Clow Gasteam Radiator Notes

Long Beach Ed

We've been rebuilding one of these in the shop for use in an old glassed porch in my own home, and want to share notes about these unusual pieces of history. Clow Gasteam Radiators were steam radiators equipped with their own internal iron gas burner; basically a combination boiler/radiator.

For a time in the 1930s and 40s, Clow advertised them as Gasteam Heating Systems. They were sized to generate steam to an additional separate radiator of 50% capacity if desired.

Clow radiators are history. Two types were made, vented and unvented. The unvented ones — by far the most common — as any unvented heater, spill "products of combustion" - carbon monoxide, nitrogen oxides, sulfur oxides, VOCs and moisture into your lungs. This can be unhealthy or deadly under certain conditions. These can be more dangerous than modern unvented gas appliances. They lack most safety features found on modern heaters. Built from 1900 through the 1960's, early ones lacked pilot lights or gas safety valves.

If you choose to use an unvented heater of any kind, you should research the health risks and ways to minimize them. You must also understand that most of these heaters have NONE of the typical safety features required in gas appliances after the 1950s.

I sought out a vented radiator to restore and found a nice 1949 example of the smallest one offered (24 sq ft, 12,000 BTU), equipped with a mechanical thermostat. A Clow Baso pilot safety valve and thermocouple were added, donated by another collector. Original Model 2-ES "Snap Action" mechanical thermostat valves were furnished by Robertshaw; mine had a similar 1950s era Honeywell.

Here are some data about these unusual heaters:

Burner firing is controlled by a diaphragm pressure valve. Steam pressure moves a twin metallic diaphragm that reduces gas flow to the burner by blocking an orifice. Early ones reduced flame at 3 - 5 psi of steam, later ones at 5 - 8 lbs of steam. Pressure never completely closes gas flow, even with the radiator covered; a separate bypass orifice keeps a small amount of gas flowing to maintain a pilot burner.

Some late regulators were equipped with a bi-metallic element limiting gas on excessive temperature, preventing overheating should the water level be neglected. This was an effort to address overheated dry appliances setting window curtains aflame.

The lower nipples of the radiator, and a small internal reservoir above the internal burner would be filled with an inch of water that would boil to produce steam. Casting design prevented cracking if freezing temperatures were encountered. Water content is about a half-pint per section. Radiators were furnished with a conventional steam/air vent. Late models came with vacuum steam vents permitting extended steam production.

Fuel type (natural gas, manufactured gas, LP) and radiator size determines the gas orifice size that was provided by Clow. Several types of pilot burners were used. The later burners had an internal block that split the first row of burners from the remainder; the first row (clocked at 4,000 BTU) served as a pilot, or in some later literature as a "low setting". A 1/4" tube that bypassed the regulator supplied this pilot.

Fuel trains varied over the years. The most recent models were offered with mechanical thermostats or electric solenoid valves and pilot safety valves. The radiators were spray painted silver by Clow after the gas train's installation. Clow's casting year is usually cast onto the left section.

Later units have both the main burner and pilot portion with separate air shutters for combustion air regulation. Burner air should be adjusted as you would any atmospheric burner with combustion instruments to minimize carbon monoxide production. Adjustment of this unit's cast iron burner shutter yields very low CO — about 9ppm into the flue. No adjustment of the air shutter was capable of producing objectionable CO output. Efficiency was calculated as 62%, which roughly matches the manufacturer's catalogue listing data.

Each radiator was equipped with a relief valve. Some had a calibrated stainless spring playing on a machined disk and seat set to open at 20 psi. Others had a simple replaceable threaded solder plug. Needless to say, old safety valves should be tested and/or replaced in any restoration. Modern replacements are available and could be a good idea.

Very early versions were two and three column castings available for hot water (which required an external reservoir) or steam. Four, five and six column castings replaced them, and finally around 1934 six column patterns were used exclusively. These were still being sold into the 1960s.

The manufacturer also advertised them for use in combination with a regular one or two pipe steam system, to be piped along with standard radiators from a boiler. Alternately they could operate alone by gas by closing the steam system's valve.

There is much more that can be said about these unique pieces of heating history. I'll leave the warnings to others. There's at least one fellow who has beautifully restored a band of these and other gas heaters. They're said to follow him home. He's been an infinite help in this project.

Here's an engineering brochure illustrating models and operation from 1934:

https://archive.org/details/ClowGasteamHeatingSystems/mode/2up?view=theater

Playing with antique, obsolete and inherently hazardous gas appliances isn't for someone without a good understanding of the dangers and risks.

.

Long Beach Ed

ChrisJ

What continues to confuse me about these is the reason to use steam is to transport heat from a remote location to another.

What's the reason in a self contained unit? I understand electric radiators use oil to distribute the heat around the unit evenly and cool the heating element, but is that necessary with a huge hunk of cast iron and a small gas burner?

delcrossv

So,that'd take a 90 to a vertical exhaust?

Very spiffy with the chrome piping!

Long Beach Ed

Yes, according to their manuals. You need to create some draft or the exhaust spills inside. The casting has a patented internal draft diverter (sucks half the heat out of the room too) . So you'd vent it similar to a gas water heater. Sometimes into a tee with a condensate drip. I'm using an exterior B vent.

I thought the chrome would be a nice touch. Spiffy is a Clow's middle name.