FAQs

Below you will find answers to some commonly asked questions about greenhouse heaters. If you have additional questions and would like to talk to a local distributor in your area, click here

General Greenhouse Frequently Asked Questions

Q: What size heater do I need?
A: This depends on the application. To contact your local Modine wholesaler for assistance with sizing and selection, please click here.

Q: Can infrared be used in a greenhouse?
A: Some manufacturers advertise the use of infrared product within a greenhouse but these suppliers typically do not offer other, more suitable equipment. Please refer to "Heating Methods" for more information.

Q: Are products of combustion good for growing plants?
A: Some of the products of combustion are good for growing plants such as CO but they come along with chemicals that may be toxic to your plants. Refer to "Heating Methods" and Unit Heater Efficiency for more information.

Q: Can a gas-fired unit heater be used for under the bench heating?
A: Yes, by running a tube under the bench and supplying air with a blower unit heater. This has the added benefit of moving air which will help with the overall wellness of the greenhouse. Refer to Application Data For Blower Unit Heaters for equipment selection.

Q: Can a unit heater's fan be used even if the thermostat doesn't call for heat?
A: Yes, a summer/winter switch or subase switching may be used to turn the fan on without a call for heat. Refer to Wiring Diagrams, Summer/Winter Switch and Subbase for instructions.

Q: Are there any gas-fired unit heater accessories that can help lower my heating costs?
A: Yes, an energy saver controller may be installed near the ceiling peak to turn on the fan without the burner as heated air becomes stratified. This lowers heating bills three ways: 1) Warm air already created by unit heaters is recycled & redistributed to the plant/occupant level without burning more gas. 2) Interior heat gains from the sun, lighting, occupants, motors, etc. is redistributed and put to beneficial use. 3) By lowering the temperature at the ceiling, the rate of heat loss in the greenhouse is reduced. Click here for instructions.

Q: Does Modine make heaters for use with hot water heating systems?
A: Modine manufactures a variety of horizontal and vertical steam/hot water unit heaters. Click here for product literature.

Q: Are direct-fired heaters really 100% efficient?
A: No. Direct-fired heating equipment requires air changes by code to prevent buildup of harmful products of combustion. Air changes remove warm inside air, and is replaced by cold outside air which needs to be heated to room temperature. Also, the latent heat of vaporization consumes Btu's to maintain water vapor in its gaseous state. Refer to the "Heating Methods" section for further details.

Q: Who do I contact for price and availability?
A: The local Modine wholesaler can assist you with your pricing questions. For assistance please click here.

Q: Who do I contact for installation and service?
A: A qualified installation and service agency must perform all installation and service of these appliances. Your local Modine wholesaler can assist you in finding a qualified service agency.

Q: Are there any side-benefits to using gas-fired unit heaters?
A: Growers can not afford to put their crops in a no-heat situation. A side benefit of using multiple gas-fired unit heaters is redundancy. If one unit fails to operate properly, the remaining units will compensate to keep the greenhouse warm.

Installation & Maintenance Frequently Asked Questions

All installation and service of these units must be performed by a qualified installation and service agency.

Q: How far away must the heater be placed from the greenhouse ceiling and walls?
A: The clearance to combustibles is based on the surface temperature not exceeding 160°F at the specified distance in the unit manual. Check with the greenhouse supplier as to the effects of this temperature on the material.

Q: Does a gas-fired unit heater need to be vented?
A: Yes, while the products of combustion do contain CO2 they also include toxins which may damage the plants or risk the health of occupants.

Q: Can a gas-fired unit heater be mounted below 7 feet?
A: Yes, but it must be properly guarded to prevent injury to occupants of the space.

Q: Can a gas-fired unit heater be mounted outdoors?
A: No, the unit is not weatherproof.

Q: Can a gas-fired unit heater warm air brought in from the outdoors?
A: A blower unit heater may have duct work attached to it to draw in fresh air. Be sure that the static pressure is taken into account during unit selection and setup.

Q: How do I know if there is negative pressure in the greenhouse?
A: One simple method is to see if there is resistance due to airflow when opening or closing a door. Also, if a gravity vented unit is located in the space you may refer to the unit installation instructions on how to check for a good draft.

Q: Why should a stainless steel heat exchanger and burner be used in a greenhouse?
A: Due to the high moisture content of greenhouses, a stainless steel heat exchanger will extend the life of the unit.

Q: Can gas-fired unit heaters be used on natural and propane gas?
A: Yes, it may be set up at the factory for either natural or propane gas or it may be field converted.

Q: May I convert my unit from standing pilot to spark ignition.
A: Yes, but parts for conversion can not be supplied by Modine. Field conversion kits are available from Honeywell, Robertshaw, White-Rogers, and Johnson Controls.

Q: I just converted my gas-fired unit heater from Natural gas to LP. The unit comes on with a high pitch sound and short all blue flames.
A: First check the outlet gas pressure with a manometer to assure unit is firing at a 10" WC. Then adjust the primary air shutters that are on each orifice per installation instructions. Incorrect gas pressure and excessive primary air may cause this problem.

Q: Can I use a temporary LP gas grill tank to run my HD unit until I get my main tank in?
A: No, the demand will cause the small LP tank to freeze up.

Q: During the summer months I need to run the fan only on my unit heater. How can this be done?
A: Modine can supply you with a Summer/Winter switch kit which comes with complete instruction on how to install and operate. See Modine Summer/winter Switch And Subbase Wiring Instructions for information.

