modulating gas furnace vs two-stage furnaceModulating Gas Furnaces - Gas furnace manufacturers have for many years been working on modulating furnaces to make furnaces more efficient. Before modulating furnaces, the highest rated (efficiency-wise) were two-stage gas furnaces. Then came the modulating furnaces.

Efficiency ranges started increasing to 98% and fractionally more than 98% for some modulating gas furnaces. Always check the AHRI website for the certified efficiency of any HVAC product you purchase. What makes this furnace different than the other types of gas furnaces you can purchase?

Modulating gas furnaces are also condensing gas furnaces. All-natural gas and propane gas has a small percentage of moisture in the gas. When the combustion process takes place the moisture in the gas turns into steam. A condensing gas furnace has two heat exchangers.

In the secondary heat exchanger, any residual heat is absorbed into the exchanger, and the air passing around the exchanger. This maximizes the amount of heat used by the furnace. It also makes it far more efficient than a non-condensing gas furnace. That moisture is then drained down the same drain the air conditioner uses. The moisture produced by the evaporator coil.

Modulating Gas Furnaces

A modulating furnace will operate incrementally in a range from 40% all the way up to 100%. The increments for some manufacturers is 1% which offers a good demand-based furnace. This range depends on demand. Therefore, for the modulating furnace to operate properly the controls need to be set up properly. In many cases, the controls including the thermostat are proprietary.

You will need the manufacturer of the furnace to provide the thermostat. Other gas furnaces such as the two-stage gas furnace only offer two stages. Consequently, the stage from 50% and 100% depends on the manufacturer and furnace set up.

Modulating Gas Furnaces - condensing gas furnace
Some manufacturers will program their modulating furnace to operate on a conventional single-stage or two-stage thermostat. In that case, rather than getting the furnace to modulate incrementally, the furnace will stage. It will stage to certain percentages based on the type of thermostat used.

A single-stage thermostat will offer less staging than a two-stage thermostat. In either case, it allows you to have a more efficient furnace. More efficient than just a single-stage or even a two-stage furnace.

Comparisons | Modulating Furnaces - Gas Furnace Purchase Options

The two-stage gas furnace is more efficient than the single-stage gas furnace which only operates at 100%. The cost also varies from the furnace to furnace with the modulating gas furnace costing more than the other two. In many cases a lot more so it is important to compare the cost.

The cost of the furnace plus operating expenses and figure out the payback or ROI for buying efficiently. Living in the house for a long period of time? Then it is better in most cases to purchase the most efficiently.

However, if you sell the home a new efficient HVAC system will add value to the home. It will definitely be a plus for the buyer and possibly help you sell faster for a better price.

Benefits of a Modulating Gas Furnace

The overall benefits of having a modulating gas furnace over the other types of gas furnaces have some comparisons that are demonstrable. First, the efficiency of modulating over two-stage and single-stage is the biggest factor because it not only saves you money it saves energy. This causes less pollution. I’m a big promoter of energy savings so I will, given the right factors, encourage people to purchase the most efficient product.

As stated previously, it’s a good thing for them in the resale value of the home and other areas including saving money and energy. Another demonstrable area that a modulating gas furnace has that is beneficial over other gas furnaces is temperature swing. As you can see from the graph below the temperature swings are much less pronounced over two-stage and single-stage gas furnaces.

Modulating Gas Furnace Vs Two-Stage Gas Furnace

While, in the graph below, you see a distinguishable difference in the temperature, the modulating gas furnace is superior to the two-stage gas furnace. This is simply another reason to purchase a modulating gas furnace over a two-stage gas furnace provided the following conditions are met:

  • The installation contractor is very skilled and knows what they are doing in the installation. It is very important that these furnaces are installed properly. You can buy the most efficient gas furnace in the world but if it is not installed properly you won’t see the efficiency or the savings. The competency of the contractor is the number one reason I recommend over any brand or type of system you can purchase.
  • Ancillary systems such as the ductwork and proper home insulation (tightness) are good. Again, what good is it to install a super-charged state-of-the-art engine in an AMC Pacer when it needs to go in a Formula One race car? If you have leaking ductwork and drafty windows an energy-saving nor will a comfort level be realized with the higher efficiency model?

modulating gas furnace benefits comparison chart

Conclusion | Modulating Gas Furnaces - Furnace Purchase Options

When you purchase expensive equipment it is important that a certified HVAC contractor install the equipment. The higher-end HVAC equipment usually comes with bells and whistles. The final start-up is important so that you get the properly rated efficiency out of the equipment. Additionally, I always recommend that you purchase an extended warranty that includes labor. The parts are expensive and the troubleshooting can often take longer because these systems are complex.

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Modulating Gas Furnaces - Furnace Purchase Options

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