How & Why to Adjust the Heat Anticipator on a Room Thermostat InspectAPedia® -
How & Why to Adjust the Heat Anticipator on a Room Thermostat
How to Use a Mini Ammeter to Check Heat Anticipators and Thermostats for Proper Adjustment
How Do I Install & Wire Up a Room Thermostat like the Honeywell Round Wall Thermostat?
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This article explains what a heat anticipator is on a wall thermostat, where to find it, what it looks like, why we adjust the heat anticipator, how we do so. This article continues discussion of the basics of heating or cooling system thermostats, their use, setting, and adjustment. Here we provide A Guide to Finding, Using, and Adjusting Thermostats for Heating & Air Conditioning Furnaces & Boilers, Heat Pumps or Electric Furnaces or Boilers.
This website answers most questions about central heating system troubleshooting, inspection, diagnosis, and repairs. We describe how to inspect
residential heating systems to inform home owners, buyers, and home inspectors of common heating system defects.
The articles at this website describe the basic components of a home heating system,
how to find the rated heating capacity of an heating system by examining various data tags and components, how to recognize common heating system operating or safety defects, and how to save money on home heating costs.
We include product safety recall and other heating system hazards.
Also see GAS PIPING, VALVES, CONTROLS for more details on how to inspect and test LP and natural gas piping, controls, valves, and tanks.
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How & Why to Adjust the Heat Anticipator on a Room Thermostat
Thermostats may also have a "heat anticipator" adjustment which is tuned to the particular heating system to avoid heater on-off oscillating too close to the thermostat's set point.
What is a thermostat heat anticipator? The purpose of a thermostat heat anticipator is to "de-sensitize" the thermostat so that when actual room temperature is hovering close to the set temperature on the thermostat, the thermostat switch won't keep switching the air conditioner or heating system on and off too often - which can damage the equipment.
In our photo you can see our pointer hovering over fine wires wound around a triangular piece of plastic (forming a variable resistor) and you can see at center of the photo a flat copper arm which can be moved to slide a contact to different positions along the wound variable resistor.
The triangular pointer at the top of the copper arm has an opening which helps read the exact position to which the heat anticipator has been set. Behind the pointer you can see a silver scale with different amp readings which are detailed in the table below.
The heat anticipator scale: If you click to enlarge this photo you can see the amperage level to which this heat anticipator had been set when we took this picture. It is below the lowest setting recommended by Honeywell.
How Does the Thermostat Heat Anticipator Actually Work?
The heat anticipator in an electromechanical thermostat includes a tiny heating coil which warms the thermostat's room temperature sensing bimetallic spring. Warming up the thermostat's sensor causes it to "open" its contacts (stop calling for heat) a little before the room temperature actually reaches the thermostat's "set" temperature.
Stopping the call for heat a little early allows for the delivery of residual heat that is already in the boiler or furnace but that has not yet reached the living space. By turning off the call for heat a little early we avoid "overshooting" or making the room warmer than the thermostat's set temperature. The heat anticipator is anticipating the additional heat that is going to arrive and regulating the thermostat accordingly.
When we adjust the heat anticipator on a thermostat that has one, we are fine-tuning the amount of heat anticipation that the device is allowing.
What is the Difference Between the Heat Anticipator and a Heating Control Device Differential?
The differential is the temperature (or pressure) change or "differential" between the LOW and HIGH settings of a heating system control. See Aquastat Functions for an example of control differential settings on heating equipment.
A heat anticipator will not work accurately unless the following conditions are met:
The heating or air conditioning system itself has been adjusted to match the electrical current of the valve or relay which the thermostat is controlling. This is a technical problem for your heating or air conditioning service technician, not something a homeowner can address.
The thermostat is installed at a location where voltage and current (amps) fall on or within the limits of the adjustable heat anticipator
The thermostat is not installed on a power pile system (don't ask).
The heat anticipator on the thermostat should be set to match the requirement & electrical characteristics of the particular heating or air conditioning control circuit that it is switching on and off.
Just below we give a table of heat anticipator settings recommended by Honeywell.
Additional heat anticipator settings and details are usually provided on the thermostat installation pamphlet provided by the manufacturer.
The settings shown here are not likely to be correct for other brands or models of thermostats.
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Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
"Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
Installation Guide for Residential Hydronic Heating Systems
Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)
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