Heating a House – High Efficiency Furnace Systems

Heating a House with a High Efficiency Furnace

What’s the Best Furnace for Heating a House?

Your furnace is the heart of your HVAC system and heating a house takes energy. Furnaces combust a fuel source to heat air and blow that air through ductwork to warm the rooms in your home. Like any appliance, a furnace’s efficiency rating measures the ability to convert energy to heat over the course of a typical year. The AFUE, or annual fuel efficiency, measures this conversion. 

You might think that high efficiency is better and more economical than lower efficiency. The answer is, “Yes, but only when taken in context of other components and house conditions.”

There are a number of considerations that go into determining the best furnace to heat your home. If you’re building a new home, replacing an old furnace, or thinking of buying a home with an existing furnace and you want to figure out what the annual cost might be to operate it heat your house, there are a few things to consider. 

Keep in mind that the least expensive furnace can easily cost you more over the long run. Lower priced units are likely less efficient, which means they cost more to operate. And, in many cases, they cost more to maintain and repair. They also don’t do a great job of heating a house.

Ongaro and Sons have generations of experience with installing, maintaining and repairing furnaces. Here’s what consumers need to know about furnaces and furnace efficiencies:

  • Types of furnaces
  • What are the different levels of efficiency 
  • The relationship between furnace efficiency, ductwork and attic insulation
  • How to make the best decision on furnace efficiency for your home and HVAC system

Types of Furnaces to Heat a House

Different furnace types can be distinguished by the fuel source they use:

  • Natural gas
  • Oil
  • Electric
  • Propane

There are also dual fuel furnaces that use a heat pump and typically have a gas back up. Heat pumps draw warmth from outdoors which passes over a coil of hot refrigerant; a fan blows the warmed air through the home to heat the house. During colder months the furnace employs a more traditional gas backup when there is insufficient heat from outside air to maintain comfortable temperatures indoors.

Furnaces are not only distinguished by the type of fuel they use, but also their efficiency rating. Oil furnaces are less efficient than natural gas, but the upfront purchase costs are also less expensive than gas. Of course, your furnace fuel source is largely dependent on what your utility supplies. Propane, stored in a tank, is another option if gas or oil isn’t available. Propane can help you avoid the increasing cost of electricity (though electric furnaces cost roughly half that of gas furnaces and usually have high efficiency ratings).

Regardless of fuel source, furnace efficiency ratings are somewhat useful for shopping comparisons, at least to start. Let’s begin by defining what furnace efficiency actually means.

The efficiency rating states the amount of gas consumption out of 100 percent used for heating a house based on the design of your furnace. If a manufacturer claims its furnace has an 80 percent efficiency rating, that means the furnace uses 80 percent of the fuel to heat for heating a house. Which also means your combustion flue exhausts 20 percent of the gas consumed. 

What does that mean in terms of dollars and cents? For every dollar you spend on furnace fuel consumption, you spend 80 cents on heating a house and 20 cents literally goes up and out the chimney. 

Generally speaking, furnaces are divided into high efficiency, mid or standard efficiency and low efficiency. What’s the difference?

  • High Efficiency: Manufacturers define a high efficient furnace as an efficiency rating of at least 90 percent. Most newer high efficient furnaces today start at 95 percent. 
  • Mid (or Standard) Efficiency: A manufacturer efficiency rating of at least 80 percent. This is considered the minimum efficiency standard for any central heating system.
  • Low Efficiency: Furnaces below the minimum standard include wall furnaces, floor furnaces and direct vent furnaces. The efficiency rating of these furnaces can range from 50 to 80 percent.

The efficiency rating also depends on how the furnace operates, whether you have a single- stage, two-stage, multi-stage or modulating system. 

  • Single Stage: A single stage furnace turns on 100 percent completely when calling for heating and shuts off when it achieves temperature. This cycle repeats every time the thermostat calls for heating. 
  • Two Stage: In the first stage, the furnace works at 60 percent capacity; at the second stage it works at 100 percent capacity. These are slightly more efficient than single stage units but the advantage here is comfort (the system is quieter, uses less energy and runs longer. Allowing it to stay off, longer). Two stage equipment also usually features variable speed motors to help improve indoor air quality. Both high and standard efficiency systems come in two stage models. This is a great application for dual-zoned homes. 
  • Modulating/Multi-stage: These models are specific to high efficiency furnace models only. Modulating or multi-stage systems have the capacity to work in successive degrees from as low as 40 percent capacity up to 100 percent capacity. Some systems can have upwards of 100 stages. These systems are great for multi-zoned home HVAC applications. Multi-stage systems “communicate.” A wall mount thermostat control communicates data to the system to allow it to t efficiently operate on its own without user direction to meet typical demand and temperature requirements. These communicating systems are great if you like to “set it and forget it.”

Note that the efficiency rating is a manufacturer’s definition. Your furnace may not actually achieve that efficiency. Why? 

Efficiency testing in a controlled environment determines efficiency ratings. But this environment likely doesn’t replicate your daily living conditions. It’s similar to auto fuel ratings. Whether a car can actually achieve its 35 mile per gallon highway rating depends on how you drive and under what conditions you have to drive. Individual mileage is going to vary.

What conditions determine if your furnace can run at maximum efficiency? Ductwork and attic insulation play a big role.

Furnace Efficiency, Ductwork and Attic Insulation

For your furnace to achieve maximum efficiency, the size of your ductwork needs to match your furnace. Ductwork comprises the tubes that distribute conditioned air throughout your house. For the most part concealed ductwork is found behind walls and underneath floors; ductwork is only readily accessible in crawl spaces, basements and exposed attic ceilings. 

The ductwork must be able to deliver the right CFM (cubic feet per minute) of airflow with the factory specified static pressure for both air coming in and air going out of your furnace to heat with maximum efficiency. Ensuring correctly designed ductwork is important, as it needs to  shut off or open correctly when rooms in your house call for heat.

If you’re building a house and installing a completely new HVAC system, the contractor should size the ductwork for the appropriate furnace. If you’re replacing a furnace, you need a flow hood test of the ductwork. This not only tells you if the ductwork can work efficiently with a planned new furnace, but also if your ductwork has any leaks that are going to impede efficiency if left unrepaired.

Another thing to look at is your attic insulation. Proper insulation keeps the heat out during the summer and the cold out during the winter. It is the only thing in your home working 24/7 365 days a year to save you money. You can buy the best equipment money can get, but if your house is not insulated you’ll never achieve the comfort you desire and money that you could possibly save is literally going up and out of your roof.

Other factors that go into determining furnace efficiency and what is best for your situation include:

  • The size of your home and living space
  • Local climate conditions
  • Room ceiling heights
  • Number of windows

How to Make the Best Decision on Furnace Efficiency to Heat Your House

You may find all this talk about CFM and AFUE a bit confusing. That’s understandable. It always helps to have some knowledge to make a decision on big purchase items like furnaces. It also helps to have the advice of professionals trained and certified in the installation of furnaces and HVAC systems.

Professionally trained Ongaro and Sons technicians work with all residential makes and models of furnaces and HVAC systems. We are happy to advise you on what can work best for the needs in your home. All of our furnaces come with a 10 year parts and labor warranty.

All our work is guaranteed and performed at the price we quote. If you are considering a new furnace, either for new house construction or to replace an old furnace, contact Ongaro and Sons for a consultation and free estimate.