The Dead Men chose this system because it combined heating with ventilation, both of which were very important folks who could afford central heating in those days. The name "indirect" comes from these meteorite-sized hunks of iron that hung in the basement and directed warm air upstairs to the first, second, and sometimes even the third floor of a big house. The air moved through tin or sheet-iron ductwork that is a joy to behold. Such workmanship! And more often than not, the Dead Men brought in fresh air from the outside to mingle with the basement air and provide ventilation to the rich folks upstairs. At the time, this central heating system was the absolute best that money could buy.

Most of the indirect radiators were put together just like small cast-iron sectional boilers. Some, however, were made of rows of steel fin-tube. In every case, though, it's tough to figure out what size they are because you can't see them and very little information from their manufacturers remains. And you're not about to start trashing that wonderful ductwork, are you?

Here are some things I know for sure, though:

If a steam system served the house, the indirect radiators had to be at least 14 inches higher than the boiler water line. That was to allow for the gravity return of condensate back to the boiler. Most of these systems worked on low-pressure steam vapor. Several ounces did the trick. If you're replacing an old boiler you have to be very careful where you position the new boiler's water line because indirect radiators often hang very low. If you set your replacement boiler too high, it may partially fill the indirect radiator with water and that will seriously cut down on the heat.

Within the duct, the indirect radiator has to be a good 10 inches below the top, and eight inches above the bottom. The radiators had to be tight against the sides of the duct. These dimensions are crucial to the proper flow of air across the indirect radiator. Sometimes, a cast-iron unit will fail and you might want to replace it with a homemade nest of fin-tube radiation. Watch what you're doing in a case like this because the flow of air is so subtle here - and so important.