HVAC systems are more efficient than they used to be, but these common HVAC mistakes can quickly erase any advantages of a new system.
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As one of the most expensive and energy-hungry aspects of your home, the heating, ventilation and air conditioning (HVAC) system requires careful installation, maintenance and control to provide the best service. Common HVAC mistakes that cause inefficiencies can happen during installation or because of improper maintenance and incorrect operation.
Some of these mistakes may need professional repair, but many don’t. They just call for a more thorough understanding of how your HVAC system works so that it can get the TLC it needs. Here, our experts explain the most common HVAC mistakes and what to do about them.
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Improperly Sizing Your Air Conditioner
According to Eric Weiss of Trane Residential, installing an air conditioner that’s too large or too small for the space is one of the most important HVAC mistakes to avoid.
If the AC unit is too small for the home, it runs longer, works harder and consumes more energy, and even then, it may never fully catch up to demand. All this shortens its life span. When oversized, the unit cycles on and off in short bursts, never really controlling humidity or cycling the air in the home. The constant on/off cycling also stresses the HVAC system and ages it prematurely.
Avoid this problem by having an HVAC tech help you determine the size of the unit you need before you buy one.
Replacing A Furnace With a Unit of the Same Size
Today’s blowers with variable-speed motors and sophisticated controllers move a lot more air than older units. Automatically replacing a furnace with a new model of the same capacity is one of those HVAC mistakes that can result in wasted energy and excessive noise.
“You shouldn’t assume the old size is the right size today,” advises Chicago HVAC tech Jon Gilbertsen. “If you improved insulation and installed new windows, you probably need something smaller, but if no upgrades have been made, you might actually need something a bit larger, since older homes tend to lose more heat over time without improvements.” This is another problem you can avoid by consulting an HVAC pro before you buy a new unit.
Installing an Overly Restrictive Air Filter
The MERV (Minimum Efficiency Reporting Value) rating of a filter measures its ability to remove particulate matter. The higher the MERV rating, the smaller the diameter of the particles it can trap and the cleaner the air it produces. Filters with high MERV ratings restrict air flow, which is another HVAC mistake that can be bad for the system.
“People often think a higher MERV rating is better,” says HVAC pro Josh Mitchell, “but if your blower wasn’t designed to handle it, airflow drops, and you can burn out motors. I recommend MERV 8 to 11 for most homes unless they’ve got asthma, allergies, or a newer variable-speed unit that can handle a higher load.”
Closing Too Many Vents to “Save Energy”
It’s a pretty common misconception that if you’re only using a portion of the house, closing the vents in the unused portion will save you money because the furnace or heat pump doesn’t have to work as hard. This HVAC mistake doesn’t save money and can actually ruin the system, according to Gilbertsen. “It creates pressure imbalances that strain the blower and cause duct leaks. It’s better to keep vents open and adjust the damper in the duct if you need less heating or cooling to a room.”
Putting Obstructions Too Close to Outdoor Coils
In an air-conditioning system, the condenser coil, which is outside the home, needs to stay at or near the ambient air temperature. If you try to disguise the condenser unit with landscaping, you can inhibit air flow around the condenser. In that situation, Weiss says that the air moving through the unit can run as much as 20 degrees hotter than the ambient air. This costs you as much as 15 percent of its capacity to cool your home and results in a power consumption increase of up to 20 percent — a costly double-whammy!
Gilbertsen also recommends being careful when mowing around the unit. “Debris and grass clippings that get sucked into the coils after mowing block airflow and force the system to run hotter, slowly killing it. Take a minute after mowing to check and gently rinse it off — it’s a five-minute job that saves you from a big repair bill later.”
Using Refrigerant Additives
“The oils and additives in the compressor vary from one model to another in order to maximize performance,” says Weiss. “Starting to throw in different additives can be very risky from a reliability perspective.”
Third-party maintenance technicians often try to sell these additives to homeowners as an add-on that boosts their margin. “We have tested many of these in the past and found negative results,” says Weiss. “Others we tested and haven’t seen much change. We really don’t want any of that in the system.”
This is one of the easiest HVAC mistakes to avoid. Just skip the additives.
