The Complete HVAC Replacement & Sizing Guide

Replacing or upgrading your HVAC system is a major decision. Between system sizing, installation cost, efficiency ratings, refrigerant changes, and deciding between central air or ductless mini splits, it’s easy to get overwhelmed.

At MRCOOL DIY Direct, we operate as both a nationwide MRCOOL retailer and a division of a local HVAC business. We work daily with leading HVAC brands including Daikin, Goodman, Amana, GWIN, and MRCOOL. That means we approach system selection from a contractor’s perspective—not just an online seller’s.

This guide will help you understand HVAC replacement costs, system sizing, BTU requirements, installation considerations, and how to choose between central ducted and ductless systems.

How Much Does HVAC Replacement Cost?

The cost to replace an HVAC system depends on system type, tonnage or BTU capacity, efficiency rating, refrigerant platform, ductwork condition, and regional labor rates.

Central ducted system replacements typically range from mid four figures to low five figures installed, depending on complexity and size. Ductless mini split systems generally have lower installed costs for single-zone systems and scale based on multi-zone configurations.

DIY-ready systems can reduce labor costs significantly when properly installed, since much of the expense in traditional HVAC replacement comes from labor rather than equipment.

For a full breakdown of equipment vs. labor costs and what drives pricing up or down, see our detailed HVAC Replacement Cost guide.

How to Properly Size an HVAC System

Improper sizing is one of the most common HVAC mistakes. A system that is too small may run constantly and struggle during extreme weather. A system that is too large may short cycle, reduce humidity control, and lower overall efficiency.

One ton of cooling equals 12,000 BTUs per hour. Residential central systems commonly range from 1.5 to 5 tons. Mini split systems typically range from 6,000 BTU to 36,000 BTU per indoor unit.

Square footage alone is not enough to determine proper sizing. Accurate sizing should consider climate zone, insulation quality, window exposure, ceiling height, air leakage, and overall home layout. A Manual J load calculation provides the most accurate sizing method.

For deeper guidance, review our complete HVAC Sizing Guide.

Central Ducted vs. Mini Split Systems

Central ducted systems are ideal for homes with existing ductwork and provide whole-home uniform temperature control. These systems are commonly available from 1.5 to 5 tons and are offered in Good, Better, and Best tiers depending on efficiency and performance features.

Ductless mini split systems are ideal for homes without ductwork, additions, garages, workshops, and zoned applications. Modern 5th Generation systems include inverter-driven compressors, ENERGY STAR options, and refrigerant platforms such as R-454B for improved efficiency and rebate eligibility.

Mini splits allow independent temperature control by zone, which can reduce energy waste compared to traditional single-zone ducted systems.

For a deeper comparison, review our Mini Split vs. Central Air guide.

DIY vs. Professional Installation

DIY-friendly HVAC systems are engineered to simplify installation through features like pre-charged condensers, pre-charged line sets, and Quick Connect fittings. These designs reduce installation complexity for capable homeowners.

However, electrical panel capacity, local code requirements, permit requirements, and overall project complexity should always be considered. Many homeowners choose a hybrid approach, installing mechanical components themselves while hiring a licensed electrician for final electrical connections.

Choosing the Right HVAC System for Your Home

Before selecting a system, consider your square footage, climate zone, ductwork condition, desired zoning control, and available rebates in your area.

A properly sized and correctly installed HVAC system will improve comfort, reduce energy consumption, and extend equipment lifespan.

Explore our available systems to compare 5th Generation DIY mini splits, central ducted heat pump systems, and Hyper Heat models designed for colder climates.

Frequently Asked Questions

How do I know what size HVAC system I need?

Start with square footage, then adjust for insulation, climate zone, ceiling height, and home layout. A Manual J load calculation provides the most accurate sizing results.

Is a 2-ton AC enough for my home?

A 2-ton system (24,000 BTU) may be appropriate for well-insulated homes around 1,000–1,200 square feet depending on climate. Always verify sizing factors before purchase.

Are DIY HVAC systems reliable?

When properly sized and installed according to manufacturer guidelines, modern DIY-friendly systems are engineered for long-term reliability and performance.

Is a mini split more efficient than central air?

In many zoned applications, mini splits can be more efficient because they allow conditioning of only occupied spaces rather than the entire home.