A more efficient heating system

I've heard about an all-new concept in gas hot-water heating in which the gas is burned in a controlled series of explosions. It is so efficient, I understand , that you can even hold your hand on the flue. The cost is approximately $3,000 . Can you tell me anything about the system? Richard H. Schmidt Batavia, Ill.

What you're talking about is referred to as "pulse combustion." So far as I can find out it is not yet available in a water heater, probably because of the cost. However, there is a pulse-combustion boiler which may be likened to an internal-combustion engine in which there is, as you say, a continuing series of explosions.

The system is very efficient in that most of the heat is extracted. What would be called the flue is made of polyvinylchloride (PVC) plastic and, indeed, you can put your hand on it. The temperature may be less than 90 degrees F., I am told.

The pulse-combustion concept provides a better way of transferring more heat to the water in the boiler instead of most of it going up the chimney.

One company, Hydro Therm, Rockland Avenue, Northvale, N.J. 07647, has such a unit on the market. Phone: (20l) 768-5500.

There also are a numher of furnace manufacturers that are working on such a system for hot-air furnaces as well in which the unit would draw more heat out of the flue gases.

As you point out, the system is more costly than a conventional system.

I"ve been told there is talk of applying the technology to a hot-water heater as well but that the reason it is not on the market is probably cost. A new conventional water heater costs $150 or $200. If you add the pulse-combustion technology to it, the cost could make t he unit noncompetitive.