. SHGC, the solar heat gain coefficient, is the share of the sun's heat striking the window that makes it inside.

ENERGY STAR's current window criteria, Version 7, took effect October 23, 2023:

Climate region	U-factor	SHGC
Northern	0.22 or lower	0.17 or higher
North-Central	0.25 or lower	0.40 or lower
South-Central	0.28 or lower	0.23 or lower
Southern	0.32 or lower	0.23 or lower

The Northern zone is the only one with a minimum SHGC instead of a maximum. The spec also lets Northern windows qualify with a slightly higher U-factor if the SHGC is higher, for example U-0.25 or U-0.26 paired with an SHGC of at least 0.40.

Ask how the HVAC was sized

The Department of Energy's Building America Solution Center says the HVAC contractor should calculate the home's cooling load with ACCA's Manual J and size the central air conditioner with ACCA's Manual S. If a quote names a tonnage, the contractor should be able to tell you which calculation produced it.

What a third-party certification adds

DOE Efficient New Homes, the program formerly called Zero Energy Ready Home, is voluntary and isn't meant to be adopted as a minimum code. A certified home is verified and field-tested by a rater, a third-party inspector certified under the RESNET/ICC 301 standard, with at least two inspections: one before drywall and one at final.

The current single-family version (Version 2, Rev. 3, released September 2025) also requires ENERGY STAR Single Family New Homes certification (Version 3.2 or 3.3), EPA Indoor airPLUS certification, heating and cooling ducts and air handlers inside the thermal and air barrier, and an HRV or ERV for whole-house ventilation in Climate Zones 6 through 8.

For its energy calculations, the program models a Target Home with infiltration of 2.75 ACH50 in climate zones 1 and 2, 2.25 in zones 3, 4A and 4B, 2.0 in zones 4C through 7, and 1.5 in zone 8. ACH50 means air changes per hour at 50 pascals, a blower-door measurement taken under ANSI/RESNET/ICC Standard 380; lower is tighter. These are reference values for the model, not caps. ENERGY STAR notes that all the hidden air leaks in a house can equal a hole the size of an open window.

The code is the floor

DOE's Building Energy Codes Program tracks which energy code each state has adopted and rates each state code against the national model codes by analyzing the energy use it allows. The article on state cost per square foot lists which code Texas, Florida and California use for homes.