How to Size a Glycol Chiller for Your Fermenters

Undersize a glycol chiller and it runs flat out during a cold crash, never quite gets there, and your lagers ferment three degrees warm. Oversize it and you paid for a compressor that short-cycles all day. Sizing one is not hard, but it does take a few numbers. Here is the method we use when a customer asks which chiller to buy, with a worked example and a table at the end that maps it onto the chillers we sell.

Three loads, not one

A fermentation chiller has three separate jobs, and they do not all happen at once:

1. Holding temperature during fermentation. Yeast makes heat. A vigorous ale at high kräusen can climb 5 to 8°F on its own in a big tank. The chiller has to pull that heat out continuously for two or three days.
2. Cold crash. Dropping a full tank from 66°F to 34°F for clearing or lagering. This is the biggest single load and it sets the size of most chillers.
3. Ambient losses. Heat leaking in through the tank walls and glycol lines. Small on an insulated tank in a cool cellar, large on a bare tank in a hot garage.

Size for the worst realistic day: every tank crashing at once while one is still fermenting. Then add a margin.

Step 1: the crash load

Water needs one BTU to change one pound by one degree Fahrenheit, and beer is close enough to water. So:

Worked example, one 1 BBL Unitank holding 31 gallons, crashing from 66°F to 34°F over 24 hours:

31 × 8.34 × 32 ÷ 24 = 345 BTU/hr

Want it done in 12 hours? Double it: 690 BTU/hr. This is the first place people overspec. Nothing bad happens to beer that takes a day to crash, and a day halves the chiller you need.

Step 2: fermentation heat

A common brewery rule of thumb is around 280 BTU for every degree Plato of extract fermented, per barrel, released over roughly 70 hours. For a 15°P wort in a 1 BBL tank:

280 × 15 ÷ 70 = 60 BTU/hr averaged. Peak is two to three times that, so budget 150 to 200 BTU/hr per barrel at high kräusen. For a 10-gallon homebrew tank that is 50 to 65 BTU/hr, small, but it never stops.

Step 3: ambient losses

An insulated, jacketed tank in a 70°F room loses very little. An uninsulated stainless tank in a 90°F garage, held at 34°F, loses a surprising amount through the walls, and long uninsulated glycol lines add more. As a working allowance:

• Insulated tanks, insulated lines, room under 75°F: add 10%
• Bare tanks or lines, or a warm room: add 25 to 40%

Insulating the glycol lines is the cheapest capacity you will ever buy. Do it before you upsize the chiller.

Step 4: add it up, then add margin

Back to the 1 BBL example, insulated tank, cool room, crashing over 24 hours while at the tail end of fermentation:

Crash load	345 BTU/hr
Fermentation heat (peak)	180 BTU/hr
Ambient at 10%	55 BTU/hr
Subtotal	580 BTU/hr
Safety margin, 20%	115 BTU/hr
Chiller capacity needed	~700 BTU/hr

That seems small next to chiller ratings in the thousands, and for one tank it is: a 2,750 BTU/hr chiller can carry several. What pushes you up a size is in the next section.

Things the arithmetic misses

Ratings are at warm glycol

Chiller capacity is quoted at a specific glycol temperature, often 40 to 50°F, and it falls as the bath gets colder. To lager at 34°F you run glycol at 26 to 28°F, and at that setpoint a chiller delivers noticeably less than its headline number. Take 25 to 30% off the rating for lager duty.

Everything crashes on Friday

If you have three tanks, sooner or later all three want to crash on the same day. Size for it, or accept a slower crash on those days. A bigger glycol reservoir helps here: it stores cold when the chiller is idle and releases it when the load spikes. That is what the 17-gallon bath in our larger chillers is for, and why a BFT-67 buffer tank exists for bigger cellars.

Glycol mix

Use food-grade propylene glycol at 30 to 35% by volume. Less than that and it can slush in the bath at lager setpoints; more and it gets thick, moves slower and carries less heat. Never use automotive ethylene glycol anywhere near a fermenter.

