Furnace Installation: Gas vs Electric and Sizing Guide

Choosing a new furnace isn’t just about picking a brand and hoping for the best. The type of furnace you choose—and making sure it’s sized correctly—directly impacts how comfortable your home will be, how much you’ll pay in energy bills, and how long the system will last. Get it wrong, and you could face 15-20 years of higher bills, uneven temperatures, or a system that wears out before its time.

This guide covers everything you need to know about gas vs. electric furnaces, plus how to make sure you’re getting the right size for your home.

How Gas Furnaces Work

A gas furnace heats your home through combustion. Natural gas flows into the unit where a burner ignites it, creating hot combustion gases that pass through a metal component called the heat exchanger. Air from your home flows over this exchanger, absorbs the heat, and a blower motor pushes that warmed air through your ductwork and into every room.

The combustion process produces exhaust gases—including carbon monoxide—that must be safely vented outside. Standard-efficiency furnaces vent through a metal chimney flue, while high-efficiency models use PVC pipes that exit through a wall. This venting requirement is why gas furnace installation involves more steps than electric, but the tradeoff is significantly lower operating costs in most areas.

Gas furnace efficiency is measured by AFUE (Annual Fuel Utilization Efficiency), which tells you what percentage of the fuel actually becomes heat for your home. An 80% AFUE furnace converts 80 cents of every dollar spent on gas into usable heat—the other 20 cents goes up the flue. High-efficiency models rated 90-95% AFUE waste far less, and premium condensing furnaces can reach up to 98% AFUE by extracting additional heat from exhaust gases that standard furnaces vent away.

For Richmond homeowners with existing natural gas service, gas furnaces offer powerful heating that works efficiently even on the coldest days. Natural gas typically costs less than electricity per unit of heat produced, which translates to lower monthly bills throughout the heating season.

How Electric Furnaces Work

Electric furnaces generate heat through resistance coils—essentially working like a large toaster. Electricity passes through heating elements that warm up, and a blower fan pushes air across these hot coils and distributes it through your ductwork. There’s no combustion involved, no gas lines required, and no venting needed since the system produces no exhaust.

This simpler design makes electric furnaces easier and often cheaper to install. They also come with fewer safety concerns—no gas leaks, no carbon monoxide production, and no annual combustion inspections required. Maintenance typically involves filter changes, occasional coil cleaning, and checking electrical connections.

Electric furnaces convert nearly 100% of the electricity they consume into heat. No energy escapes through a flue because there isn’t one. On paper, that sounds more efficient than even the best gas furnace—so why do electric furnaces cost more to operate?

The answer comes down to fuel prices. In Virginia and most of the country, electricity costs significantly more per unit of energy than natural gas. Even though an electric furnace wastes almost nothing in conversion, you’re paying more for the energy it consumes. The math works out to higher monthly heating bills in most situations, particularly in areas with cold winters where the furnace runs frequently.

Electric furnaces can make sense when a home doesn’t have natural gas service available, when the cost of running a gas line is prohibitive, or in milder climates where heating demands are minimal. They also last longer on average—20 to 30 years compared to 15 to 20 for gas—because fewer moving parts and no combustion means less wear over time.

Gas vs Electric—Comparing the Real Differences

For most Richmond homeowners, gas furnaces are the more cost-effective choice for day-to-day operation. Natural gas prices have remained lower than electricity rates, and that gap typically makes gas the winner on monthly heating bills even when you factor in the efficiency differences. That said, the right choice depends on your specific situation.

Upfront costs favor electric furnaces. The equipment itself costs less, and installation is simpler without gas line connections and venting requirements. If your home already has natural gas service and proper venting, the installation cost difference narrows considerably. If you’d need to run a new gas line to your home, electric may be the more practical option despite higher operating costs.

Operating costs favor gas furnaces in most cases. Natural gas furnaces have achieved excellent efficiency ratings—90% AFUE and higher is now common—and natural gas prices tend to be more stable than electricity rates. Virginia homeowners typically see lower monthly heating bills with gas, particularly during cold stretches when the furnace runs frequently.

Lifespan and maintenance present a tradeoff. Gas furnaces last 15 to 20 years with proper care, while electric furnaces can run 20 to 30 years. However, gas furnaces require annual safety inspections to check for cracked heat exchangers and carbon monoxide risks. Electric furnaces need less specialized maintenance, though they still benefit from yearly professional tune-ups to ensure electrical connections are secure and components are working properly.

Safety considerations differ significantly. Gas furnaces involve combustion and require proper venting to prevent carbon monoxide from entering your home. A cracked heat exchanger—though uncommon with regular maintenance—can allow exhaust gases to mix with your home’s air. That’s why carbon monoxide detectors are essential in any home with gas appliances. Electric furnaces eliminate these combustion-related risks entirely, though they still require proper electrical installation and grounding.

Not sure which fuel type makes sense for your home? We’ll look at your current setup and give you an honest recommendation—not a sales pitch.

Why Furnace Sizing Matters More Than You Think

Getting the right size furnace is just as important as choosing between gas and electric—maybe more so. An improperly sized furnace will cause problems regardless of how efficient or expensive it is. And the most common mistake isn’t going too small; it’s going too big.

