New Insulation Not Lowering Your Energy Bill? Six Reasons, and What to Check

The Short Answer

When new insulation does not seem to lower the bill, it is usually one of three things: the comparison is misleading (weather and rates changed), the air leaks were never sealed, or the insulation went in with gaps and compression that cut its performance.

It also helps to know what to expect. The EPA’s estimate for air sealing plus insulation together is an average of 15% on heating and cooling costs, or about 11% of total energy costs. Insulation on its own, over unsealed leaks, will do less than that.

Reason 1: You’re Comparing the Wrong Months

A colder winter or a hotter summer can wipe out a real saving on paper. EIA explains that degree days are measures of how cold or warm a location is; a winter with more heating degree days needs more heating no matter how well the house is insulated.

• Compare kWh, therms or gallons, not dollars, so rate increases don’t hide the saving.
• Compare the same months year over year. One utility’s guidance is to make sure you’re comparing similar months, like February to February.
• If your bill shows heating degree days or average temperature, divide usage by degree days for a fairer comparison.

Reason 2: The Air Leaks Weren’t Sealed First

Fluffy insulation slows heat conduction but does not stop air. The Building America Solution Center notes that the porous blown or batt insulation typically used will do little to stop the movement of conditioned air out of the home. Its attic checklist is blunter: fibrous insulation is not an air barrier and must not be used for air sealing.

That is why ENERGY STAR recommends you complete an attic sealing project before adding attic insulation. If your installer blew insulation over open top plates, wiring holes, plumbing chases and an unsealed hatch, warm air is still escaping straight through it.

Reason 3: Gaps, Voids and Compression

Insulation only reaches its rated R-value when it fills the space evenly. The RESNET Grade I standard, as described by the Building America Solution Center, is to install insulation without misalignments, compressions, gaps, or voids. It adds that poorly installed insulation can result in higher heating and cooling costs.

• Batts squashed under stored boxes or plywood decking.
• Bare spots around the hatch, at the edges and behind kneewalls.
• Insulation disturbed by later work, such as an electrician or cable installer.

Reason 4: Wind Washing at the Eaves

In a vented attic, outside air comes in at the soffits. Without baffles, it blows through the insulation at the edge of the ceiling, right above your exterior walls. The Building America guide notes that baffles also help to protect the insulation from wind washing. Check that there are baffles at the eaves and that the insulation runs right to the top of the wall.

Reason 5: The Ducts Are in the Attic

If your furnace or air conditioner pushes air through ducts in the attic, leaky or poorly insulated ducts can lose much of the benefit. Insulating the attic floor does nothing for heat lost from ducts sitting on top of it. See our duct sealing guide.

Reason 6: Heating and Cooling Is Only Half the Bill

According to EIA, more than half—52% in 2020—of a household’s annual energy consumption is for space heating and air conditioning. The rest is water heating, appliances, lighting and electronics, which insulation does not touch. A 15% cut in heating and cooling is closer to 7 or 8% of the whole bill.

If your bill rose for reasons unrelated to heating, look at rates and big loads. Our bill-doubled guide and 2026 rate hike guide cover those.

What to Do Next

1. Redo the comparison in kWh or therms, same months, adjusted for weather.
2. Go into the attic (safely) and look: is the depth even, are the joists buried, are there baffles, is the hatch sealed and insulated? Compare with ENERGY STAR’s recommended R-values.
3. Look for air leaks with incense or a thermal camera on a cold day.
4. If the work was done by a contractor, ask for a blower door test. A good contractor will come back to seal leaks and fix gaps.

Tools That Help

We may earn a commission if you buy through these links, at no extra cost to you. Products are chosen on published specifications; we do not test them in-house (how we choose).

Klein Tools TI250 Thermal Imager

On a cold day, shows thin spots, voids and air leaks in ceilings and walls.

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Frost King V443/4 Vinyl Foam Tape (4-pack)

For the attic hatch, one of the most common leaks left behind after an insulation job.

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Frequently Asked Questions

Why didn't my energy bill go down after adding insulation?

Common reasons: the comparison ignores weather or rate changes, air leaks were not sealed first, the insulation has gaps or is compressed, wind is washing through it at the eaves, or leaky ducts in the attic are losing heat.

Does insulation stop air leaks?

No. Fibrous insulation such as fiberglass or cellulose is not an air barrier. Air leaks must be sealed with caulk, foam or rigid materials before the insulation goes in.

How much should insulation save?

The EPA estimates an average 15% saving on heating and cooling costs from air sealing and insulating together, about 11% of total energy costs. Insulation without air sealing saves less.

How do I compare bills fairly before and after insulation?

Compare energy units (kWh, therms) for the same months year over year, and adjust for weather using heating or cooling degree days.

What is wind washing?

Outdoor air entering through soffit vents and blowing through the insulation at the edge of the attic. Baffles at the eaves prevent it.

Related Guides

• Attic air sealing cost — sealing done properly
• Attic insulation and your utility bill — getting the level right
• How to seal an attic hatch — the most common leftover leak
• How to find thermal leaks — tools and methods

Sources

• ENERGY STAR: Methodology for estimated savings
• ENERGY STAR: Attic insulation project
• ENERGY STAR: Recommended insulation R-values
• Building America Solution Center: Air sealing and insulating ceilings in vented attics
• Building America Solution Center: Attic air sealing and insulation checklist
• Building America Solution Center: RESNET Grade I insulation installation
• EIA: Use of energy in homes
• EIA: Degree days
• North Shore Gas: Degree days