Air Filtration Requirements for New Construction Homes in NC

What Carolina Builders Need to Know About MERV Ratings, Ventilation, and Certification

Happy pollen season! Spring has arrived in the Carolinas, and with it comes the annual yellow-green dusting of pollen on every car, porch, and windowsill. For millions of allergy sufferers, this time of year is a seasonal battle against sneezing, itchy eyes, and congestion. But here’s something many homeowners don’t realize: the front line of that battle isn’t outside — it’s inside your HVAC system. In this blog post, we’ll talk about the importance of thinking about air quality, and how to discuss it with homebuyers.

At Southern Energy Management, we spend our days helping homeowners and builders achieve HERS ratings, ENERGY STAR for Homes certification, and other high-performance building standards. And time and again, the humble air filter comes up as one of the most overlooked components in a healthy, efficient home. 

Why are air filters so important? Every time your HVAC system runs, it pulls air from inside your home through the filter before conditioning it. That means the air your home (and you) breathe is directly related to your air filtration strategy.

A clean, properly-rated filter captures pollen, dust mite debris, pet dander, and mold spores before they get recirculated through your living spaces.

A clogged or low-quality filter? It becomes a liability — restricting airflow, reducing HVAC system efficiency, and letting particles pass through that should have been caught.

Why Air Filtration Matters More for New Construction in the Carolinas

Pollen counts in the Southeast are among the highest in the nation during spring. Tree pollen (oak, pine, birch) peaks in March–April, grass pollen follows in May–June, and mold spores thrive wherever humidity climbs. And though the most showy pollen is that thick yellow pine pollen we all know so well, it’s actually the much smaller, much less visible grass pollen that’s responsible for most allergies! So for our builder partners, air quality is particularly important given our colorful environmental conditions and humid, moist composure.

Many people think they can insulate themselves from allergens and other pollutants by staying indoors, but this is exactly backwards. Studies by the EPA have actually shown that indoor air often contains as much as 2-5x as many pollutants in homes as can be found outside, especially in residences near industrial areas. And given that most people spend 21-22 hours a day indoors, that makes improving air quality all the more important. 

Why Green Building Programs Care About Your Air Filter

This might surprise some folks: air filtration is a real, scored component in programs like ENERGY STAR for Homes and SEM’s own ecoSelect. Energy efficiency, we now understand, goes hand in hand with air quality.

A Clean System is a Lean System

Without a good filter, particulates like dust, lint, and some mold spores can begin to build up critical components. A build up on your evaporator coil can slow heat transfer, making the air that comes out of your system the wrong temperature. A build up on the blower makes it work harder and begin to strain. Either way, it results in a system that runs longer and harder, yet to less effect meaning homebuyers pay high bills for less comfort. 

Building Tight vs Ventilating Right

You may well have heard the old adage that “homes need to breathe” as a rebuttal to increasing efficiency standards. And there is some truth to the saying. In the 1980s, when we were first deploying new energy efficient practices at scale, some homes were built in such a way that moisture was unable to escape the thermal boundary, leading to moisture and mold issues. 

Forty years later though, we have a much better grasp of how to build towards greater efficiency without compromising on air quality. First, we now understand that homes themselves do not need to breathe, per se—they need to dry out. Fortunately, we have come a long way with introducing draining planes and flashing into wall systems, as well as having exhaust fans in the areas of the home most likely to introduce new sources of moisture into the air, eliminating the most worrisome sources of those early moisture issues. 

That said, as we build homes tighter, we do need to contend with the thing inside homes that very much do need to breathe—people. Fortunately, we have made good progress on this front as well. We now know that the math checks out such that it makes economic sense to continue to build tighter while introducing fresh air ventilation systems into the construction process.  Even the energy used in mechanical ventilation is more than made up for by the decrease in energy used in sufficiently tight homes.

How much ventilation does a home need? 

The appropriate amount of ventilation for a home is determined by ASHRAE standard 62.2, which determines the cubic feet per minute (cfm) the fan must blow in relation to the floor area of the home and the number of bedrooms. The exact formula is Q_fan = 0.01A_floor + 7.5(N_br + 1), where Q_fan is flow in cfm, A_floor is floor area, and N_br is the number of bedrooms. 

For builders concerned about trying to meet this standard, our field raters are trained to program mechanical ventilation systems to meet this standard. Currently, ASHRAE 62.2 is not a requirement to meet code in NC or SC, but is required for ENERGY STAR, NGBS, and DOE ZERH, and as such compliance with this standard is a way for builders to differentiate themselves from the competition. 

MERV Ratings for New Construction Homes 

Not all filters are created equal. The industry uses a scale called MERV (Minimum Efficiency Reporting Value) to rate how effectively a filter captures airborne particles. The scale runs from 1 to 20 with 1 being on the low end of filtration.

For most new construction homes, a MERV 6-9 filter hits the sweet spot: effective enough to meaningfully reduce allergen load without over-restricting airflow. Going too high without a compatible HVAC system can actually strain your equipment. In general, you should be fine with anything that is MERV 9 or lower, though the brand and model may make a difference. That said, if you live in a household with someone who has severe allergies or is immunocompromised, it may be worth it to retrofit your HVAC system to accommodate something more potent. If so, consult with your doctor and an HVAC professional.

Air Filtration Requirements by Certification Program

ecoSelect

MERV 6 (Requirement 2.3)

ENERGY STAR

MERV 6 (Requirement 9.1)

Indoor Air Plus

MERV 8 for Indoor Air Plus Certified (Section 4.6.6.1)
MERV 13 for Indoor Air Plus Gold

DOE Efficient New Homes

(Formerly DOE Zero Energy Ready Homes)
Need to pass Indoor Air Plus

National Green Building Standard (NGBS)

MERV 8 (Section 1205.11)

What does a HERS rater verify related to air filters?

When it comes to inspection time, your HERS rater will check that the air filters installed on site are up to spec for meeting any program requirements you are trying to achieve.

When and Where to Buy Air Filters

Air filters in new construction homes must be changed before a home closes, as per Section 605.1 of the North Carolina Mechanical Code. You’ll want to change these as late as you can in the construction process so they don’t accumulate a bunch of drywall, paint, and saw dust, but definitely before your rater arrives to inspect the home.  

You can pick up air filters at any hardware store. The MERV Rating should be printed on the package, though if there is not one, you can assume it is somewhere between MERV 1-4. Code only requires that air filters of any MERV rating be present prior to closing, so these simple fiberglass ones will get you your CO, but they will do little for the home’s air quality, and may be considered an eye sore by home buyers. MERV 5-13 filters have pleasant white pleating with white cardboard casing, and will not only not draw attention to themselves but will do much more for the eventual homeowner. 

Reach out if you’re curious about your air quality strategy. We’re happy to review your plans and make sure you’re on the path to providing good air quality.