Why your electric bill spikes in summer (and how much of that is your windows)

August comes around, you open the bill, and the number looks nothing like March. It isn't a utility error and your meter isn't broken: it's climate arithmetic. It's worth understanding where that increase comes from so you know where it can actually be attacked.

The Texas numbers

A Texas household pays an average of $252 a month for electricity in summer, roughly 26% more than the national average. Put another way: the average Texas family spends 3.8% of its income cooling the house, versus 2.9% in the rest of the country.

In the Dallas–Fort Worth area the average bill runs about $170 a month over the year, but from June through September it climbs to a range of $220 to $280. That hundred-dollar jump is almost entirely one thing.

Air conditioning is 50–70% of the summer bill

Everything else — refrigerator, lights, laundry, television — adds up to less than the air conditioner during the hot months. That's why the savings measures that work in summer are the ones that reduce how hard the AC has to work, not the ones that switch appliances off.

And the AC works in direct proportion to how much heat gets into the house. Less heat in, fewer and shorter cycles.

Where the heat gets in

In a typical DFW home, heat comes in through the roof, through the walls, through gaps around doors and windows, and through the window glass itself. The first three are handled with attic insulation and sealing. The fourth is different: glass lets solar radiation straight through.

A single-pane window — the aluminum-and-one-piece-of-glass setup that came with most 1970s and '80s homes in Arlington, Garland or Irving — has nothing to stop that radiation. The sun hits the glass, the glass heats up, and that heat moves into the room. That's why some west-facing bedrooms never cool down no matter how low you set the thermostat: the thermostat is in the hallway and never finds out what's happening in there.

What changes with a double-pane low-E

Two things, and it's worth telling them apart because they aren't the same:

The double pane is two pieces of glass with a sealed space between them. That space — filled with air or argon gas — is a poor conductor of heat, so it slows the transfer. It's what keeps heat from "crossing" the glass.

The low-E coating is a microscopic film of metallic oxide deposited on the glass. It reflects infrared radiation — the sun's heat — back outside, while letting visible light through. That's why the house stays cooler without you having to live in the dark. In a climate like Texas, where the problem is direct sun and not cold, the low-E coating is the part you feel most.

A double pane without low-E helps, but it performs considerably worse here. If you're comparing quotes, ask specifically whether the glass has low-E — some leave it out to lower the price and don't mention it.

The frame counts too

It's the detail almost nobody considers: aluminum conducts heat. You can install the best glass on the market, but if it's mounted in an old aluminum frame, that frame keeps transmitting heat inside all day. That's why replacing only the glass and keeping the original frame only half works.

Vinyl conducts almost nothing, which is why it's the standard for residential replacement in Texas.

What we can't promise you

You'll see ads claiming "up to 50% savings on your bill." We're not going to say that, because there's no way to know it without seeing your home. It depends on:

• how many windows you replace and how big they are
• which way they face (west and south matter far more than north)
• how the attic insulation is holding up
• how efficient and how old your AC equipment is
• what temperature you keep the thermostat at

What can be stated with data is everything above: AC is the majority of your summer bill, and old glass is one of the main routes for the heat that AC has to fight.

Before you spend on windows, check this

We install windows and we'll still say it: if your attic doesn't have enough insulation, that's usually the cheapest investment per dollar saved. If it already does and the bill is still high, then windows are the next place to look.

A good installer will tell you that during the visit instead of selling you everything.