If you are deciding between an ERV and an HRV for a residential or light commercial job, the core installation difference comes down to how each unit handles moisture: an HRV (heat recovery ventilator) exchanges heat only and is built for cold, dry climates, while an ERV (energy recovery ventilator) also transfers humidity and suits hot, humid or mixed climates. That single distinction drives every downstream choice—ductwork configuration, condensate management, defrost strategy, and which code sections apply. For a pro, the practical rule is: match the core to the climate, then match the duct layout to the house, not the other way around.
An HRV transfers sensible heat—temperature—between the outgoing stale air and the incoming fresh air. In winter, the outgoing warm air warms the incoming cold air; in summer, the reverse happens if the system runs in cooling mode. It does not transfer water vapor. An ERV transfers both sensible heat and latent heat—moisture. Its enthalpy core moves humidity along with temperature, so in summer it pulls moisture out of incoming humid air, and in winter it retains some indoor humidity that would otherwise be exhausted.
The mechanical result: an HRV in a cold climate prevents the indoor air from becoming overly dry, because it dumps humid indoor air outside. An ERV in that same climate would keep more moisture inside, which can push a tight home toward condensation issues. Conversely, in a humid climate, an HRV would drag humid outdoor air inside with little to no moisture removal, while an ERV actively reduces the humidity load on the air conditioner.
For the installer, this is not a marketing nuance. It changes the size of the unit, the ductwork layout, and whether you need to run a condensate drain line. An HRV core in a cold climate will frost up and need defrost cycles; an ERV core is less prone to frosting but still needs attention in extreme cold. You are not just swapping a part—you are committing to a different system behavior for the life of the house.
The ductwork differences are real but often overstated. Both units use the same basic four-port configuration: fresh air intake from outside, exhaust air to outside, supply air to the living space, and return air from the living space. The differences show up in three areas: balancing, condensate, and defrost bypass.
Balancing is more critical on an HRV. Because an HRV only exchanges heat, an imbalance in airflow—say, 10% more supply than exhaust—creates a slight pressure imbalance that can pull in untreated outdoor air through cracks. An ERV, with its enthalpy core, is more forgiving of minor imbalance because the moisture transfer partially compensates. In practice, you should still balance both to within 10%, but the tolerance for sloppy work is narrower on an HRV. Use a flow hood or a calibrated pitot tube and static pressure probe on every job, not just when the inspector asks.
Condensate drain is mandatory on an HRV in cold climates. When the core frosts and defrosts, the meltwater has to go somewhere. Most HRVs include a drain pan and a condensate port. You must run a drain line to a floor drain, a condensate pump, or an exterior termination with a P-trap. An ERV in a humid climate also produces condensate during summer cooling, so do not assume an ERV skips the drain—check the manufacturer's installation manual for the specific model. As a rule of thumb, if the unit has a drain port, use it. If it does not, verify that the core is designed to handle moisture without drainage.
Defrost bypass ducting is a common differentiator. Many HRVs have an internal electric preheater or a recirculation defrost mode, but some budget units require an external bypass damper to route air around the core during defrost. That is an extra duct run, an extra damper, and an extra control wire. ERVs typically handle defrost differently—often by simply reducing supply airflow—so they rarely need the external bypass. If you are quoting a job and the spec sheet mentions an "external defrost bypass," budget for an additional 2–3 hours of ductwork and controls labor.
Duct material and insulation also differ by climate, not by unit type. In a cold attic, both supply and exhaust ducts need R-8 or better insulation to prevent condensation on the exterior of the duct. In a humid crawlspace, you need a vapor barrier on the duct exterior. The unit type does not change this—the climate does. Do not let a supplier talk you into skipping insulation because "it's an ERV, so it handles moisture." The core handles moisture; the duct does not.
The climate decision is the single most important factor in choosing between the two, and it is also where most installers get it wrong by relying on vague rules like "ERVs are for the South, HRVs are for the North." That is directionally correct but misses the nuance of mixed climates and heating-dominated versus cooling-dominated regions.
HRVs are the default for heating-dominated climates—roughly, regions with more than 4,000 heating degree days (HDD) per year. That covers most of the northern US, the upper Midwest, and the Northeast. In these climates, winter indoor humidity is typically 20–35% relative humidity (RH), and an HRV preserves that dryness, which is actually desirable because it prevents window condensation and mold on cold surfaces. An ERV in the same climate would hold humidity inside, and in a tight house with a humidifier, that can push RH above 50%, leading to condensation in wall cavities.