Cleaning the Coils with Corrosive Chemicals
It’s a very good idea to periodically clean the condenser and evaporative coils on your central AC unit or heat pump to maintain efficiency, but don’t use the wrong cleaners, says Gilbertsen. “You should avoid harsh, acidic cleaners, but there are coil cleaners made specifically for HVAC that are safe and effective when used correctly. Low-pressure water works for light dirt, but stubborn buildup sometimes needs the right cleaner.” Simple Green and CRC foaming coil cleaners are two safe, effective products that cost less than $10.
Running the Blower Continuously in Humid Climates
In hot, dry climates, such as in Phoenix, AZ, Weiss recommends running the HVAC blower continuously to even out the distribution of cool air throughout the home. In the more humid environs of Texas and the Midwest, however, he recommends installing a variable-speed blower or setting it to come on only when the compressor runs. Why? Using the blower continuously raises the relative humidity level within the home by six to 10 percent, which will make you feel even less comfortable.
If you can’t upgrade to a variable-speed blower right now, Gilbertsen recommends setting the fan to ‘auto’ so it only runs when the AC is actively cooling.
Failing to Include a Return in a Room With a Door
An air return helps air cycle through the system by routing it from the room back to the furnace-A/C blower to be reconditioned. Although opening a vent in a room without a return technically can meet code, Weiss says that any vent needs a clear path for the air to reach a return.
Here’s why this is important: If the door to a room containing a vent with no return gets closed, the pressure in that room goes positive, forcing the rest of the home into a negative-pressure state. Negative pressure pulls air into the home from any possible opening, bypassing the HVAC system and possibly trapping exhaust from gas appliances inside your home.
While a return in a room with a door is super important, it’s not the only way to handle the situation, adds Gilbertsen. If you don’t have a return in a room with a door, you need a transfer grille, jump duct, or at least ¾ inch of clearance between the bottom of the door and the finished floor to let air flow freely.
Placing Thermostats Near Heat Sources
The reason your house is habitually cold, even though the HVAC system seems to be working fine, could be the placement of the thermostat. “I’ve walked into homes where the thermostat is right above a lamp or across from a sunny window,” says Mitchell. “That skews readings and messes with the cycle timing.”
Moving a thermostat is not a big job, but it involves running new wires and reconnecting them. If that’s beyond your abilities, hiring as pro to do it will probably cost from $200 to $400. The best place for a thermostat is on an inside wall, away from direct sunlight or appliances — and not in the kitchen.
Forgetting to Seal Duct Connections
Any air that escapes through leaky ducts is air that isn’t conditioning your home, and that’s a massive energy waste, according to Mitchell. “A leaky system can lose up to 30% of conditioned air, especially in attics and crawl spaces.”
Ducts leak most often around the seams, and you can seal the leaks with tape, but Mitchell cautions not to use duct tape, even though that’s ostensibly what this type of tape is for. Instead, he recommends foil tape, which costs about $30 per roll, or mastic, which you can buy by the packet for small jobs (about $5) or by the bucket for large jobs (from $20 to $40).
Failing to Measure Static Pressure
Static pressure is the resistance to airflow in the ducts, and if it’s too high, the blower has to work harder to circulate air into the building. HVAC techs measure this pressure using a manometer, and Mitchell advises that you should do it during every service call.
“High static pressure puts strain on the blower and can cut airflow by 20% or more. I always carry a manometer and check it on tune-ups.”
FAQ
If my HVAC guy makes a mistake, do I have to pay for it?
If a mistake happens, a reputable company will take responsibility for it, and you shouldn’t have to pay. Where it gets tricky, says Gilbertsen, is if the “mistake” turns out to be a misdiagnosis because the problem wasn’t obvious at the time of service. “In that case, you might still be on the hook for the extra work. The best protection is hiring someone reputable and getting everything in writing, so there’s no arguing later.”
About the Experts
- Eric Weiss is the Technical Training Manager at Trane Residential.
- John Gilbertsen is the President and CEO of Chris Heating & Cooling, based in West Chicago, Il.
- Josh Mitchell is an HVAC technician and the owner of Air Conditioner Lab, an online resource for air conditioners, heaters and air purifiers.
