THERE ARE approximately 115,264 facts which the homeowner ideally should know about thermal insulation before, during and after its intallation in the home. And that doesn't include the theories.

By 1980, however, President Carter and the Department of Energy (DOE) would like to see 90 percent of the nation's homes efficiently immune to the weather - in both summer and winter - and Carter has also proposed a tax credit for those who so insulate themselves from any energy crises.

Consequently - for the benefit of those owners of still drafty, poorly insulated, aged or loose jointed homes who were not among the estimated eight-million homeowners who added insulation in the last 2 1/2 years - the government has embarked upon a full scale fact-finding overseeing and quality-controlling mission.

No fewer than eight federal agencies and Congress are concerned with insulation, and representatives of the eight agencies gathered the other day in Washington to talk about their findings, actions, pending regulations and predictions.

All 115,264 facts, unfortunately, were not discussed. But knowing the government's principal concerns about home insulation can be well worth the bureaucratic translation: The government, as it is wont to do, has amassed quite a bit of information about insulation - with more to come. Much of it is available in printed book let form.

And before you understand specifics (the aforementioned 115,264), you should know basics.

1. What is thermal insulation?

Thermal insulation for your home is actually anything that resists heat - it could be a foot-thick concrete shell, but more likely it is obe of the three following types of material used in ceilings, floors and walls to reduce heat loss (or heat gain, in the summer).

The most common type, present in an estimated 70 percent of the nation's 40 million owner-occupied homes, is mineral wool. It can be rock wool, which is made from slag, or fibrous glass, which is spun like cotton candy. Each comes in two forms: loose, in which case it is must be blown into spaces with a hose; or in blanket form (either pre-cut batts or longer rolls). The batts and blankets may have a foil or kraft-paper sheeting on one side called a vapor barrier, which prevents moisture from collecting in insulated walls or ceilings.

Cellulose, which the DOE estimates accounts for 20 percent of current insulation in use, is pulverized or shredded paper or paper fibers, chemically treated to resist fire and vermin. It must be either poured or blown into insulated spaces. It is growing increasingly popular, especially in attics.

Cellular plastics are next most common, and are of three main types. Urea formaldehyde is a foam used most often in walls that are finished inside and out, and therefore difficult to fill with any type of sheet insulation. It must be installed by a contractor. Polysterene and polyurethane are rigid forms of plastic insulation which come in preformed boards or sheets.

The heat-resisting qualities of all types of home insulation are measured - and should be stated on the product - in R values. The higher the R value, the greater the insulation's resistance.

2. Who needs it?

Most homeowners have a choice between doing permanent or temporary battle against the bulge in fuel costs, and against energy waste. Insulation has become so popular no doubt because it is the most permanent weapon in this "moral equivalent of war," and in the long run one of the most cost-effective.

A poorly insulated frame house in Gaithersburg, for example, was fitted with new storm doors and windows and insulated throughout in a recent study done for DOE. The two-year experiment showed energy consumption cut 25.2 percent by the storm windows and 33.3 percent by insulation in the walls, ceiling and floor - total energy consumption dropped 58.5 percent.

The DOE estimates the typical homeowner can cut fuel bills from 10 to 40 percent immediately after improving existing insulation. The installation can pay for itself ine one to seven years, depending on fuel costs, climate, and the previous level of insulation.

The National Bureau of Standards (NBS) puts out a 16-page booklet designed to enable homeowners to calculate how much additional insulation is needed to cope with the country's various "Winter Heating Zones" and "Summer Cooling Zones" based on local fuel and electricity costs. It also allows you to accurately estimate how long the retrofitting job will take to pay for itself, and gives general advice on what types of insulation are best for particular parts of the house. Single copies of the booklet, "Making the Most of Your Energy Dollars in Home Heating & Cooling," are free from the Publications Office, National Bureau of Standards, Washington D.C. 20234.