Q: What are the inlet and outlet gas pressures?
A: Gas pressures readings are taken using a Manometer, and measured in inches of water column (“ WC). For inlet, this is the gas pressure to inlet side of gas valve. See the installation instructions for maximum and minimum pressures. For outlet, this is the gas pressure that is going through the valve to burner (also called manifold pressure). See the unit installation instructions for pressures.

Q: I cannot get 3.5" WC on the outlet side of the gas valve. The small weak pilot flame will not carry over to the flame rod.
A: Check the inlet gas pressure as it may be too low. This could be caused from improper gas line sizing. See the unit installation instructions for pressures.

Q: I have wired up two unit heaters using one thermostat and it keeps burning out my transformer.
A: You must wire the units using a relay to prevent feed-back to transformer. See Multiple Unit Wiring Instructions.

Q: I just installed a Modine unit that has a propeller fan on it and have determined a blower unit is needed. May I convert this unit to a blower?
A: NO, do not attempt to do this. Replace unit with the correct Model.

Q: I just started up my unit heater for the heating season and the unit will run one minute and flash back and burn at the orifices. In addition, the flame is burning very yellow.
A: Check for dirt or any blockages in: all orifices, burner assembly, exchanger tubes and venting. Also check for incorrect outlet gas pressure, cracks and opened spot welds in the heat exchanger.

Q: In order to save gas, may I block of one of the orifices?
A: NO, it will cause a flash back. Never block any of the orifices.

Q: Is it ok to jumper out the block vent switch?
A: No, this is a safety switch and is reacting to a condition that is causing it to go into the safety mode. Follow the corrective actions listed in the unit installation instructions.

Q: My power exhausted unit runs approximately 10 minutes then cycles off.
A: Check the venting for obstructions and make sure there is a minimum of 1 foot horizontal run off the back of the unit before the vent stack goes vertical.

Q: On a gas-fired unit heater how can the incoming voltage be checked without getting inside the junction box?
A: With a voltage meter check on the terminal between terminal T1 & G. If 24 volts is present you must have supply voltage.

Q: On a Hot Dawg, the hot surface ignition glow bar lights up and the flame comes on for a few seconds then the unit cycles. What could cause this?
A: The power supply polarity is reversed.

Q: The lay out of my building prevents me from venting my gravity vented unit per the installation manual. I can only vent in the horizontal plane.
A: You can vent a gravity vented unit horizontally with the use of an add on power exhauster assembly. Click here for instructions

Q: The Modine manual does not contain instructions on how to set the heat anticipator on the thermostat.
A: The instructions come with the thermostat. If set too low, it may cause unit to short cycle, and cause damage to the thermostat.

Q: The unit transformer keeps blowing. What could cause this?
A: The wire from the thermostat to the transformer on the unit may not be properly sized for the length of run.

Q: To lower the BTU out put, may I go to a smaller orifice size?
A: No, this may cause improper operation of the unit.

Q: To save money, may I install my own unit heater? I know a little about gas and electrical operations.
A: No. A qualified installation and service agency must perform all installation and service on the heater.

Q: What are combustion air requirements?
A: Combustion air is what is used during the burner on cycle and must be replaced. As a rule of thumb, for each cubic foot of gas that is burned, 10 cubic feet of air for combustion is required. See full details in the unit installation instructions.

Q: What happens to the unit if the fan motor does not cycle on while burner is on?
A: The high limit safety switch will trip as it is heat activated, contacts on that switch will open breaking electrical power to the gas valve, resulting in its closing. A possible cause of this problem may be a defective fan timer delay switch that is located inside the electrical junction box on unit.

Q: What is a high altitude kit?
A: This is a kit that Modine can supply for any unit that is installed above 2000' elevation. Click here for instructions

Q: What is a sequence of operation on a Modine gravity vented gas-fired unit heater.
A: The thermostat calls for heat and the burner flame is lit. After approx. 35 second delay, fan motor cycles on. Thermostat is satisfied, burner goes off, and approx 35 second delay, fan motor will cycle off.

Q: What safety devices are on my gravity vented unit?
A: Thermocouple: If a pilot flame is not present, it will prevent gas flow through valve. Limit Control: In safety mode it breaks electrical power to control system. It is activated by an over heating condition. Block Vent Switch: In safety mode it breaks the electrical power to the control system. It is heat activated due to improper venting.

Q: What type of heat exchanger should be used in a chlorinated atmosphere? Should it be a stainless steel exchanger?
A: Never install a unit heater, be it Alum. or Stainless Steel, in a chlorinated atmosphere. It will cause premature heat exchanger failure and not covered under warranty.

Q: When I try to light the pilot, I get a good pilot flame, but when I let up on the gas valve knob to turn it to the on position, pilot flame goes out.
A: 95% of the time it is the thermocouple not putting out enough millivolts to keep electro magnet open in gas valve. Replace thermocouple.

Q: Where can I get replacement parts for my unit heater?
A: You may call your local Modine wholesaler or Representative. Be sure to collect the required Information (complete model number and serial number) prior to calling. Note there is a replacement parts list on the serial plate of the unit. If you are ordering a valve make note if you have converted the unit from one gas to another.

Q: Flames lift off the burner when the unit is started in a cold ambient or has been off for an extended time.
A: If burners port spot welds and outlet gas pressure are ok, you may need to add air shutters to the orifices and adjust to reduce the amount of primary air.

Q: Approximately 4 seconds after the burner goes off there is a loud "PUFF" sound, and sometimes this blows out the pilot light.
A: 95% of the time you see this in an older unit and it is caused by the burner ports opening up, Replace burner. Also check for dirt in orifice, blockage in burner, and correct outlet gas pressure.