Last Updated on September 13, 2026
How to Build a Cheap Maple Syrup Evaporator on a Backyard Fire Ring
I wanted to boil sap from my sugar maples without buying an evaporator. I had seen cinder-block evaporators online, and I already had a fire ring in the yard, so I built the evaporator inside it. It burned efficiently and boiled fast. Here is exactly how it went together.
What you need
- An existing metal fire ring.
- Concrete blocks: two to set inside the ring as the base, plus eight solid concrete blocks stacked four per side to form the walls the pans sit on.
- One concrete block with a hole in it, for the chimney.
- A 3-inch stovepipe for the chimney.
- Two flat pans for the sap (I used two evaporator pans; large steam-table pans also work).
- A few small blocks to close gaps and keep the draft in the firebox.
How it goes together
- Set the two blocks inside the fire ring.
- Stack the solid blocks along each side, four high, leaving the firebox open between them. The two pans bridge the walls.
- At the back, use the block with the hole and push the 3-inch pipe through it as a chimney. Add small blocks around it to close the gaps.
- Light the fire in the front. The chimney at the back pulls the flames under the pans and out. With the 3-inch pipe the draft is strong and the sap gets to a rolling boil quickly.
Why the draft matters
Without a chimney the heat rolls out the front. With the pipe at the back, the fire pulls through the full length of both pans, and that is what makes a small furnace out of a fire ring.
Finishing
I finish the syrup indoors on the stove where I can control the temperature, and check it with a hydrometer. Use the Maple Sap to Syrup Calculator to see how much sap you need for the syrup you want.