Weatherization grants, low-interest loan programs and community-development grants are administered by a variety of federal agencies, and are primarily intended to aid the elderly, handicapped or poor who are unable to otherwise insulate. The agencies include the Farmers Home Administration (U.S. Department of Agriculture, Wash. D.C. 20250); the agriculture department's Rural Electrification Administration (Wash. D.C. 20250); the Community Sservices Administration (1200 19th St. NW, Wash D.C. 20506); the DOE's Office of Weatherization Assistance (DOE, Wash. D.C. 20461); HEW's Administration on Aging (Wash. D.C. 20201); and the Department of Housing and Urban Development (Office of Public Affairs, Room 9243, Wash. D.C. 20410).

3. Is Insulation Trouble-Free?

If it were, the federal government would never have gotten involved. Insulation, its manufacturers, suppliers and installers have suddenly found themselves in great demand everywhere, and thus the chances of trouble are multiplied.

Following several formal complaints, the Consumer Product Safety Commission (CPSC) is currently investigating the supposed flammability hazard of cellulose insulation - particularly when improperly treated or installed. Congress is expediting a bill that would expedite the CPSC's investigation and subsequent safety standards report. The General Services Administration and NBS are meanwhile revising testing procedures for determining flammability of both cellulose and mineral wool products.

The flammability potential of all types of insulation, by most government estimates, are increased most often when they're improperly installed. Any type of attic insulation installed too close to a heat source (such as a recessed lighting fixture) is likely to be trouble, as are Fiberglas batts installed with the vapor barriers facing up exposed to sparks from torches or lighted cigarettes. Untreated cellulose fill, which amounts to nothing more than shredded newspaper, would be permanently outlawed by CPSC standards.

At best, improper installation - by do-it-yourself homeowners as well as contractors - will waste your money by saving you less money for fuel than you thought. Installing Fiberglas batts with the vapor barriers facing up into the attic, for example, may cause moisture to collect in your walls and ceilings, or cause an otherwise avoidable fire. The cellular plastic insulation, both foam and rigid, must be installed with a fireproof (sheetrock for instance) covering, because of the danger from the fumes in case of fire.

Common sense and some technical knowledge can constitute the best prevention, and liberal amounts of both can be found in two publications: "In the Bank . . . Or Up the Chimney?" from HUD ($1.70, Government Printing Office, Washington D.C. 20402, document number 023-000-00297-3), and "Insulation Manual, Homes/Apartments" ($4 from the National Association of Home Builders Research Foundation Inc., P.O. Box 1627, Rockville, Md. 20850).

There are also several labeling and advertising problems currently keepingthe CPSC, HUD and the Federal Trade Commission's Bureau or Consumer Protection busy. Although most insulation products are labeled with their respective R value, and most make reasonable energy-saving and thermal-performance claims, a few manufacturers, according to the FTC, have managed to sell loose-fill insulation packaged in unmarked plastic garbage bags. A few others have made some misleading or downright false advertising claims.

If the buyer did indeed beware, it's likely neither the FTC nor the Consumer Product Safety Commission would find much to do.

The FTC is also conducting a "non-public" investigation of trade practices within the Fiberglas insulation industry itself, which is dominated by two or three large manufacturers. Fiberglas shortages last year, says the DOE, resulted when an increase in new housing starts and a new homeowner awareness (caused primarily by last winter's severity) combined to create a huge demand for what previously was a slow-selling product.

To futher complicate things, the Fiberglas shortage has in turn contributed to the still-growing cellulose boom - and to the rise of an estimated 750 cellulose insulation manufacturers most of them small and therefore difficult to keep tabs on.

The insulation business is a lot different today than it was a decade ago. The salesmen, contractors and even the lobbyists talk more rapidly these days. They may skim through discussions of cost per R value, flame spread and foil scrims a little faster than you expected, because they know there's someone waiting for help behind you.

The thing to ask of your government at the moment is information, with which to arm oneself in such fast-moving discussions. It beats the heck out of having to ask your government later for retribution.