Home comfort depends largely on having proper temperature control throughout your living spaces. When it comes to heating systems, two essential components often confuse homeowners: thermostats and aquastats.
A Thermostat And An Aquastat: Key HVAC Differences
While both serve crucial roles in maintaining comfortable temperatures, they function differently and control separate aspects of your heating system. Understanding these differences can help you make informed decisions about your home’s HVAC setup and know when to call professionals for assistance.
As Mountlake Terrace residents know, reliable heating is essential during the Pacific Northwest’s cool, wet seasons. Let’s explore the key differences between these temperature control devices and when each is needed in your home.
Thermostats: The Air Temperature Controllers
A thermostat is a temperature-sensitive device that regulates the air temperature in your home. It serves as the control center for your heating and cooling system, automatically adjusting operation to maintain your desired indoor temperature.
How Thermostats Work
Thermostats operate on a simple principle: they measure the current air temperature in your home and compare it to your set temperature preference. When the temperature falls below your setting during colder months, the thermostat signals your heating system to activate. Once the desired temperature is reached, it signals the system to shut off.
Modern thermostats come in several varieties:
- Mechanical thermostats: Use physical components like bimetallic strips that expand and contract with temperature changes
- Digital thermostats: Offer precise digital temperature readings and basic programming options
- Programmable thermostats: Allow you to set different temperatures for different times of day
- Smart thermostats: Connect to WiFi networks, learn your preferences, adjust automatically, and can be controlled remotely via smartphone apps
Common Applications
Thermostats are found in virtually every home with a central heating or cooling system. They control:
- Forced-air furnaces
- Central air conditioning systems
- Heat pumps
- Electric baseboard heaters (using specialized thermostats)
- Ductless mini-split systems
Thermostats are typically installed in central locations in the home, away from direct sunlight, drafts, doorways, and room corners to ensure accurate temperature readings.
Aquastats: The Water Temperature Regulators
An aquastat, while less familiar to many homeowners, is equally important in specific heating systems. Unlike thermostats that control air temperature, aquastats monitor and regulate water temperature within heating systems.
How Aquastats Work
Aquastats use temperature sensors to measure the temperature of water in a boiler or hydronic heating system. When water temperature drops below the set point, the aquastat signals the burner to ignite and heat the water. Once the water reaches the desired temperature, the aquastat cuts power to the burner.
Aquastats typically include:
- High limit control: A safety feature that shuts down the boiler if water temperature exceeds a safe maximum
- Low limit control: Maintains minimum water temperature to prevent condensation and corrosion
- Differential setting: Determines how much the temperature can drop before reactivating the burner
Common Applications
Aquastats are primarily found in:
- Hot water boilers
- Hydronic heating systems (radiant floor heating, baseboard hot water heating)
- Indirect water heaters
- Some specialized HVAC applications
Unlike thermostats that are visible on walls in living spaces, aquastats are typically mounted directly on the boiler or water heating equipment and aren’t frequently adjusted by homeowners.
Key Differences Between Thermostats and Aquastats
Understanding the fundamental distinctions between these controllers helps clarify their specific roles in home heating systems:
Medium Controlled
- Thermostats: Monitor and control air temperature in living spaces
- Aquastats: Monitor and control water temperature in heating equipment
Location and Visibility
- Thermostats: Mounted on walls in living areas, easily accessible for adjustment
- Aquastats: Typically installed directly on boilers or water heating equipment, often in basements or utility rooms
System Integration
- Thermostats: Interface with the entire HVAC system, including furnaces, air conditioners, and heat pumps
- Aquastats: Primarily control boiler operation in hydronic heating systems
User Interaction
- Thermostats: Frequently adjusted by homeowners to change comfort levels
- Aquastats: Rarely adjusted after initial setup; primarily service technician settings
Temperature Ranges
- Thermostats: Typically operate in the 60-85°F range for living comfort
- Aquastats: Manage much higher temperatures, often 120-200°F for water systems
This comparison table highlights the major differences:
| Feature | Thermostat | Aquastat |
| Controls | Air temperature | Water temperature |
| Location | Wall-mounted in living spaces | Mounted on boiler/equipment |
| User access | Easily accessible | Limited access |
| Typical range | 60-85°F | 120-200°F |
| Primary systems | Forced air, heat pumps, AC | Boilers, hydronic systems |
When You Need a Thermostat vs. an Aquastat
The type of heating system in your home primarily determines whether you need a thermostat, an aquastat, or both:
You Need a Thermostat When:
- You have a forced-air furnace
- Your home uses a heat pump system
- You have central air conditioning
- You use electric baseboard heaters
- You’ve installed a ductless mini-split system
A properly functioning thermostat ensures your home maintains comfortable temperatures year-round. For Mountlake Terrace homes, where temperatures can vary significantly between seasons, having an accurate, reliable thermostat is essential for both comfort and energy efficiency.