ERVs are the default for cooling-dominated and humid climates—roughly, regions with more than 2,000 cooling degree hours and high summer dew points, like the Southeast, Gulf Coast, and mid-Atlantic. In these regions, summer outdoor dew points regularly exceed 70°F, and an HRV would bring that humidity straight into the house. An ERV's enthalpy core reduces the latent load by 50–70%, which means the air conditioner does less work and the indoor RH stays below 55% without over-cooling.
The tricky zone is mixed climates—the Pacific Northwest, parts of the Midwest, and the mid-Atlantic transition zone. Here, the answer depends on the dominant problem. In Seattle, winter heating dominates, but summer humidity is rarely oppressive; an HRV is usually the right call. In St. Louis, you have both cold winters and humid summers; an ERV is often better because the summer dehumidification benefit outweighs the winter moisture retention. As a rule of thumb, if the house has central air conditioning and the summer dew point regularly exceeds 65°F, choose an ERV. If the house relies on heating for more than 7 months of the year and summer humidity is a non-issue, choose an HRV.
One more climate factor: the defrost penalty. In very cold regions—below -10°F outdoor temperature—both units will spend significant time in defrost, during which they are not ventilating. An HRV with an electric preheater will still ventilate during defrost but at reduced efficiency. An ERV in extreme cold may need a preheater to prevent core frosting. If you are installing in northern Minnesota or northern Maine, check the unit's minimum operating temperature spec and consider a preheater regardless of unit type.
Code requirements vary by jurisdiction, but there are national baselines that apply to most residential work. The two big ones are the International Residential Code (IRC) and the International Mechanical Code (IMC), plus ASHRAE 62.2 for ventilation rates. Most states adopt these with local amendments, so always check the local code before bidding.
ASHRAE 62.2 ventilation rate is the starting point. The formula for a dwelling unit is: 7.5 CFM per occupant plus 1 CFM per 100 square feet of conditioned floor area. For a 2,000-square-foot home with three occupants, that is 7.5 × 3 + 2,000 / 100 = 22.5 + 20 = 42.5 CFM continuous. Most ERV and HRV units are sized at 80–120 CFM at their highest speed, so you will typically run them at low or medium speed continuously. The code does not require a specific unit type—it requires a minimum ventilation rate. The unit type is your choice, but the rate is not.
Duct leakage testing is increasingly required. Many jurisdictions now require duct leakage testing for new construction, and ventilation ducts are included. The IRC requires total duct leakage to be less than 4 CFM per 100 square feet of conditioned floor area for new construction, and less than 8 CFM per 100 square feet for existing homes. That means you need to seal every joint with mastic, not just foil tape. Use mastic on all accessible joints and a pressure-sensitive aluminum tape on the rest. Do not rely on duct sealant spray—it is not a substitute for proper joint preparation.
Termination requirements are specific and often violated. The fresh air intake must be at least 10 feet from any appliance vent, chimney, or plumbing vent, and at least 3 feet from any dryer vent or exhaust fan termination. The intake must also be at least 12 inches above grade, and in snow-prone regions, at least 24 inches above the expected snow line. The exhaust termination must be at least 3 feet from any window or door that can open, and at least 10 feet from the intake. Many inspectors will flag a termination that is too close to a gas meter or an air conditioner condenser. Check the local code for setback distances—they vary.
Electrical requirements are straightforward but easy to miss. Most residential ERVs and HRVs run on 120V and draw 1–3 amps, but they need a dedicated circuit in many jurisdictions. The unit must be on a GFCI-protected circuit if it is within 6 feet of a sink or in a garage or basement. You also need a disconnect within sight of the unit. The control wiring—typically 24V thermostat wire—must be rated for the application and run in a separate conduit from line voltage if the run exceeds 6 feet.
The biggest code pitfall is the condensate drain. The IRC requires condensate drains to be trapped and to discharge to an approved location—a floor drain, a laundry sink, or the exterior. You cannot discharge condensate into a vent stack or a sanitary sewer without a trap and an air gap. Many jurisdictions also require a secondary drain pan with a float switch for units installed above finished ceilings. If you are installing an HRV in an attic, budget for the secondary pan and the float switch—it is code in most places and a cheap insurance policy.
