Exhibit A that Americans own way too much stuff: The U.S. self-storage industry rakes in more than $44 billion per year.

While some people rent storage units because they are moving to new homes that aren't ready, need to move belongings out of the way during remodels or must park their stuff while temporarily relocating, most pay for the extra space because they've accumulated more property than they can fit into their abodes. That's despite America's average home size ballooning from 983 square feet in 1950 to more than 2,000 today.

Because storage-unit costs are so expensive, the math becomes irrational for many who rent them: After a short time, most will have paid more in rent and fees than their belongings are worth.

If you decide to rent a storage unit, shop around to save. Nonprofit Twin Cities Consumers' Checkbook's undercover shoppers collected prices from a sampling of self-storage companies throughout the area. Here's what they found, plus some shopping and storage tips. You can view Checkbook's full self-storage report and all of Checkbook's ratings and advice until Aug. 5 at Checkbook.org/StarTribune/self-storage.

Shop around

Shoppers found big facility-to-facility cost differences for similarly sized spaces. For example, to rent a 10- by 20-foot unit for a year, prices ranged from $973 to $5,989.

Ask for a discount, then ask again

Without asking, storage companies sometimes offered Checkbook's shoppers half off the first month's rent or the first month for $1. Ask about similar introductory deals. We found some facilities readily offered discounts when our shoppers said they would call other facilities for price quotes.

Competition among storage facilities is fierce, and they highly value new customers. Because it's a pain to shuttle stuff from place to place, storage companies know once someone has rented a unit, they're likely to keep it for months or years.

Check different locations

You might find lower prices (even within the same chain) as you stretch farther into the suburbs. If you don't need to visit your storage unit often, consider grabbing those savings.

Availability drives pricing

Check whether renting two or more separate units is less expensive than one large space. Most facilities use dynamic pricing availability dictates: If a certain type or size of unit is in short supply, it will cost more. Checkbook sometimes found it was cost-effective to lease two smaller units instead of one large one.

Don't assume chains are cheapest

Checkbook found no consistent price winners among the various self-storage chains.

Consider moving up

Ground-floor storage might be more convenient, but storage on higher floors sometimes costs less. So long as units on higher floors are elevator-accessible (and almost all are), the savings might justify the minor inconvenience.

Climate-control costs

Many facilities offer climate-controlled units. That makes them more comfortable to be in when you're moving goods, and it also reduces the risk of damage to your goods from mildew, freezing (for liquids) or heat damage (like for glues on antique furniture). But climate-controlled units typically cost 20% to 40% more.

Indoor vs. outdoor

At some facilities you have a choice between outdoor access (drive up and unload directly) or inside access (located along a hallway). Outdoor access is often more expensive.

Long-term commitment

Some storage spots offer lower rates if you commit to six months or a year or prepay several months' rent.

Beware extra fees

Many facilities charge one-time "administration," "set up" or "processing" fees. These junk fees were, for the most part, modest, but check anyway.

Check insurance coverage

If you have a homeowners or renters insurance policy that covers your personal property away from your house, you probably don't need to buy extra coverage from the storage company. Ask your insurer to make sure. If not, you can buy insurance from the storage company. It's usually an expensive add-on: At several facilities, a modest $15,000 of coverage cost more than $25 per month.

Check access hours

If you'll need odd-hours access, know that some spots aren't open 24/7.

Consider alternatives

Other options exist for parking your odds and ends. If you need to clear space for a remodel, you can rent a mobile storage container for your driveway. They cost about half what you'd pay at a self-storage facility. And if you want to hire someone to do all this schlepping and storing for you, moving companies usually offer that.

Twin Cities Consumers' Checkbook magazine and Checkbook.org is a nonprofit organization with a mission to help consumers get the best service and lowest prices. We are supported by consumers and take no money from the service providers we evaluate. Star Tribune readers can access all of Checkbook's ratings and advice free until Aug. 5 at Checkbook.org/StarTribune/self-storage.