What is a "Condensing" Furnace? (And Why You Probably Want One)

If you are shopping for a new furnace, you will see two main categories: "Standard Efficiency" (80%) and "High Efficiency" (90% to 98%). High-efficiency models are often called Condensing Furnaces.

To the average homeowner, that name sounds a bit like a science experiment. Why would a furnace "condense"? Doesn't that mean water? And isn't water bad for a furnace?

Here is the simple explanation of how this technology works and why it is the gold standard for heating homes in the Treasure Valley.

The Old Way: Throwing Heat Away (80% Efficiency)

In a standard 80% efficiency furnace, the process is simple:

1. Gas burns to create heat.
2. Fans blow that heat into your home.
3. The exhaust gases (which are still very hot) are vented up your chimney and out the roof.

The New Way: Squeezing the Sponge (90%+ Efficiency)

A Condensing Furnace is designed to capture that wasted heat.

It has two heat exchangers instead of one:

• Primary Exchanger: Does the same job as a standard furnace—heats the air.
• Secondary Exchanger: This is the game-changer. It takes the hot exhaust gases and runs them through a second set of coils. It squeezes the remaining heat out of that exhaust until the gas cools down significantly.

The Result: You keep 96 to 98 cents of every dollar you spend on heating.

How to Spot a Condensing Furnace

You can tell if a home has a high-efficiency furnace just by looking at the venting.

• Standard Furnace: Uses a metal "chimney" pipe (flue) going up through the roof. Due to the cold temperature of attics in Idaho, these often corrode due to gases cooling down before leaving the end of the vent. This corrosion falls back into the furnace exhaust motor, leading to blockages and failures.
• Condensing Furnace: Uses white PVC plastic pipes. Because the exhaust is so cool, it doesn't need a metal chimney. It can be vented right out the side of the house using simple plastic piping.

The Benefits for Idaho Homeowners

1. Massive Energy Savings

In a climate like ours, where the furnace runs for 5–6 months of the year, jumping from 80% to 96% efficiency can save you hundreds of dollars annually. The system pays for itself over time in gas savings alone. This is one of the few home efficiency upgrades that actually pays off.

2. Variable Speed Availability

These furnaces can be upgraded to true variable speed. With modulating gas valves and variable speed blow motors, these furnaces can deliver exactly the amount of heat your home needs to stay comfortable. The days of massive temperature swings waking you up at night can be over.

3. Sealed Combustion (Safer & Cleaner)

Most condensing furnaces draw their intake air from outside the home (via a second PVC pipe).

• Standard furnaces burn the air inside your home (the air you already paid to heat!).
• Condensing furnaces are sealed systems. They don't dry out your indoor air, and they eliminate the risk of back-drafting carbon monoxide into your living space.

4. Quieter Operation

Because they are built with heavier cabinets and often feature sealed combustion, these units tend to operate much more quietly than the roaring furnaces of the past.

Is It Worth the Upgrade?

For most homes in Meridian and Boise, the answer is Yes. The long-term fuel savings and the increased home resale value make it a smart investment.

However, installation can be more complex because we have to install new venting (PVC pipes) and a drain line for the water. We can assess your home to make sure the upgrade is feasible.