Why Your Old Gravity Furnace Should Be Replaced
Many pre-war SF homes still run an octopus-style gravity furnace. They're simple and durable — but inefficient, hard to zone, and worth planning to replace.
- Author
- By Cabrillo Plumbing, Heating & Air
- Last updated
- Updated June 2026
- Reading time
- 4 min read
A gravity (or 'octopus') furnace heats by natural convection through large round ducts, with no blower. They can run for decades, but they waste a lot of energy, can't filter air well, and leave upstairs rooms cold while the basement bakes. When one needs major repair, a modern furnace or — better in our climate — a heat pump is usually the smarter long-term move.
What to know
- No blower means uneven heat and no real air filtration for allergy or wildfire-smoke season.
- Old asbestos duct wrap is common on these systems — never disturb it; have it assessed first.
- Replacing opens the door to zoning, better filtration, and electrification (a heat pump).
- Plan replacement before a cold-snap failure forces a rushed decision.
Full guide coming soon
This is the short version. A deeper, fully-cited guide for San Francisco & Peninsula homeowners is on the way. Need an answer now? Ask our team or call (415) 843-2900.
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