Why Neoprene Jackets Are Unnecessary for a temperature-controlled jacketed conical fermenter
A jacketed fermenter controls its own temperature, so a neoprene jacket is usually unnecessary. Here is when insulation helps, and when it just gets in the way.
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The short answer: for most homebrewers, no. On a jacketed fermenter, the glycol or water jacket does the temperature control, and the controller runs it only when the beer needs it. A neoprene jacket is passive insulation: it can’t cool or heat anything. It only earns its place when you hold a tank near freezing in a warm room, where it cuts chiller run time and stops condensation dripping on the floor.
| Situation | Neoprene jacket? | Why |
|---|---|---|
| Ale at 64–68°F (18–20°C), room at 65–75°F | Not needed | The beer is close to room temperature; the jacket only has to remove the heat of fermentation |
| Lager at 48–52°F (9–11°C) | Optional | The chiller runs a little more without one; the beer is still held on target |
| Cold crash or lagering at 32–35°F (0–2°C) in a warm room | Helpful | Less chiller run time and far less condensation |
| Fermenter in a cold room | Won’t fix it | Insulation slows heat loss but can’t add heat; move the tank somewhere warmer |
What actually holds the temperature is the jacket, a thermowell probe in the beer, and a controller. That’s our fermenter temperature control kit on a jacketed Unitank.
What holds the temperature
The controller reads the beer through a probe in the thermowell. When the beer drifts above the setpoint, it opens a solenoid valve on tap water or switches on the glycol pump, and coolant flows through the jacket until the beer is back on target. Then it stops.
For an ale, most of the heat it removes comes from the yeast. Fermentation makes its own heat, most of all in the first few days (see what makes a fermenter heat up). A neoprene jacket does nothing about that heat. It only slows the heat coming in from the room.
When insulation helps
Heat leaks through the tank wall in proportion to the gap between the room and the beer. In a 70°F (21°C) room:
- An ale at 66°F (19°C) has a 4°F (2°C) gap. Almost nothing leaks in.
- A cold crash at 34°F (1°C) has a 36°F (20°C) gap, nine times as much, for days or weeks.
That second case is where a jacket pays for itself. The chiller runs less, and the tank stops sweating. Any surface colder than the room’s dew point collects condensation, and a crashed tank in a humid summer basement can leave a puddle under it.
When a neoprene jacket gets in the way
- Ports. It has to fit around the jacket inlet and outlet, the thermowell, the sample valve and the racking arm, and it hides a weeping fitting until there’s a puddle.
- Moisture. Condensation that gets under it stays there. Take it off and let the tank and the jacket dry between batches.
- Fermenters without a cooling jacket. On a plain fermenter, insulation keeps the heat of fermentation in, so the beer can run warmer, not cooler.
Cheaper ways to cut chiller run time
- Insulate the glycol lines and fittings. They pick up heat and drip condensation, and foam pipe insulation is cheap.
- Pick a cool spot. Keep the fermenter out of direct sun and away from anything that blows warm air.
- Don’t run the glycol colder than you need. Colder glycol means more condensation and more swings past the setpoint.
- Size the chiller for your coldest job. Use the sizing calculator on our glycol chillers page.
- Save the neoprene for crashes and lagering in summer, if you want it at all.
Frequently asked questions
Do I need a neoprene jacket to cold crash?
No. The glycol jacket gets the beer cold on its own. The neoprene just means the chiller runs less and the tank doesn’t drip. See cold crashing.
Can I cold crash with tap water through the jacket?
No. Tap water can only cool the beer to a few degrees above the water’s own temperature, and insulation doesn’t change that. For crashing and lagers, you need glycol.
My fermenter sweats. Is that a problem?
Not for the beer. It’s water from the room’s air condensing on a cold tank. Put a tray or towel under it, insulate the lines, or add a jacket if it bothers you.
Can the jacket heat the beer?
Our kit is set up for cooling. Fermentation makes its own heat, so most setups only ever need to cool; in a cold room, move the fermenter somewhere warmer.
Related guides
Setting up a fermenter temperature control kit, how to size a glycol chiller, what makes a fermenter heat up and cold crashing. Find the right chiller with the calculator on our glycol chillers page.