The equipment cost difference between an ERV and an HRV is smaller than most homeowners expect, and the installation cost difference is often negligible. What moves the needle is the complexity of the ductwork, not the unit type.
Equipment cost. As an illustration, budget $800–$1,500 for a residential HRV and $900–$1,800 for a comparable ERV from the same manufacturer. The ERV premium is typically 10–20% because the enthalpy core is more expensive to manufacture. That is a $100–$300 difference at the equipment level—not a deal-breaker, but worth quoting honestly. Do not upsell an ERV to a homeowner in a dry climate just to increase the ticket; it is not a better product for that application.
Installation labor. The labor is nearly identical for both units if the ductwork is the same. You are looking at 8–16 hours for a typical retrofit installation, depending on accessibility. At $75–$150 per hour, that is $600–$2,400 in labor. The variance comes from the ductwork, not the unit. A simple open-basement install with short runs to an exterior wall is at the low end; a two-story house with runs through conditioned attic space is at the high end.
The cost driver is ductwork, not the unit. For a retrofit, you are often adding 4–6 new duct runs: a supply to the main living area, a return from the bedrooms, and exterior terminations. Each run of 6-inch insulated flex duct costs $2–$4 per linear foot, plus fittings, hangers, and termination hoods. A typical retrofit runs $500–$1,500 in duct materials alone. If you are installing in new construction, the cost drops because the duct is part of the rough-in.
A worked example, illustrative only. Assume a 2,000-square-foot ranch house in the Midwest with an unfinished basement. You need 42.5 CFM continuous, so you choose a mid-tier HRV rated at 120 CFM. Equipment: $1,100. Ductwork: 60 linear feet of insulated flex at $3 per foot, plus 4 termination hoods at $40 each, plus fittings and hangers at $150—total $490. Labor: 12 hours at $100 per hour—$1,200. Total: $2,790, plus permit fees and any electrical work. If you swap in an ERV at $1,300, the total becomes $2,990. The difference is $200—about 7% of the job. The homeowner's decision should be based on climate, not cost.
The hidden cost is the control system. Many ERVs and HRVs come with a basic wall controller, but homeowners often want a smart controller with humidity sensing, scheduling, and integration with a smart thermostat. That adds $150–$400 to the job and 1–2 hours of setup. If the unit is tied into a zoned HVAC system, you may need a relay panel and additional wiring—another $200–$500. Quote the control system separately so the homeowner sees the full picture.
The mistakes that cost you callbacks are rarely about the unit itself—they are about the installation details that show up six months later when the homeowner notices condensation, noise, or high energy bills.
Mistake 1: Undersizing the duct runs. A 120 CFM unit needs a 6-inch duct for the main supply and return runs, and 5-inch for branch runs. If you use 4-inch flex to save money, you will see a static pressure increase that reduces airflow by 20–30% and increases noise. Always check the manufacturer's minimum duct size chart. If the unit has a 6-inch collar, do not neck it down to 4-inch.
Mistake 2: Forgetting the balancing dampers. Every ERV and HRV needs balancing dampers in the supply and exhaust runs to fine-tune airflow after installation. If you skip them, you cannot balance the system, and the unit will either over-ventilate or under-ventilate. Install a balancing damper in each run, and label them so the homeowner knows what they are for.
Mistake 3: Poor intake placement. The fresh air intake must be away from the dryer vent, the kitchen exhaust, the bathroom exhaust, and any combustion appliance vent. If the intake is downwind of the dryer vent, you will pull lint and moisture into the unit. If it is near the gas water heater vent, you will pull carbon monoxide into the house. This is a safety issue, not just a performance issue. Walk the exterior of the house before you cut any holes.
Mistake 4: Skipping the condensate trap. An untrapped condensate line will allow sewer gas or outside air to flow back into the unit. The trap must be at least 2 inches deep and primed with water before startup. If you skip the trap, you will get a call about a musty smell within a month.
Mistake 5: Ignoring the filter access. Both units have filters that need replacement every 3–6 months. If you install the unit in a location where the filter is inaccessible—behind a water heater, in a tight attic corner—the homeowner will never change it, and the unit will lose efficiency and eventually fail. Install the unit with at least 24 inches of clearance on the filter side.
Mistake 6: Not testing airflow after installation. The manufacturer's spec sheet says the unit moves 120 CFM, but that is at zero static pressure. In a real installation with 50 feet of duct and two elbows, you will see 80–90 CFM. Use a flow hood or a pitot tube to measure actual airflow at the supply and exhaust terminations. If the airflow is below the ASHRAE 62.2 requirement, you need to either increase fan speed or reduce duct resistance. Do not sign off on the job until you have verified the numbers.
