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The octopus in the basement.

Many older Alameda and Oakland houses were heated by a gravity furnace — a big round firebox with fat ducts rising out of it like arms. Some are still running. Here is what one is, and what replaces it.

Before and after

Same basement, a century apart.

Gravity furnace in a basement A large rounded furnace sits in the basement with three thick ducts curving up to registers in the floor above. There is no fan; warm air rises through the ducts on its own. Basement Floor above 1 2 3
Before: gravity furnace
  1. Big round ducts — often wrapped in asbestos insulation.
  2. No blower. Warm air rises through the ducts on its own, slowly and unevenly.
  3. Large floor registers; upstairs rooms often cold, no way to add cooling.
Modern furnace or heat pump air handler in the same basement A compact upright unit with a fan and a filter sits in the basement. A slim sealed trunk duct runs along the ceiling and branches up to smaller registers in the floor above. Basement Floor above 1 2 3
After: furnace or heat pump
  1. A blower moves air to every room, upstairs included.
  2. Smaller, sealed, insulated ducts — the old ones removed.
  3. A filter, and with a heat pump, cooling as well as heat.

Simplified drawings. Every basement and every old system is different; we look before we quote.

First: the asbestos question

The white wrap on old gravity-furnace ducts is often asbestos. Don't disturb it. Before we remove anything, the material is tested, and if it contains asbestos, a licensed abatement contractor removes it safely. We coordinate that step and only start once the basement is clear.

A new high-efficiency furnace standing in a clean, freshly painted basement, a slim sealed duct trunk above it
What replaces it

Three common routes.

High-efficiency gas furnace
In the old furnace's spot, with new ducts and a blower.
Heat pump with air handler
Heating and cooling from one system; no gas flue needed.
Ductless heads
Where the old ducts can't be reused and new ones won't fit.

Replacing an old system usually needs a permit; we handle it. Ask us about current utility rebates for heat pumps when you call.

An ornate cast-iron floor register set into the fir floorboards of an old Victorian parlour
Original registers can often be kept where the new ducts land.
A new sheet-metal duct trunk with sealed joints and branch takeoffs running along basement joists
New trunk and branches, sealed at every joint.
Homes

Victorians and bungalows

Gravity furnaces, floor furnaces and wall heaters replaced in older houses.

Businesses

Old buildings, too

Converted warehouses and storefronts with systems as old as the building.

Still running an octopus?

Book an inspection.

We'll look at the furnace, the ducts and the wrap, and explain the options.

Book an inspection (341) 214-5670
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