After heating and air conditioning our homes, what do we spend most of our energy money on? For most Americans, it's the hot-water heater. In many cases, we spend more on hot water than we do on gasoline for our cars. Yet the old hot-water tank gets relatively little attention as a potential energy saver. Every time we take a shower, wash the dishes or do the laundry, great gobs of heat quite literally go down the drain.

At first it looked as though solar hot-water heaters were the answer. Once installed, these heaters could save at least 50 percent on hot-water bills. But solar heaters are expensive -- at least $2,000 to install.

Congress came along and gave an energy tax credit for the daring homeowners who installed expensive solar hot-water heaters. The credit ante was raised again this year to 40 percent of the cost.

So if you buy a $2,000 solar hot-water heater, you will get 40 percent off your tax bill for a net cost of $1,200. It's a nice saving but at $1,200 the cheapest solar heater is still three times the cost of a regular electric or gas heater.

It would take you 10 years or more of energy savings to get back your initial investment on a solar hot-water heater (varies depending on where you live and how much water you use).

Maybe sometime in the future when electricity, oil and gas supplies cost a lot more than they do today and the solar-energy business can mass produce water heaters at lower prices, it will pay to install a solar hot-water heater (it already does in parts of the Sunbelt area of the country).

But right now the most promising development in hot-water heaters is the heat pump. The heat pump, which sucks heat from the surrounding air to warm the water, has been around for quite awhile. But it wasn't until recently that it has been priced right and extensively marketed.

The heat pump, which stands about 3 feet high and is about 2 feet across and 1 foot deep, can be attached next to your current electric hot-water heater or oil-fired heater. It can also be attached to a gas-fired heater but, at today's gas prices, you probably won't save money. Manufacturers have even developed installation kits for do-it-yourselfers. One hose goes on the bottom of your water tank and another goes on the top. Cold water is pulled into the machine from the bottom of the tank, is warmed by heat pulled out of the air, and is pumped up into the top of the tank where you draw it off for washing.

In my area, you can buy a hot-water heat pump for around $650 installed. That's just about half of what a solar heater would cost and you get similar savings on energy bills -- 50 percent or so.

In the winter, heat pumps for hot water are less efficient because they return cold air into your home. But if a heat pump is installed in, say, a basement where there is wasted heat in a furnace room, the usefulness is increased.

In summer, a heat pump is most efficient because it not only heats your water, it helps cool your home. It also dehumidifies your basement, utility area or wherever it's put. According to an excellent article in the January 1980 issue of Popular Science magazine, one of the first successful hot-water heat pumps was marketed by E-Tech of Atlanta. Others, such as Fedders, Northrup and Energy Utilization Systems now have competitive units on the market.

Q. I've just got to cut our automobile insurance costs. We have two cars and a couple of kids who drive. We're bound to have a minor accident and our costs will go even higher. What's the best way to reduce our premium cost short of getting rid of the cars?

A. The first thing you have to look at is your deductible. Many policies still carry $100 deductible clauses which means you pay the first $100 and the insurance company pays the rest. These low-deductible policies can be quite expensive. If you can afford to cough up $500 at any given time to cover the costs of an accident, you can cut your insurance costs by raising your deductible to that amount.

In my area, here's an illustration how it would work for a male driver over 30 who uses the car (1979 model) primarily for commuting. The collision coverage with a $100 deductible costs $104 a year. With a $500 deductible, it only costs $57. Quite a saving. Full, comprehensive coverage (fire and theft) costs $50 a year. With a $200 deductible it only costs $18 a year. Installing anti-theft devices, such as an automatic gas-cutoff mechanism, can get you a 15 percent discount with some insurance companies. You also pay higher insurance premiums for some cars compared to others. For example, a Chevrolet Corvette or a sporty Datsun 280-ZX cost 25 percent more to insure than most American-made, four-door sedans. Ask your insurance company for the automobile "risk list." It's an eye-opener.

Q. We are forming a carpool at the place where we work and want to know if there will be any problems with the insurance?

A. There shouldn't be if you have the kind of pool where everybody takes their turn. Passengers are viewed as the driver's guests and are covered by the driver's insurance policy (which should have at least $300,000 coverage for total liability).

If you are planning a "van pool" where one driver does all the work and gets reimbursed by the passengers, you should get more liability coverage. Some states require van pool drivers (with as many as 12 to 14 passengers) to have a commercial license, and pass a more stringent driver's test. Some companies that lease vans to carpools (the best way to go about it) require as much as $2 million liability coverage because of the increased exposure (more passengers, more miles driven). They also require regular maintenance checks.

Q. What's the best type of carpet material to purchase for a heavily used family room?

A. The professional decorators tell me nylon is the toughest and least expensive type of quality carpet for a much-used family room.

They say Antron nylon has the highest wearability rating and currently sells for $14 to $20 a square yard. With proper maintenance, this material should last for 10 years or so. There is one drawback. Nylon can stir up quite a bit of static electricity in the winter when it's so dry inside (unless you have a humidifier). This static electricity tends to pick up dirt and your carpet may need more frequent cleaning than other types. Closely woven, short-pile carpets hide dirt and will wear well in family rooms or children's rooms. Dense, commercial plush carpets wear extremely well and might be worth investigating.