Types, Calculations, and Replacements for HVAC Systems

HVAC Systems: A Comprehensive Guide to Types, Calculations, and Replacement Introduction

Heating, ventilation, and air conditioning (HVAC) systems are invaluable for creating comfortable and healthy indoor environments. But with so many HVAC system types, performing critical calculations, and deciding when to replace aging units, things can get complicated. This guide provides a helpful overview of the most common HVAC system categories, the importance of proper load calculations, and signs it’s time for HVAC replacement.

Central HVAC System Types

Central HVAC systems are designed to heat and cool an entire building from one central unit. The most common central system categories include:

●  Forced Air Systems: These ducted systems use a central furnace and air handler to push heated or cooled air throughout a home or building. Forced air systems include heat pumps, air conditioners, furnaces, and packaged units.

●  Hydronic or Water-Based Systems: Hydronic systems pump heated or chilled water from a central boiler or chiller to terminal units like radiators, fan coils, or in-floor loops. Popular options are boilers with radiators and chillers with fan coils.

●  Geothermal Heat Pumps: Geothermal systems use underground loops filled with water and antifreeze to transfer heat between the earth and a building. A central unit connects to the loops to provide heating, cooling, and hot water.

●  VRF or VRV Systems: Variable refrigerant flow (VRF) and variable refrigerant volume (VRV) are all-in-one central systems that precisely regulate refrigerant flow to multiple air handlers. This provides sim ultaneous heating and cooling.

Room and Zone HVAC Systems

Room and zone HVAC systems heat or cool distinct spaces without ductwork running throughout a building. Common choices include:

●  Window Air Conditioners: These self-contained units mount in windows to cool single rooms during warm weather.

●  Portable Air Conditioners: Freestanding units with ducting kits cool specific rooms without permanent installation.

●  Wall Furnaces: Self-contained gas furnaces provide heating for individual rooms or spaces.

●  Baseboard Heaters: Electric resistance heaters run along walls to heat particular zones.

●  Radiant Floor Heating: Electric or hydronic tubing/cables embedded in floors evenly heat rooms or zones from the ground up.

●  Ductless Mini-Splits: Mini-split systems use an outside compressor to supply refrigerant to one or more wall-mounted evaporators for zone control.

Combination HVAC Systems

Some HVAC systems combine central and zone equipment for optimal comfort and efficiency:

●  Central Gas Furnace with Window AC: Uses central forced-air gas heating paired with room window air conditioning units.

●  Boiler with Baseboards: A central boiler supplies hot water to electric or hydronic baseboard heaters throughout various zones.

●  Air-Conditioning with Electric Heat: A central air conditioner or heat pump provides cooling while electric resistance heaters warm individual spaces.

●  Radiant Floor Heating plus Mini-Splits: Combines in-floor hydronic or electric radiant heat with ductless mini-splits for zone control.

Performing Critical HVAC Load Calculations

Properly sizing an HVAC system is vital for comfort, efficiency, and equipment longevity. HVAC contractors use cooling and heating load calculations to determine the required capacity of HVAC equipment.

Cooling Load Calculation

A cooling load calculation totals the amount of heat that needs removal from a space to maintain desired temperatures. Important factors include:

●  Climate: Outside temperature, humidity, and sun exposure.

●  Building: Insulation, windows, construction materials, tightness.

●  Internal Loads: Occupants, equipment, lighting, processes generating heat.

●  Ventilation: Fresh air requirements.

Cooling load estimates ensure HVAC systems can handle peak conditions without short-cycling or failing to dehumidify effectively.

Heating Load Calculation

Heating load calculation determines how much heat needs supplied to a space to sustain wanted temperatures. Key inputs involve:

●  Climate: Low temperatures, wind velocity, precipitation.

●  Building: Insulation, air leakage, orientation, thermal mass.

●  Internal Loads: Heat from appliances, electronics, lighting, and people.

Accurately calculating heating loads prevents oversized systems that cycle too much while also meeting peak demands.

HVAC Load Calculation Tools

While HVAC professionals can perform load calculations manually, software streamlines the process. Some popular HVAC load calculation tools include:

●  EDS Auditor/Load Calculator: Fast online tools using minimal inputs to produce accurate results through proprietary algorithms.

●  WrightSoft Right-Load Calculations: Robust software for detailed room-by-room load analysis.

●  Elite Software Chvac: Thorough manual-J residential load calculation with optional CAD integrations.

●  Carrier HAP: Trusted program for residential and commercial HVAC load estimation.

Such tools populate inputs based on building data, location, and construction. This automates much of the load calculation process while still allowing manual customization.

Deciding When To Replace HVAC Systems

HVAC units experience wear and tear over years of use. Homeowners and facility managers should consider replacement when:

●  Equipment exceeds typical lifespan estimates: 10-15 years for air conditioners and furnaces, 15-20 for heat pumps and boilers.

●  Energy bills increase despite proper maintenance. Old inefficient systems waste energy.

●  Repair costs mount and parts become difficult to source. It’s often cheaper to replace than perpetually repair.

●  Units short cycle frequently, fail to maintain comfortable temperatures, or operate for long periods without turning off. This signals undersized or failing equipment.

●  Inspection reveals corrosion, cracks, leaks, odors, or dangerous combustion byproducts like carbon monoxide. Serious damage risks failure.

●  Upgrading enables access to new smart technology, improved comfort, and increased energy savings.

While systems may keep functioning past expected lifespans, replacement often proves the wiser investment long-term.

HVAC Replacement Process

Replacing HVAC equipment is a major undertaking requiring research and expertise. Key steps include:

  1. Inspect and diagnose current system issues.
  2. Research new system options, costs, efficiency ratings, and incentives/rebates.
  3. Calculate cooling and heating loads for proper new equipment sizing.
  4. Obtain multiple quotes from qualified, licensed HVAC installation contractors.
  5. Choose new efficient system meeting calculated loads and budgets.
  6. Schedule install when heat/cooling demands are lower.
  7. Verify proper permitting, installation, and functionality after the install.
  8. Consider enhanced controls, zoning, and ductwork upgrades for maximum performance.
  9. Budget for repairs or replacements of complementary systems like furnaces/ACs, ductwork, or piping. 

With smart planning and preparation, HVAC system replacement can significantly bolster year-round comfort, air quality, and energy savings.

Related Article: Unveiling the Science Behind HVAC Load Calculation: Achieving Precision with EDS Heat Load Calculator


From forced-air furnaces to boilers and mini-split systems, today’s HVAC options offer solutions tailored to buildings’ needs. But capitalizing on their benefits requires accurate load calculations for ideal sizing plus knowing when aging equipment necessitates replacement. This helps create indoor environments that are cozy, breathable, and energy efficient across the seasons. With this HVAC knowledge, building owners can make informed equipment selections that provide comfort and savings for years to come.