Distance

Each chiller has a practical trunk-line length. Past it the pump cannot move enough glycol to carry the heat. Our compact chiller is rated to 75 feet of insulated line; the high-capacity models to 280 feet or more. Put the chiller near the tanks.

Which chiller: homebrew to 10 BBL

Or skip the arithmetic: our chiller sizing calculator does it for you, using MCED’s own sizing method. Capacities below are MCED’s ratings at 90°F ambient (80°F for the BEF-075).

Chiller	Capacity	Typical cellar (MCED rating)	Trunk line	Power
BEF-02	2,750 BTU/hr	One fermenter, on its single built-in pump. It doesn’t take extra pumps or a BFT-67.	75 ft	120V, standard 15A outlet
BEF-04	3,481 BTU/hr	Up to four tanks on their own pumps, 17 gal bath; up to ten with a BFT-67	130 ft	120V plug, 20A breaker max
BEF-05	4,440 BTU/hr	3 to 5 BBL pilot system, up to four tanks on their own pumps	280 ft	120V plug, own circuit (20A breaker max)
BEF-075	6,180 BTU/hr	5 to 7 BBL	350 ft	120V plug, own circuit (25A breaker max)
BEF-100	8,179 BTU/hr	7 to 10 BBL hall	450 ft	220V, NEMA 6-20 plug
BEF-150	12,900 BTU/hr	10 to 15 BBL hall	750 ft	220V, NEMA 6-20 plug

Chilling wort with glycol: two-stage knockout

Many small breweries knock out in two stages: city water through the first plate section takes the wort most of the way down, then glycol in the second section takes it to pitch temperature. Only that second stage loads the chiller.

Heat to remove: batch gallons × 8.33 × (temperature after city water − pitch temperature). A 1 BBL lager knocked out from 75°F to 50°F is 31 × 8.33 × 25, about 6,500 BTU.

That arrives in 20 to 40 minutes, far faster than a small chiller can remove it, so it comes out of the cold stored in the glycol bath and the chiller catches up afterwards. Two checks: the bath plus the chiller’s output during the knockout has to cover it without the glycol warming to within about 10°F of your pitch temperature, and the daily total, knockout plus fermentation, has to fit the chiller. A 17 gal bath covers a small ale knockout; a 1 BBL lager knockout needs the 67 gal BFT-67. The sizing calculator has a two-stage knockout option that runs both checks. In winter, city water alone often gets an ale to pitch temperature, and the glycol stage isn’t needed at all.

Connecting it to the tank

A chiller moves cold glycol. Something still has to decide when it flows into each jacket. On a Unitank that is the Fermenter Temperature Control Kit: a thermowell in the tank and a controller that switches that tank’s glycol pump, so each fermenter holds its own setpoint from the same chiller. If the chiller sits below the tank, choose the solenoid valve option so glycol can’t siphon back. One chiller, several tanks, several temperatures. The kit also converts the chiller's barb connections to tri-clamp.

Common mistakes

• Sizing for a 6-hour crash. Give it a day and buy half the chiller.
• Reading the BTU rating as a promise. It is a number at a warm bath temperature. Derate for lagers.
• Bare glycol lines. Pipe insulation costs less than lunch.
• Buying for today's tanks. If a second fermenter is a year away, buy the chiller with the extra pump ports now. Adding a tank to a BEF-05 is a pump kit. Replacing a BEF-02 is a chiller.
• Neoprene jackets on a jacketed tank. They trap condensation and do nothing a glycol jacket is not already doing. More on that here.

Not sure which row you are in? Send us your tank sizes, the beer you brew most, and the room temperature, and we will size it for you. Contact us.

How many fermenters do you need? Our free brewery capacity calculator works out barrels per year and the tanks it takes, then size the chiller for all of them. Opening a brewery? Start with how to start a nanobrewery.