Mistake 7: Confusing the supply and exhaust ports. It sounds basic, but it happens. The fresh air supply port must connect to the duct that feeds the living space. The exhaust port must connect to the duct that pulls from the bathrooms and kitchen. If you reverse them, you will pressurize the house with stale air and depressurize the bathrooms. Label the ports during installation and verify the airflow direction before you seal the duct.
The decision tree is straightforward once you separate climate from the house specifics. Start with the climate zone, then adjust for the house's existing humidity profile.
Step 1: Determine the dominant season. If the house is in a heating-dominated climate (more than 4,000 HDD), lean HRV. If it is cooling-dominated or humid (summer dew points above 65°F), lean ERV. If it is mixed, move to step 2.
Step 2: Check the house's humidity behavior. If the homeowner complains about dry air in winter—static shocks, cracked wood, nosebleeds—an HRV will make it worse. An ERV will retain more moisture. If the homeowner complains about sticky summers and the AC runs constantly, an ERV will reduce the latent load. If the house has a humidifier already, an HRV is the safer choice to avoid over-humidification.
Step 3: Consider the ductwork reality. If the house has an existing duct system you can tap into, either unit works. If you are adding a dedicated ventilation duct system, the cost difference is negligible, so choose based on climate, not cost. If the house is a tight new construction with a blower door test result below 3 ACH50, you need a balanced ventilation system—either unit qualifies, but you must balance it carefully.
Step 4: Check the local code and utility incentives. Some jurisdictions require ERVs for new construction in humid climates, and some utilities offer rebates for energy recovery ventilators specifically. Check the local code and the utility's current program page before you quote. Do not assume the rebate amount—it changes frequently.
Step 5: Make the call and explain it. The homeowner will ask which is better. The honest answer is: it depends on the climate and the house. Give them the reasoning, not just the recommendation. If you can show them the ASHRAE 62.2 calculation and the climate data, they will trust the decision.
Yes, but you need to manage the defrost cycle. An ERV in a cold climate will retain indoor humidity, which can cause condensation issues in a tight house. If the house has a humidifier or high internal moisture loads, an HRV is safer. If you do install an ERV in a cold climate, verify the unit's minimum operating temperature and consider a preheater for extreme cold.
Technically yes, but it is a poor choice. An HRV does not transfer moisture, so in a humid climate it will bring humid outdoor air inside without reducing the humidity. The air conditioner will have to work harder, and the indoor RH will stay high. An ERV is the better choice for any climate with summer dew points above 65°F.
Most HRVs in cold climates require a condensate drain for defrost meltwater. Many ERVs in humid climates also produce condensate during summer cooling. Check the manufacturer's installation manual for the specific model. If the unit has a drain port, use it. If it does not, verify that the core is designed to handle moisture without drainage.
Use the ASHRAE 62.2 formula: 7.5 CFM per occupant plus 1 CFM per 100 square feet of conditioned floor area. For a 2,000-square-foot home with three occupants, that is 42.5 CFM continuous. Most residential units are rated at 80–120 CFM, so you will run them at low or medium speed. Oversizing is common and wasteful—match the unit to the calculated rate, not the square footage alone.
As an illustration, budget $2,500–$4,500 for a complete retrofit installation, including equipment, ductwork, labor, and controls. The equipment difference between an ERV and an HRV is typically $100–$300, which is a small fraction of the total. The cost driver is the ductwork and labor, not the unit type. Price it against your own supplier and labor rates.
Most jurisdictions require a mechanical permit for any ventilation system installation, including ERVs and HRVs. The permit fee is typically $50–$200, and the inspection ensures that the terminations, duct sealing, and condensate drain meet code. Skipping the permit can create liability if there is a fire or carbon monoxide issue later. Pull the permit—it is cheap insurance.
Before you quote another ventilation job, pull the ASHRAE 62.2 calculation for the specific house and write the required CFM on the proposal. Then verify the local code's termination setback distances and condensate drain requirements. That single sheet of paper will separate you from every contractor who is just swapping boxes based on a vague climate rule.
This article was produced with AI assistance. Figures are illustrative estimates — verify current prices, programme amounts, and code requirements locally before acting on them.