Atmospheric gas water heaters use natural draft through a B-vent chimney to vent combustion gases. Power vent models use a fan-assisted blower to push combustion gases through PVC sidewall venting. The choice is dictated primarily by your home\'s existing venting infrastructure.
Side-by-side
| Atmospheric | Power Vent | |
|---|---|---|
| Venting | Vertical B-vent chimney | 2"/3" PVC sidewall or roof |
| Electrical | Not required (no fan) | 120V outlet for blower |
| Combustion air | Room air (50 cu ft/1000 BTU) | Room air (some sealed-combustion variants exist) |
| Equipment cost | Lower ($649-849 for 50-gal) | $200-400 higher than atmospheric |
| Install complexity | Simpler (with existing chimney) | More complex (PVC routing) |
| Backdraft risk | Possible (tight homes, kitchen exhaust) | Minimal (positive pressure exhaust) |
| Vent termination | Roof penetration | Sidewall penetration (12" above grade) |
When atmospheric fits
- Existing B-vent chimney in good condition
- Adequate room air supply (50 cu ft per 1000 BTU)
- No power-vent retrofit complications
- Budget priority (atmospheric is the cheaper hardware)
- Like-for-like atmospheric replacement
When power vent is required
- No existing chimney (1990s+ construction often skipped chimneys)
- Existing chimney condemned, deteriorated, or too small
- Tight home with depressurization concerns (kitchen exhaust, dryer, fireplace creating backdraft on atmospheric)
- Want to relocate water heater away from chimney path
- Reclaiming chimney space for interior remodel
Power vent install requirements
- 120V dedicated outlet within 6 ft for blower
- 2" or 3" PVC venting Schedule 40 — sized per manual
- Equivalent length typically max 40-60 ft (varies by model)
- Sidewall termination: 12" above grade; 12" from windows/inlets
- Slope: ¼" per foot back toward unit for condensate drainage
- Condensate trap at low point
Backdraft — the atmospheric concern
Modern airtight homes can create depressurization that pulls flue gases back into living space from atmospheric water heaters. Common triggers:
- Kitchen range hood at high speed
- Whole-house exhaust fan
- Dryer running
- Fireplace exhaust
- HRV/ERV imbalance
If your home experiences backdraft on atmospheric water heaters, options:
- Switch to power vent (positive exhaust pressure overcomes backdraft)
- Add dedicated combustion air supply ducted from outdoors
- Switch to sealed-combustion gas tankless or condensing
- Switch to electric water heater (eliminates combustion entirely)
Cost comparison (50-gallon class installed)
| Type | Equipment | Install labor | Total |
|---|---|---|---|
| Atmospheric like-for-like | $649-849 | $400-600 | $1,050-1,450 |
| Power Vent new install (no existing PVC) | $1,049-1,399 | $700-1,200 | $1,750-2,600 |
| Power Vent like-for-like replacement | $1,049-1,399 | $500-800 | $1,550-2,200 |
Top power vent picks
- Rheem Performance Plus Power Vent 50-gal
- AO Smith Signature Power Vent 50-gal
- Reliance 6-50-PVRT Power Vent
- Westinghouse WGRPV050 (lifetime stainless)
Bottom line
Atmospheric for homes with existing chimneys and no backdraft concerns. Power vent for homes without chimneys OR for tight homes with backdraft issues. Power vent adds $200-400 to equipment cost plus PVC routing labor. For chimneyless installs, power vent or sealed-combustion tankless are the gas options; alternative is to switch to electric heat pump.