January 2001

Volume 10, Number 1

Thermostatic By-Pass Valve for Hydronic Baseboard Heat

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Thermostatic By-Pass Valve for Hydronic Baseboard Heat


The EnerJee 3-Way Thermostatic By-Pass Valve allows more precise control of space heating temperatures within a particular hydronic heating zone. This mock-up installation (with and without cover) shows how a section of fin-tube radiator is by-passed. Hot water flow in this configuration would be from right to left.

Source: EnerJee

Separately regulating temperatures in different rooms within a single heating zone has long been difficult. Louvers on the radiators generally prove ineffective. Along with causing overheating, the inability to provide precise zone control can also waste a lot of energy—for example, where there are little-used rooms that can be closed off and don’t need to be kept as warm as occupied spaces. The specialty heating component supplier EnerJee, of Morrisville, Pennsylvania, offers an elegant solution to this problem. Their No. 320 liquid-filled, thermostatically controlled, 3-way by-pass valve allows hot water to be shunted past a section of fin-tube baseboard radiator through a parallel section of pipe when less heat is called for.

The quick-response thermostat is nonelectric and requires no wiring. It features stepless temperature settings of 1 to 5—representing a range of 43°F (6°C) to 79°F (26°C)—and can be used with most new or existing fin-tube baseboard installations. The thermostatic valve has a list price of $60. Installation also involves plumbing in a section of 34-inch (19 mm) copper piping and various fittings, cutting a hole through the radiator cover for the thermostatic control, plus labor. Anthony Filice of Park Plumbing and Heating in Harrison, New York told EBN that installation is fairly time-consuming because the system has to be drained. The thermostatic valve has compression fittings, but soldering is needed for other piping connections (see photo). Filice estimates that it would take 4 to 5 hours to install several of these by-pass valves in a house. The added by-pass piping is hidden within the standard baseboard radiator cover.

Filice likes the product a lot. In fact, he installed these valves in his own home. With four bedrooms on one zone, he had long dealt with some rooms being too hot and others too cold. Now, all the rooms can easily be kept comfortable. He noted that because the thermostat is at the radiator, settings need to be based on comfort—even though #3 on the dial is supposed to be 68°F (20°C), you might need a higher setting to keep the room at that temperature.

This EnerJee thermostatic by-pass valve is sold primarily for residential applications, according to EnerJee president John Engelberger, P.E., but it is also used in some commercial buildings. Though the valve has been on the market for two or three years, Engelberger has been disappointed with sales. (With energy prices back in the news, a product like this may begin attracting more attention now.) The product is sold through distributors; contact the manufacturer to find out about local availability. – AW

For more information:

John Engelberger, President


24 S. Lafayette Avenue

Morrisville, PA 19067

215/295-0557, 215/736-2328 (fax)


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January 1, 2001