Air conditioning used to be optional in American homes, but now it's nearly universal. The U.S. Department of Energy reports that 87 percent of U.S. households had air conditioning in 2009, up from 68 percent in 1993. With proper maintenance, the typical central air conditioning unit will last anywhere from 15-20 years. Those living in desert climates with scorching summers are looking at the lower end, while residents of northern Minnesota could potentially reach that two-decade mark.

Water heaters, furnaces, heat pumps and other major household components have similar life spans—but if you live in the same house long enough, all of these items will eventually need to be replaced. According to Red Beacon, an online service that connects homeowners with local contractors, the national average for a new heating and cooling system installation is $1,145. That number can reach as high as $4,500 in some regions, depending on the equipment and the contractor.

 

Homeowners who exercise due diligence can save several hundred dollars when major installations are required. These three tips can help you cut costs when the time comes.

Get Multiple Bids

More than 50 percent of new heating and cooling systems in U.S. homes do not perform to their rated efficiency due to faulty installation, Energy Star reports. According to the home improvement consulting firm Energy Vanguard, one of the biggest mistakes contractors make is improper ventilation of HVAC systems. Humidity, dust and higher utility bills are just a few of the problems that can result from improper installation.

Get bids from at least three contractors before making a decision. The Energy Department has a handy checklist of questions to ask each contractor. It's preferable they answer yes to all of them, but the final selection will come down to a combination of price and service level.

Most contractors will ask you about other bids you have received and then lower their prices so they can win the contract. But that also means they have to cut costs on their end. You'll ultimately get what you pay for. Lower installation costs may mean higher utility bills in the long run. It's better to pay a little extra for a job done right.

Timing Is Everything

New bathtubs, showers, toilets and kitchen appliances increase the value of your home and give it a more modern feel. Buying heating and air conditioning equipment from a third party typically negates any warranties the contractor offers on their products—but, that isn't necessarily the case with kitchen and bathroom components.

The best time to buy new appliances is around the holidays. Lowe's has both Black Friday and Cyber Monday deals that can save you upward of 50 percent on select kitchen and bathroom furnishings. You'll have to pay for the items to be delivered (if you don't have a truck), plus the cost of installation. But the money you save buying the items on sale will help lower overall costs. Menard's and Home Depot have similar programs.

Washers and dryers are relatively easy to install yourself. There are numerous Youtube videos on the subject, and Overstock.com provides comprehensive instructions as well. Tubs, showers and toilets are best left to the experts, simply because faulty installation can lead to some nasty issues down the road. But watching a few instructional videos on sink, oven and dishwasher installs is enough for a novice to handle those jobs. Some of the people who produce these videos will even reply relatively quickly to any questions you pose in the comments.

Should You Repair or Replace It?

The decision to repair or replace major households components comes down to age and costs. One rule of thumb: Repair it if the equipment is less than 10 years old and the repair costs are less than one-third of what a new system would cost. Otherwise, replace it.

With this formula in mind, do some research online on the particular appliance that needs repair. Many companies offer guidance in this area. For example, Hot Tub Works offers a repair and replacement guide on spa jets. It's much less expensive to replace the jets on your hot tub than to install a new unit. Likewise, a flickering pilot light or bad heating element on a 7-year-old water heater can easily be repaired for a few hundred dollars.

Finally, never accept a first-and-only offer, and always get everything in writing.