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It’s a double whammy: Home energy costs are rising just when most of us can least afford it.

With budgets tightening, it’s hard to lay out money upfront for energy-saving home improvements, even if we know they’re a wise investment. So we posed this question to Chris Kielich, a spokeswoman for the U.S. Department of Energy:

If a homeowner had only $250 to spend on energy-saving measures, what would produce the biggest bang for the buck?

Here’s what she suggested. (Note: Costs are approximate.)

Programmable thermostat, $35

A programmable thermostat saves not only fuel but also human energy. No more changing the thermostat before you leave for work or go to bed. The device does it for you.

Most thermostats allow you to store multiple settings each day, and they typically have a manual override so you change the temperature without canceling the whole program.

Installing a programmable thermostat requires fairly basic electrical skills — about the same as replacing a light switch or fixture. If you need to hire an electrician to install it, you’ll need to figure that into the cost.

If you set back your thermostat eight hours a day, figure on saving about 1 percent of your heating costs for each degree you lower the temperature, the Energy Department says. You’ll also save on cooling costs by raising the temperature, but the department doesn’t provide a specific figure.

Sealants, $42

Every house has little openings letting air in and out. Closing those gaps keeps more of your air inside, where it belongs.

Choose a cool, very windy day to do a little sleuthing for gaps with the help of an incense stick, the Energy Department suggests.

Turn off your furnace, shut all the windows and doors, and turn on all exhaust fans that vent to the outside. Move the lighted incense stick near common leak sites, including the edges of doors, windows and chimneys, the places where pipes or wires enter the house, and the joint between the foundation and the walls. Wherever smoke is sucked from or blown into the room, there’s a draft.

Caulk is generally adequate for sealing smaller cracks. For larger gaps, use spray insulating foam. The foam comes in a non-expanding type for windows and doors and an expandable type for other gaps.

Weatherstripping seals the gaps between doors or operable windows and their frames.

Count on your payback coming in comfort as well as in energy savings.

Landscaping, $75-$150

We don’t often think of what’s outside our homes as affecting our energy costs inside, but a well-placed plant can provide cooling shade.

Kielich recommended shading the outdoor unit of a central air conditioning system with a trellis and climbing vine. Shading the unit will increase its efficiency by as much as 10 percent, the Energy Department says.

Make sure to leave enough space around the unit so air flow isn’t impeded.

Plant that vine or a shade tree on the south side of the house to shade windows and, when the tree grows, the roof. In our part of the country, choose a deciduous tree so the sun’s warmth can reach the house in winter when the leaves are off.

A slower-growing tree will probably live longer, tolerate drought better and remain stronger in wind or heavy snow, the Energy Department notes.

We figured on spending $50 on a simple trellis and $25 on a good-size vine, such as clematis or fast-growing wisteria for a sunny spot or climbing hydrangea for shade. A shade tree such as maple or pear could set you back $150 or even more, but you’re likely to find sales at garden centers if you shop in the fall. Besides, the cooler, moist conditions make autumn an ideal time to plant trees and perennial vines.

You can find more ideas at apps1.eere.energy.gov/consumer/your — home.

Compact fluorescent light bulbs, $30

A good compact fluorescent bulb typically uses one-fourth to one-third the electricity of a standard incandescent bulb and lasts six to 10 times as long — about five years with typical use. That means each bulb will save you roughly $6 a year in electricity, or $30 over the bulb’s lifetime.

Kielich recommended replacing the bulbs in the lamps and light fixtures you use most often. “It might cost some money to start with, but you’re going to start saving [on electricity] immediately,” she said.

Some tips: Look for the Energy Star label, which signifies the bulb has met certain standards for quality and light color. If you have an outdoor fixture or a fixture with a dimmer, buy a bulb made for that purpose. And know that because fluorescent bulbs contain mercury, you’ll need to dispose of them as hazardous waste.

We figured investing in five bulbs at $6 apiece was a reasonable start. That investment should pay for itself the first year and cut your electrical usage by $150 over five years, for a net savings of $120.