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Heating System Maintenance

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Keeping the greenhouse heating system in good repair and operating condition can save money in several ways. Fuel consumed may be reduced as much as 20 percent.  Heat distribution may be more uniform resulting in a lower thermostat setting and better plant growth.  The system is less likely to fail causing crop losses.

A competent service person should clean and adjust all furnaces and boilers at least once a year, preferably in the fall before the winter heating season begins.  The following checklist reviews the most important factors that should be considered.

Use the proper fuel - the use of the wrong grade or type of fuel can result in carbon accumulations decreasing heat transfer.

Protect fuel oil tanks - twenty percent of service calls result from dirty fuel.  Tanks should be away from dusty locations and watertight fittings should be used.  Tanks should also be enclosed or protected to keep fuel from getting too cold.  Parafins in fuel oil may precipitate out clogging the filter.  Propane gas in a partially filled tank may not have adequate pressure.

Remove soot from inside the furnace or boiler - a 1/8" soot deposit can increase fuel consumption as much as ten percent.  Surfaces should be wirebrushed and vacuumed or special cleaning compounds used.

Change fuel filters - uniformly clean fuel delivered to the burner results in more efficient combustion.  Fuel supply line connections should be tight. The oil filter should be replaced each time the furnace is cleaned.

Use correct nozzle size and angle - excessive fuel consumption will result from too large or too small a nozzle.  The spray angle should fit the shape of the fire box.

Clean and adjust controls - check gas valves, thermostats and ignition mechanisms for clean smooth operation.  Inspect safety valves, low-water regulators, limit switches and stack controls frequently.

Oil bearings on motors and pumps - periodic lubrication of bearings increases their life.

Belts - Check fan and blower belts for correct tension and wear.  Replace as necessary. Clean fans and blowers.

Air filters - clean or replace air filters to achieve maximum air flow.

Water must be clean - drain off dirty water through drain cocks in steam and hot water systems.  Flush steam boilers to remove scale and lime deposits. Analyze boiler water periodically to determine if treatment is needed.

Check combustion efficiency - the lower the stack temperature, the lower the fuel consumption, while the higher the carbon dioxide content of the stack gases, the more completely the oil or gas is being burned.  Smoke and soot content of flue gases should also be monitored.

Replace burned oxygen - in poly houses and tight glass and fiberglass houses, install an air intake from outside to near the heater.  Allow 1 square inch of intake area for each 2000 Btu furnace capacity.  Replace existing heating systems with separated combustion units.

Chimney must be high enough - should extend at least 2 feet above the ridge of the greenhouse.  Top of chimney should be at least 8 to 12 feet above the furnace to develop sufficient draft.  Use cap if necessary to prevent back drafts and possible air pollution injury to plants.

Chimney must be tight - any air leaks will chill the gases and reduce the draft. Leaks can also allow plant injuring flue gases into the greenhouse.

Chimney must be correct size - follow the manufacturer's recommendation.  Too small a cross section or a chimney lined with soot will reduce the draft.  Too large a diameter will cool the gases too quickly.

Draft control is necessary - draft variations due to atmospheric conditions can be stabilized by installation of a draft regulator.

Install baffles - turbulators or baffles installed in boiler tubes slow down and direct the flow of gases so that more heat can be absorbed.  Ten to 15 percent savings in fuel consumption can be realized.

Blower timing - in forced warm air systems, blowers should operate until the furnace is cooled to 100 to 120 degrees F or operated continuously to provide air circulation.

Radiator valves are vital to fuel savings - repack leaky valves and replace defective ones.

Clean radiators and pipes - dust and dirt reduce heat transfer and increase fuel consumption.

Insulate distribution lines - in unheated areas and underground, insulate pipes to reduce heat loss.  Each linear foot of a 2" supply pipe insulated in an unheated area can save up to $4 of heat/year.

Thermostat placement - locate thermostats at plant height away from heat pipes and hot air streams.  Shade and aspirate thermostats for most accurate control of temperature.  Install an electronic thermostat with a =/- 1 deg F differential to control temperature more accurately.

Furnace and fan thermostat differential - set exhaust fan thermostat at least 10 degrees above the heater thermostat to prevent simultaneous operation and possible back draft.

Inspection record - keep a record of furnace maintenance and repairs for future reference.

John W. Bartok, Jr., Extension Professor Emeritus & Agricultural Engineer, Department of Natural Resources and the Environment, University of Connecticut, Storrs CT - 2013

Topics: 
Commercial Horticulture
Commercial Horticulture topics: 
Energy
Greenhouse Engineering