Usually, Yes

Most central air-handling units can be retrofitted. A plate core often slots into the AHU section with minimal ductwork changes; a rotary wheel needs space for the wheel and its drive.

What to Check First

• Physical space in or beside the AHU
• Balanced supply and exhaust airflow
• Available fan capacity for the extra pressure drop
• Controls to manage frost protection if needed

Retrofit Tips

Start with a crossflow plate core for simplicity. Verify the fan can handle the added static pressure before committing, and model the savings at your actual operating hours.

Payback

Retrofits in continuously ventilated buildings often pay back within a few seasons because the duty runs year round.

Plate and Heat-Pipe Units

These are nearly maintenance free. Inspect annually, vacuum or wash the core if it collects dust, and check for leakage between airstreams if performance drops.

Rotary Wheels

The wheel adds a motor, seals, and bearings. Plan for periodic media cleaning, seal inspection, and drive-belt or bearing checks per the manufacturer schedule.

Filters Matter

Good upstream filtration keeps the core clean and extends intervals. Dirty filters also raise pressure drop and fan energy, so replace them on schedule.

What to Track

• Pressure drop trend (rising drop signals fouling)
• Supply-air temperature (falling effectiveness signals blockage or leakage)
• Motor current on rotary units

The Trade-off

Neither is universally better; they solve different problems.

Choose Plate When

• You want no moving parts and minimal maintenance
• Air streams must stay fully separated (hospitals, labs)
• Moisture recovery is not required

Choose Rotary When

• You need the highest effectiveness (up to 85 percent)
• You must recover humidity in a humid climate
• The unit is large enough to justify the motor and seals

Simple Rule

If isolation and simplicity matter most, pick plate. If peak performance and moisture recovery matter most, pick rotary. See our full comparison for the detailed table.

Why It Happens

When cold outside air meets warm, moist exhaust air inside the core, the exhaust can drop below 0 C and ice forms. Left alone, ice blocks the channels and destroys effectiveness.

Common Solutions

• Defrost bypass - periodically send warm supply air through the exhaust side to melt ice.
• Preheat - warm the incoming air slightly before the core so exhaust stays above freezing.
• Recirculation - mix a little return air into the intake during extreme cold.
• Frost-resistant core - wider channels and hydrophobic surfaces slow buildup.

Which to Pick

For most commercial systems a timed bypass or a small preheat coil is enough. The right choice depends on how cold your winter design temperature is.

When Sensible Is Enough

In dry or cold climates, moisture is not the main load, so a sensible-only plate core is the cost-effective choice. It recovers temperature and ignores humidity.

When Enthalpy Pays Off

In hot, humid climates a large part of the cooling load is dehumidification. A sensible exchanger leaves that moisture in the incoming air, so the cooling coil still works hard. An enthalpy wheel or membrane plate pre-conditions both temperature and humidity.

How to Decide

• Hot and humid summer -> choose enthalpy recovery
• Cold and dry winter -> sensible plate is fine
• Mixed or variable climate -> membrane plate offers a middle path

Cost Note

Enthalpy devices cost more and need more care, but in the right climate they often halve the dehumidification load and shorten payback.

The Range

In most buildings, heat recovery cuts the ventilation-related heating and cooling load by roughly 50 to 80 percent. Cold climates with high heating demand see the biggest absolute savings; mild climates see smaller but still worthwhile gains.

What Drives the Number

• Local climate and design temperatures
• Exchanger effectiveness (higher is better)
• How balanced the supply and exhaust airflows are
• Run time - savings compound over 8,760 hours a year

A Quick Example

A 10,000 m3/h stream at a 20 K difference with 70 percent effectiveness recovers about 46 kW of heating load. Over a heating season that is a large, billable reduction in gas or electricity use.

Bottom Line

Recovery rarely pays for itself on first cost alone; it pays back through operating savings, usually within a few seasons in heated buildings.

Short Answer

Heat recovery efficiency, more precisely called effectiveness, is the percentage of the maximum possible heat that the exchanger transfers from the outgoing airstream to the incoming airstream.

Why a Percentage

A exchanger can never reach 100 percent, because the supply air would have to leave at the exact temperature of the exhaust air, which breaks the thermodynamic gradient. Real devices land between 50 and 85 percent depending on type and size.

Two Numbers to Know

• Sensible effectiveness - dry-bulb temperature recovery only.
• Latent (enthalpy) effectiveness - temperature plus moisture recovery.

What It Means for You

A 70 percent effective unit removes 70 percent of the heating (or cooling) load that ventilation would otherwise impose. That is the single number that drives your energy saving and payback.