You Need an Aquastat When:
- Your home uses a boiler for heating
- You have a hydronic heating system (hot water baseboard or in-floor radiant)
- Your heating system includes an indirect water heater
- You have a combination heating/domestic hot water system
In the Pacific Northwest’s damp climate, boiler systems provide excellent comfort through radiant heat. The aquastat ensures your boiler operates efficiently while maintaining safe water temperatures.
Systems That Use Both:
Some heating setups employ both controllers working together:
- Hydronic systems with zoned thermostats
- Hybrid heating systems
- Complex HVAC configurations with multiple heating methods
In these cases, thermostats control when heat is delivered to specific zones or rooms, while the aquastat ensures the water in the boiler stays at the proper temperature to deliver that heat effectively.
Maintenance and Troubleshooting
Both thermostats and aquastats can experience issues that affect your heating system’s performance. Knowing the common problems can help you determine when to attempt simple fixes and when to call professionals.
Thermostat Issues and Solutions:
- Inaccurate temperature readings
- Cause: Poor placement, dust accumulation, or sensor failure
- Solution: Clean the interior components, check batteries, or relocate if improperly placed
- System short cycling
- Cause: Improper differential settings or thermostat location
- Solution: Adjust settings or relocate thermostat away from drafts or heat sources
- Unresponsive controls
- Cause: Dead batteries, wiring issues, or component failure
- Solution: Replace batteries, check for loose connections, or replace if necessary
Aquastat Issues and Solutions:
- Boiler overheating
- Cause: Faulty high limit control or sensor problems
- Solution: Professional replacement of aquastat components
- Insufficient heat
- Cause: Incorrect low limit settings or control failure
- Solution: Adjust settings or replace damaged components
- Frequent cycling
- Cause: Improper differential settings
- Solution: Adjust the differential to allow for appropriate temperature swing
For most aquastat issues, professional service is recommended due to the technical nature of boiler systems and safety concerns.
Maintenance Tips for Both Systems:
Regular maintenance helps ensure both thermostats and aquastats function properly:
- Clean thermostat interiors annually to remove dust buildup
- Replace thermostat batteries as recommended by manufacturer
- Schedule annual professional inspection of boiler systems, including aquastat testing
- Keep area around thermostats clear of obstructions
- Monitor system performance for unusual cycling or temperature inconsistencies
When to Upgrade Your Temperature Controls
Technology advances have greatly improved the efficiency and functionality of temperature control systems. Consider upgrading your controls if:
For Thermostats:
- Your current model is over 10 years old
- You want programmable features to save energy
- You’re interested in smart home integration
- Your heating bills seem unnecessarily high
- Temperature varies widely between rooms
For Aquastats:
- Your boiler efficiency seems reduced
- The system cycles too frequently
- You’re updating your boiler system
- You experience inconsistent heating
- You’re adding zones to your hydronic system
Final Thoughts: Making the Right Choice for Your Home
Understanding the difference between thermostats and aquastats helps you make informed decisions about your home’s heating system. While thermostats control the air temperature in your living spaces, aquastats manage the water temperature in boiler systems. Depending on your heating setup, you may need one or both of these essential components.
For Mountlake Terrace homeowners, having properly functioning temperature controls is crucial for maintaining comfort through our variable climate conditions. If you’re experiencing issues with either system or considering an upgrade, consulting with experienced HVAC professionals can help you determine the best solution for your specific needs.
OneStop Heating Cooling Electric has extensive experience with all types of heating systems in the Mountlake Terrace area. Our technicians are fully trained to service, repair, and install both thermostats and aquastats for optimal home comfort. Whether you need a simple replacement or a complete system evaluation, we’re here to help ensure your home stays comfortable in every season.