Applications

• Commercial Space Heating
• Greenhouses and other Agricultural
• Industrial Space Heating

Overview

The good old standard for industrial and commercial shop heating is the unit heater.  The unit heater is available in sizes of about 25,000 BTU increments from about 10,000 BTUs to over 600,000 BTUs in a single unit.

They are quick and easy to install and operate; they can be easily moved and are highly modularized to get any amount of heat needed.   They require no floor space.   However, they are also about the lowest efficiency heating system for large spaces.
Their small fan limits the amount of air Unit Space Heater that can be circulated, so temperature stratification and hot/cold spots are common with unit heaters.   Filters are not typically used, so heat exchangers can become dirty and lower efficiency.   New advances in unit heaters have made them more efficient, such as forced draft burners and double heat exchanges.  Most now also have IID ignitions, which was a code requirement by benefited maintenance/ convenience improvement more than efficiency   (it is difficult to relight pilots on ceiling suspended units).

The unit heaters in the photo to the right have heat exchangers installed on the flue, which preheats incoming combustion air.

Unit heaters are often found in older industrial facilities that also have negative air pressure, which causes unit heaters to back-draft through their flue, and cause premature heat exchanger failure.

Unit heaters are about the lowest first cost heating system available. Sized correctly for the space and maintained, they can be an effective system to operate.

Unit heaters are best suited for smaller industrial and commercial facilities with relatively low ceilings or larger places if even temperature distribution is not critical.

High Efficiency Unit Heaters

A standard unit heater has a combustion efficiency of maybe 80% in lab conditions and due to all the problems mentioned above, the seasonal efficiency could be in the range of 50%. Condensing unit heaters have advanced burner and heat exchangers designed to drop the flue gas temperature below 212F. When flue gasses condense, they also give up the latent heat of vaporization, which is another 970 BTUs per pound of water condensed. The unit heater’s heat exchanger must be able to handle the slightly acidic water and there must be a drain connection.

The Reznor UEAS line of unit heaters claim a combustion efficiency of 93%.

Reznor® V3 Series Model UEAS gas-fired separated combustion unit heaters are available in 4 sizes ranging from 130,000 to 310,000 BTUH gas input. Heaters are designed for up to 93% thermal efficiency and are approved for installation in the United States and Canada by ETL.

Manufacturers

Reznor
Telephone: 800-695-1901

Web site: www.rezspec.com

Modine Unit Heaters

For price and spec information from a Modine distributor with a very nice web site, see:

Aarons Creek Farms, Inc.
380 Greenhouse Drive
Buffalo Junction, VA 24529
Telephone: 888-888-9050

www.littlegreenhouse.com/accessory/heaters.shtml

Source: Bob Fegan 1/2009; photo Bob Fegan; Reznor images from their web site 5/2009;