Why is My Electricity Bill So High? Part 2 – Why is My House So Hot in the Summer?

By Vernon Trollinger, June 29, 2016, Energy Efficiency, Save Money

Though we hate to admit it, we’re more frustrated with our monthly electricity bills arrive than we’d like to admit. Besides – it’s easy to forget about your energy usage when you’re busy, and by the time your bill arrives, you’ve either forgotten what you did or you don’t really understand what happened. With our Energy Fails series, we will identify common energy usage concerns to help you prevent them from happening again – saving money on your electricity bills.

Understanding Your Home in Summer

Why is My Electricity Bill So High? Part 2 - Why is My House So Hot in the Summer? | Bounce Energy Blog

You don’t have to suffer through another sweaty summer of high electricity bills.

During the summer cooling season, how does your home lose the heat it absorbs during the day?

Through open spots in the walls, floors, ceiling, and roof. Heat rises and is very slippery, so it will find a way out. Besides, my home is new so it isn’t drafty. **Smug face**

Nope. You’re thinking of the “stack effect”. By the way, heated air rises — not heat. You don’t see hot bricks flying about do you? **Smug face**

Oh… Uh… Well… What about through poorly insulated areas and loose connections in my home’s HVACT system? Doesn’t cool air blowing from the AC vents in my home absorb the heat?

You’re only thinking about the living space. Think more holistically. Think your whole house.

In my whole house? Pfft! The heat doesn’t leave! It bakes the house until it feels like the seven depths of hell.

The Energy Fail: Why IS My House So Hot in the Summer?

In the summer, buildings work like your favorite beverage cooler. Inside, it’s nice and cool as the insulating shell keeps the stifling temperatures out. But buildings absorb LOTS of heat energy during the day. All that heat moves inward through the building’s framing components in the walls, ceiling, joists, and more.

Just how much heat are we talking about? Using my trusty hand-held laster thermometer, I took some surface temperatures of interior walls and an exterior south-facing wall:

Why is My Electricity Bill So High? Part 2 - Why is My House So Hot in the Summer? | Bounce Energy Blog

Just imagine how hot the exterior walls of your home must be!

  • Today’s outside air temperature was 82° F.
  • The inside air temperature was 75° F.
  • Interior walls had surface temperatures between 75° F and 76.6° F.
  • Inside temperature of the exterior south-facing wall was 77.8° F.
  • Outside surface temperature of the exterior south-facing wall was 102.6° F.

Wait — it was only 82° F outside! What’s going on with that wall? And that’s just in Iowa! I can’t even imagine what folks in Texas must experience!

The exterior walls were heating up under the summer sun like a brick — that’s why the exterior wall heated up to 102.6° F — even though the home itself was insulated and air-sealed.  While most people are not surprised that attics can heat up to 150° F, if you ever get the chance to stick your hand inside a wall space on a warm summer day, you’ll find it also gets pretty dang hot in there, too. In fact, your home absorbs radiant and infrared heat all day long just like a big brick in the sun.

This means that, while your home’s AC system is designed to cool air primarily for the living space, it does NOT do a very good job of cooling your home’s structural components. After all, it’s not designed to do that.

How DOES My Home Lose the Heat Absorbed During the Day?

And how does this impact my summer electricity bill?

As soon as the sun’s heat fades and the sun sets, your home radiates its absorbed heat load into the night air — just like a stretch of hot pavement. This is called radiational (or radiative) cooling. Much of the heat is in the infrared spectrum so it’s an even heat that permeates the whole structure.

Two things to try:

  1. If you go outside about an hour after dark, go to the southwest side of your home and touch the outside walls. You should notice that they feel warmer than the surrounding air. If you have aluminum siding, those popping or creaking sounds you hear in the later evening means it’s contracting back to normal after being heated all day.
  2. If your AC has been on all day and if the outside temperature drops to be equal or lower than the inside temperature, turn off the AC and watch your thermostat. Between the hours of 8pm and 11 pm, the inside temperature will rise by as much as 5°F as the whole house radiates its absorbed heat.

How bad can it get? Concentrate a whole bunch of homes or concrete buildings together and you get what are called “urban heat islands” or trapped heat. In some cities, it can be deadly.

How Can I Fix the Energy Fail and Lower My Electricity Bill?

Why is My Electricity Bill So High? Part 2 - Why is My House So Hot in the Summer? | Bounce Energy Blog

Those trees and bushes are more than mere decoration in your landscaping.

Unfortunately, all this heating up during the day and radiating at night adds to your home’s heat load, requiring you to run your AC longer and costing you more money. But we have some suggestions:

  • Block out the sun’s heat by planting trees and shrubs that shade your home.
  • Planting a pair of 25-foot trees on the south eastern and south western corners of your home can reduce your cooling bill.
  • Landscaping your yard can create a microclimate that changes air flow around your house and helps cool those intense temperatures.

Other improvements include using lighter, reflective roofing material, and installing high efficiency low-E windows to help shield your home from the sun’s heat.

Stay tune for next month’s installment of the Energy Fails series, as we’ll discuss why you really need to change your HVAC filter every month.

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About 

A native of Wyomissing Hills, PA, Vernon Trollinger studied writing and film at the University of Iowa, later earning his MA in writing there as well. Following a decade of digging in CRM archaeology, he now writes about green energy technology, home energy efficiency, DIY projects, the natural gas industry, and the electrical grid.

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