Replacing a furnace isn’t something most homeowners do often. It’s a long-term investment—one that impacts your comfort, your utility bills, and your home’s resale value. But as simple as it may sound, furnace installation is a complex process with plenty of room for costly mistakes.
Whether you’re upgrading from an older model, switching fuel types, or building from scratch, it pays to understand what can go wrong—and how to prevent it. Here’s a guide to the most common pitfalls during furnace replacement, and how to set your system up for success.
Mistake #1: Choosing the Wrong Size Unit
Bigger is not always better—and smaller isn’t safer. A furnace that’s too large will short-cycle, meaning it turns on and off too frequently. This causes unnecessary wear and makes temperature control inconsistent. On the flip side, a furnace that’s too small won’t be able to keep up in colder months, leading to overwork and underperformance.
Correct sizing involves more than square footage. A qualified HVAC contractor should conduct a Manual J load calculation that considers:
- Insulation levels
- Window size and orientation
- Ceiling height
- Air leakage rates
- Climate zone
Skipping this step is one of the most common mistakes during furnace installation. And it’s one of the easiest to avoid with the right expertise.
Mistake #2: Overlooking Ductwork Condition
Installing a high-efficiency furnace into an old, leaky duct system is like pouring filtered water through a rusted pipe. The air might be warm, but it won’t go where it’s supposed to. Before installation, ductwork should be inspected for:
- Leaks or gaps in connections
- Poor insulation in unconditioned spaces
- Obstructions or debris
- Improper sizing or layout
Airflow is critical to system performance. Without balanced and sealed ducts, even the most advanced furnace won’t deliver on its promise. This is also a key time to look into zoning or airflow improvements, especially if certain rooms in your home are frequently too hot or too cold.
Mistake #3: Ignoring Ventilation and Air Quality
Newer furnace models are highly efficient—but that often means they require updated ventilation systems. Direct-vent or sealed combustion units, for example, pull air from outside the home rather than inside, which improves safety and energy use…