An oversized furnace heats your home too quickly. That sounds like a good thing until you understand what happens next. The furnace blasts on, floods your home with heat, and the thermostat satisfies almost immediately. Then it shuts off. A few minutes later, temperatures drop, and the cycle repeats. This short cycling creates several problems: rooms near the thermostat get too hot while distant rooms never fully warm up, humidity isn’t properly controlled because the system doesn’t run long enough, and the constant on-off cycling puts stress on components that leads to premature wear. An oversized furnace can waste 20-35% more energy than a properly sized unit and may fail years before its time.

An undersized furnace can’t keep up on the coldest days. It runs constantly, struggling to reach your thermostat setting, which drives up energy bills without delivering comfort. Extended run times accelerate wear on the blower motor and other components. Your home may feel perpetually chilly during cold snaps, and the system may never satisfy the thermostat during extreme weather.

The “bigger is better” mentality causes problems in HVAC more than almost any other industry. A furnace that’s slightly undersized will actually perform better than one that’s oversized—on most days it will cycle normally and efficiently, and on the few coldest days of the year, it simply runs a bit longer. Many properly sized furnaces run almost continuously on the coldest day of the year, and that’s exactly how they’re designed to work.

How can you tell if your current furnace is the wrong size? Look for these signs: the system turns on and off every few minutes (short cycling), some rooms are always too hot while others stay cold, your energy bills seem unusually high, or the furnace runs constantly but can’t maintain temperature during cold weather.

How We Determine the Right Size for Your Home

Proper furnace sizing requires a Manual J load calculation—the industry standard developed by the Air Conditioning Contractors of America. This isn’t guesswork, and it’s not a formula based solely on square footage. It’s a detailed analysis of how much heat your specific home loses on the coldest expected day of the year.

Manual J calculations account for your home’s square footage, but also ceiling heights (higher ceilings mean more volume to heat), insulation levels in walls, attic, and floors, the number, size, and efficiency of windows, the direction your home faces and sun exposure, air infiltration from drafts and building tightness, and local climate data for Richmond’s typical winter temperatures.

A 2,000-square-foot home built in the 1970s with original windows needs a completely different furnace than a 2,000-square-foot home built in 2015 with modern insulation and low-E windows. Rules of thumb like “30 BTU per square foot” ignore everything that actually matters about heat loss.

Why can’t you just match your old furnace size? Because your old furnace may have been sized incorrectly to begin with—studies suggest roughly half of all HVAC systems are improperly sized. Your home may have changed through upgrades like new windows, added insulation, or finished spaces. And older furnaces often had lower efficiency ratings, meaning a modern high-efficiency unit produces more usable heat from the same rated capacity.

A proper sizing assessment takes time—we measure rooms, inspect insulation, evaluate windows, and run the calculations. It adds maybe 30 minutes to an estimate visit, but it’s the difference between a system that works perfectly for 15-20 years and one that creates problems from day one.

What to Expect During Furnace Installation

Furnace installation typically takes 4 to 8 hours for a straightforward replacement. More complex situations—ductwork modifications, switching from electric to gas, or difficult access—can extend that timeline.

The process begins before installation day. During your consultation, we assess your home’s heating needs, measure spaces, inspect your ductwork, and perform load calculations. By installation day, we know exactly what equipment you need and have it ready.

On installation day, the crew starts by protecting your home—laying drop cloths, covering furniture near work areas, and ensuring a clean workspace. The old furnace is disconnected from electrical, gas (if applicable), and ductwork, then carefully removed. For gas-to-gas replacements, this takes 1-2 hours.

With the old unit out, technicians prepare the installation site. They inspect the surrounding area, check for any ductwork issues, and make sure the new unit will fit properly. The new furnace is positioned, leveled, and secured. Ductwork connections are made and sealed, gas lines are connected (for gas furnaces), and electrical wiring is completed.

What happens next separates quality installation from average work: thorough testing and commissioning. This isn’t just flipping the switch to see if it turns on. Proper commissioning includes checking gas pressure and burner operation, measuring airflow and static pressure in the duct system, verifying temperature rise matches specifications, testing safety controls and limits, calibrating the thermostat, and ensuring carbon monoxide levels are safe. This testing can take an hour or more but ensures your system operates at peak efficiency from day one.

The visit ends with a walkthrough. We explain how to operate your new system, show you where filters are located and how to change them, review warranty information, and answer any questions. You’ll know exactly how to get the most from your investment.

Making the Right Choice for Your Home

The right furnace—properly sized and correctly installed—will keep your family warm for 15-20 years without wasting money or causing headaches. The wrong one creates problems that compound over time: higher bills, uneven comfort, frequent repairs, and early replacement.

At H&H Heating and Air Conditioning, we take the time to calculate exactly what your home needs and explain your options clearly. Our technicians don’t work on commission, which means the recommendation you get is based on what’s right for your home—not what’s most profitable for us. With over 50 years serving Richmond, NATE certification, an A+ BBB rating, and our Price Match Guarantee, we’re here to help you make the right decision.

Ready to find the right furnace for your home? Schedule a free consultation and we’ll walk you through your options—gas or electric, sized exactly right.

Frequently Asked Questions