What Is a Window ERV?
What Is a Window ERV?
A window ERV (energy recovery ventilator) is a ventilation machine that installs in an open sliding or double-hung window. It continuously pushes stale indoor air out and pulls fresh, filtered outdoor air in, while an energy recovery core transfers heat and moisture between the two air streams so you keep most of the energy you paid to heat or cool your home.
It solves the problem air purifiers cannot. Purifiers recirculate the same air and catch particles. They do nothing about CO2, VOCs, radon, cooking fumes, or odors, because gases pass straight through filters. The only fix for gases is air exchange. A window ERV does that exchange without the cost and discomfort of an open window.
How it works
The core of a window ERV is a heat exchanger. In SWERV's case it is a desiccant-coated ceramic core with reversible fans. The fans exhaust room air through the core, which captures its heat and moisture, then reverse and pull outdoor air back in through the same core, which returns that heat and moisture to the incoming stream. The cycle repeats every 45 seconds. In winter the incoming air arrives pre-warmed. In summer, pre-cooled. Incoming air passes through a MERV 13 filter with activated carbon, so pollen, smoke, and dust stay outside.
The result: fresh air, roughly 85% of your energy retained, and none of the noise, pollen, humidity, or security tradeoffs of an open window.
Window ERV vs the alternatives
| Option | Removes CO2/gases? | Energy | Install | Cost |
|---|---|---|---|---|
| Open window | Yes | Wastes 100% of conditioned air | Free | Free, but often $100s-$1,000+/yr in wasted energy |
| Window fan | Yes | Wastes 100% | Minutes | $30-$100 plus energy waste |
| Air purifier | No | Neutral | None | $100-$800 |
| Through-wall ERV | Yes | Recovers 60-80% | Drilled 7" holes, usually pro install | $2,500-$20,000 installed |
| Whole-home ducted ERV | Yes | Recovers 50-85% | Ductwork, contractor, days | $6,000-$40,000 installed |
| Window ERV | Yes | Recovers ~85% | 10 to 15 minutes, no contractor | Under $1,000 |
Who a window ERV is for
- People measuring high bedroom CO2 (1,000-2,500+ ppm overnight is normal in sealed bedrooms) who wake up groggy or with headaches
- Renters and condo owners who cannot modify walls
- Tight, spray-foamed, or hurricane-windowed homes with no mechanical ventilation
- Rooms where opening the window fails: too cold, too humid, street noise, pollen, wildfire smoke, ground-floor security
- Kitchens with gas stoves and no vented range hood
- Rooms fighting humidity and mold pressure
Who it is NOT for
A window ERV needs a double-hung, single-hung, or horizontal sliding window with a clear opening of at least 23 inches that opens at least 6 inches. Over 48 inches works too, email us for free extra foam blocks. If you only have casement, awning, or tilt-and-turn windows, a through-wall ERV is the better fit. If your only problem is particles (dust, pollen, dander) with no CO2 or odor issue, an air purifier is cheaper.
What it costs to run
SWERV draws about 10 watts in typical use and 42 watts at most, about the cost of an LED bulb. Compare that to the hidden cost of a cracked window: exhausting conditioned air at ventilation rates can waste hundreds to over a thousand dollars a year in heating and cooling depending on climate. That is why a window ERV typically pays for itself in 1-2 years for people who currently open windows for fresh air.
The measurable result
Customers with CO2 monitors (Aranet4, Airthings, AirGradient) typically see 40 to 70% lower CO2 in the room the unit serves. One Florida customer went from 1,000+ ppm to a steady 400-600 ppm with a single unit at 26-40% speed.
SWERV is the first modern, mass-market window ERV. It installs in 10 to 15 minutes with no contractor. See specs and pricing at the product page, or start with why bedroom CO2 climbs overnight.