Browse Categories

Reverse acting vs Direct Pneumatic Thermostats

pneumatic thermostats calibrating pneumatic thermostats how pneumatic thermostats work

What’s the Difference (and Why It Matters)?

If you’ve ever worked with pneumatic controls, you’ve probably come across this question:
What’s the difference between a direct acting and reverse acting thermostat?

It’s one of the most common questions we get at our sales counters and for good reason. Understanding this concept can save you time, prevent misdiagnosis, and help your system operate correctly.

 Direct Acting 

What is a Direct Acting Thermostat?

A direct acting thermostat increases its output as temperature increases.

Simple way to think about it:
Temperature goes up = Output goes up

Where you’ll see it:
Direct acting thermostats are most commonly used in cooling applications.

Example:
Room temperature rises above setpoint
Thermostat increases output
Cooling system turns on

In a BAS system: As temperature increases = signal increases
 Reverse Acting 

What is a Reverse Acting Thermostat?

A reverse acting thermostat does the opposite...it decreases its output as temperature increases.

Simple way to think about it:
 Temperature goes up = Output goes down

Where you’ll see it:
Reverse acting thermostats are typically used in heating applications.

Example:
Room temperature drops below setpoint
Thermostat increases output to call for heat
Heating system turns on

In a BAS system: As temperature decreases = signal increases
Common Mistakes (and how to fix them)

Pro Tip:

If a valve or actuator seems to be working backwards, the issue is often not the hardware—it’s the setup.

 The controller point may be set to the wrong action (direct vs reverse).

Before replacing parts, always check:
  • Control configuration
  • Signal direction
  • Application type (heating vs cooling)
Why This Matters:
  • Proper system operation
  • Faster troubleshooting
  • Fewer unnecessary part replacements
Final Thoughts: Direct vs. reverse acting thermostats is a simple concept—but it plays a big role in how HVAC systems function.

Remember: 

Direct = temperature and output move together

Reverse = temperature and output move opposite

YouTube Video   Pneumatic Thermostats

Tags

bas networking iot distech control valves building automation ot tosi jace hvac systems industrial valves eclypse tosibox jci bas network belimo fuel train control 8000 9000 dwyeromega remote display hvac pumps hydronic systems commercial hvac centrifugal pumps chilled water systems heating water systems boiler safety boiler components industrial heating equipment heating systems chiller Pneumatic Electro-Mechanical and DDC systems maintenance calibration remote bacnet n4 automation honeywell control panels network configuration port security network control smart buildings energy management ethernet based bas network guidelines managed switches optimizer commander johnson controls pressure transmitter transducer link config IAQ Indoor Air Quality IAQ sensors Filtration Ventilation bypass valve hydrolic system mixing valve diverting valve KMC Control lines Conquest Commander KMC software solutions engineer panel Lead/Lag HVAC pumps boilers chillers RTUs hvac controls globe valves hvac valves pneumatic thermostats calibrating pneumatic thermostats how pneumatic thermostats work tosi control sma device count points Gas Meters Diaphragm Rotary meters gas trains gas supply commercial boiler burner ief transmitters Gas Valves for boilers Vent Valves Pilot Gas Valves switches for boilers a temperature sensor honeywell i4006 honeywell l6006c honeywell l91b temperature limit switches gas pressure limit switches pump selection pump sizing hydronic pump design pump fundamentals gpm flow rate total dynamic head tdh head pressure closed loop systems open loop systems glycol systems pump control strategies vfd pumps ecm pumps bas integration pump configuration inline pumps end suction pumps split case pumps redundant pumping lead lag pumps npsh hvac fundamentals industry terms pumps in hvac hydronic pump basics boiler systems hvac pump operation gpm and head pressure ahr boiler Low Water Cut off Air Handler Unit AHU Air Handling Units HVAC Equipment york compressor tp valve temperature and pressure relief valve water heater safety domestic hot water systems plumbing safety devices pressure relief valves thermal expansion protection potable water systems water heater components mechanical code compliance plumbing code requirements boiler vs tp valve hot water storage tanks safety valves facility maintenance boiler relief valves ief electromagnetic flow transmitter optional lcd AI future pressure class gas monitor air quality training certification atrius cloud platform fireye burnlogix yb honeywell q n5 bacnetsc sc niagara fx heating season checklist tc500 promo chart recorder industrial cxc customer center dcv sensor network security cyber ul508a industrial solutions engineering solutions panel assembly custom control panels commercial panels gas regulator sizing gas safety inlet pressure outlet pressure flow rate natural gas propane regulators subnet it managed ip switch vlan setup quality of service qos spanning tree protocol stp routing configuration network management lldp setup energy efficiency ethernet managed network switch benefits ot network energy savings building solutions connected power building management bms transformers din rail transformer functional devices transformer in a box ai in real estate cybersecurity data integration realcomm ibcon sustainability sensors controllers interfaces
Show All

Posts

2026
May April March February January
2025
December November October September August July June May April February January
2024
November October September August July June May April March February January
2023
December November October September August July June May April March
2022