Single-Stage vs Two-Stage Furnace in Boise

August 30, 2019

If you’re looking for a new furnace, you may have heard about furnace stages. And you may be wondering if you should go with a single- or two-stage furnace.

Here’s our general recommendation:

  • If you’re on a tight budget, stick with a single-stage furnace
  • If you want a higher level of comfort and you can afford the higher upfront install cost, go with a two-stage furnace

We’ll explain this recommendation in more detail below. But first, we’ll give you a quick refresher on what furnace stages are.

Want a recommendation for your new furnace? The best way to get an accurate recommendation is to contact an HVAC professional. We can help!

What are furnace stages?

Stages refer to the type of fuel valve included in a furnace’s burner system.

A standard, single-stage furnace has a simple fuel valve. When the valve is open, fuel travels through the valve to the pilot light. Once the fuel hits the pilot light, it ignites and burns inside the burner section of your furnace.

Essentially, when a single-stage furnace is on, it runs at 100% capacity—no matter what. The problem is that when your home needs just a little heat, the furnace turns on full blast and warms your home quickly. This is not very energy-efficient, and it can lead to indoor air quality and temperature issues (more on that below).

On the other hand, a two-stage furnace has a more advanced valve. This valve has 3 positions: open, partially open and closed. These positions give the furnace a “high,” “low” and “off” setting. That means the furnace can run at 100% capacity (high) or 60% capacity (low), depending on how much heat is needed.

The additional speed gives a two-stage furnace several advantages over a single-stage furnace. These advantages include:

  • Cheaper operational costs: Since a two-stage furnace can run on a “low” setting, it consumes less energy than a single-stage furnace. This means a two-stage furnace can potentially save you money on your energy bills every month. 
  • Improved comfort: Because two-stage furnaces don’t blast heat into your home all the time, they run longer. The longer a furnace runs, the more it can circulate warm air throughout a room, which eliminates hot/cold spots.
  • Better indoor air quality: Similar to the point above, a two-stage furnace runs longer (without raising costs), which gives your furnace filter a chance to remove more pollutants from the air.
  • Longer equipment life: The less your furnace has to go from 100% heating capacity to 0% capacity, the less wear and tear it will experience. Two-stage systems reduce the strain on your furnace equipment by offering a low capacity heating option.
  • Quieter operation: Often, two-stage furnaces come with a two-speed or multi-speed blower motor, which give the furnace a low-speed option. Lower fan speeds = reduced noise.

Is a two-stage furnace worth the higher installation price?

Because we rely heavily on our furnaces in Boise, we usually recommend going with a two-stage system.

However, two-stage furnaces are more expensive (typically $500 to $1,000 more) to install than a single-stage furnace.

If you’re concerned about whether or not a two-stage furnace is worth the higher investment, speak with an HVAC professional. They can help you weigh the pros and cons and see if a two-stage furnace makes sense for your home and budget.

Note: If you want the highest level of comfort and energy-efficiency, you can ask your furnace contractor about multi-stage/modulating furnaces. These furnaces offer more stages than a two-stage furnace, which gives you even more comfort and heating control. If you’re interested, you can ask your furnace contractor if this type of furnace would be a good option for you.

Want a furnace recommendation from a Boise HVAC pro?


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