Installing a new furnace is a big step—whether you’re replacing an older heater that’s on its last leg or outfitting a new home build in the San Antonio, TX area. Done right, a furnace installation should deliver years of reliable, safe, and efficient heat. Done wrong, it can lead to comfort problems, higher utility bills, frequent breakdowns, and (in the case of gas furnaces) serious safety risks.

At Cowboys Air Conditioning & Heating (Cowboys AC), we install and replace heating systems for homeowners throughout San Antonio and nearby communities like Selma, Live Oak, Universal City, Schertz, Cibolo, Converse, Windcrest, Kirby, Leon Valley, Castle Hills, Alamo Heights, Stone Oak, Boerne, and Bulverde—and we’ve seen the same preventable furnace-install mistakes come up again and again. Cowboys AC’s team emphasizes safe, code-compliant workmanship and installs a full range of heating options, including gas furnaces, electric furnaces, heat pumps, ductless mini-splits with heat, and dual fuel systems.

Below are the most common furnace installation mistakes—and the simple way to avoid them.

Mistake 1: Installing the Wrong Size Furnace

A furnace can be too small or too large for the home—and both cause problems.

If the furnace is undersized:

• It may struggle to reach the set temperature

• It runs longer and harder (higher energy use)

• It can wear out faster due to constant operation

If the furnace is oversized:

• It may “short-cycle” (turn on/off repeatedly)

• Temperature can swing up and down

• Humidity and comfort may suffer (especially in shoulder seasons)

• Components can fail early from repeated starts

Proper sizing isn’t guesswork. It should be based on the home’s heating load (square footage is only one piece of the puzzle), plus insulation levels, window efficiency, duct design, and how the home handles airflow.

Cowboys AC highlights the importance of professional installation by trained technicians and positions its installs around best practices and code-compliant work.

Mistake 2: Sloppy Duct Connections (or Ignoring Duct Problems)

Even the best furnace can’t perform well if the duct system is leaking, poorly designed, or improperly connected. This is especially common when homeowners replace equipment but keep old ductwork that was never updated.

Common duct-related installation issues include:

• Loose connections at the supply plenum or return

• Duct leaks in attics or crawl spaces

• Poorly sealed joints that bleed heated air into unconditioned spaces

• Return-air problems that choke airflow and create hot/cold spots

In older neighborhoods around San Antonio—and in areas like Selma and Schertz where homes have expanded quickly—duct layouts aren’t always ideal. A quality installation should include checking static pressure, confirming proper return airflow, and sealing/repairing ducts as needed so the new system can actually deliver the comfort you’re paying for.

Mistake 3: Poor Ventilation and Combustion Safety (Gas Furnaces)

If you’re installing a gas furnace, ventilation must be done correctly. The combustion process creates exhaust gases that must be vented safely outside. A poorly designed or incorrectly sized flue, bad draft, or improper termination can create dangerous conditions.

One of the key reasons ventilation matters is carbon monoxide safety. Furnaces generate hot exhaust gases that must be carried out through a flue or venting system so harmful gases don’t build up inside the home.

Ventilation/combustion mistakes can include:

• Improper flue sizing

• Faulty vent connections

• Incorrect pitch or routing

• Using the wrong vent material for the application

• Poor placement that leads to backdrafting

This is where “cheap installs” get expensive fast. You want a team that understands Texas code requirements and follows proper combustion safety procedures.

Cowboys AC specifically notes that their technicians are trained to ensure installs are safe and up to Texas code.

Mistake 4: Choosing the Wrong Type of Heating System for Your Home

Many homeowners assume they must replace “like for like,” but you often have options that may fit your home better—especially if you’ve had comfort issues in the past.

Cowboys AC installs multiple heating system types, including:

• Gas furnaces

• Electric furnaces

• Heat pumps

• Ductless mini-splits with heating

• Dual fuel systems

• Packaged heating units

For example:

• If you want high efficiency and year-round performance, a heat pump may be worth considering.

• If you have persistent hot/cold spots or an addition/garage that never feels right, ductless heating can provide targeted comfort without relying on old ductwork.

• If your home’s comfort varies by zone, you may benefit from a system design that better matches your layout.

The right choice depends on your comfort goals, budget, and the way your home is built—not just what you’ve used in the past.

Mistake 5: Skipping the “Total System” Check (Thermostat, Airflow, and Controls)

A furnace installation isn’t only “swap the box.” Thermostats, safety controls, airflow balance, and return sizing all impact performance. Cowboys AC even offers options like smart heating systems as part of their service mix.

If these details aren’t handled correctly, homeowners can end up with:

• Uneven heating across rooms

• Noisy operation

• High energy use

• Short cycling or frequent service calls

The Simple Solution: Hire Licensed, Experienced Pros from the Start

The easiest way to avoid installation mistakes is to work with professionals who handle the entire process correctly—from system selection and sizing to duct connections and safe venting.

Cowboys AC’s heating installation services emphasize licensed and NATE-certified expertise, code-compliant workmanship, and a wide range of heating options so you can choose what’s best for your home.

Not quite ready to replace your system? Cowboys AC also promotes heating tune-ups to help keep an older heater running safely and efficiently.

Need Furnace Installation Help in San Antonio or Selma?

If you’re planning a furnace installation or replacement in San Antonio, Selma, or the surrounding area, Cowboys Air Conditioning & Heating is ready to help you avoid costly mistakes and get a system that performs the way it should.

📞 Call Cowboys AC at (210) 495-7771 to schedule an in-home estimate and talk through the best heating installation option for your home.