ThermofennPlay Thermometers

How to play Thermometers

Fill some cells of each thermometer. Its round end is the bulb: a fill always begins there and continues along the tube.

  1. A thermometer can be empty, partly filled or full. Filled cells must form one continuous stretch from the bulb; no gaps.
  2. The number beside each row is the exact number of filled cells in that row. The number above each column does the same for that column.
  3. Mark every cell as filled or empty to finish. An unknown cell is still undecided.
Two four-cell thermometers. The upper one is valid: the first two cells from the bulb are filled, the last two empty. The lower one is invalid: an empty second cell separates filled first and third cells.××××Valid: fill begins at the bulbInvalid: an empty gap
Follow the tube even when it bends. A filled cell means every earlier cell back to the bulb must also be filled.

Start with a full or empty line

In a 4 × 4 puzzle, a clue of 4 fills the whole row or column. A clue of 0 means every cell there is empty. Then follow those marks along their thermometers.

If a cell is empty, every cell farther from the bulb must also be empty. These deductions still need to agree with the other row and column totals.

Mark cells

Tap a cell to cycle filled → empty × → unknown. A filled cell has a dot and a warm tube; an empty cell has a cross. Fill, Empty and Clear set the selected cell directly.

Arrow buttons select another cell. On a keyboard, arrows move, Enter or Space cycles, F fills, E marks empty, C or Delete clears, and U undoes. Tab leaves the board.

Undo reverses your last change in this tab. Restart asks before clearing the current board.

When you get stuck

Hint checks your current marks and offers one cell to fill or leave empty. If a mark blocks every solution, it offers to clear that mark first. Apply the suggestion or dismiss it; applied hints can be undone.

A check beside a total means that many cells are currently filled. It does not prove every thermometer is correct. The puzzle finishes only when every cell is decided and every rule is met.

Practice and Daily

Thermofenn has 24 original puzzles: twelve 4 × 4 and twelve 5 × 5. Daily selects from the same twelve-board set per size using UTC dates; boards repeat.

A new UTC day does not replace your current board. Your selected Daily date is remembered for each size across reloads. Choose Open today’s puzzle when you want to switch; the older saved record remains in this browser.

Progress is saved locally. If storage is blocked or a saved record is damaged, the game keeps the original and offers recovery options.

Continue in practice returns to your saved practice puzzle at this size. Next puzzle asks before leaving an unfinished practice puzzle with moves. Its saved progress stays in the collection; cycle through the puzzles to return.

Play Thermometers →