How to Size a CTS Cooling Tower: Model Selection Guide | CTS

Picking the wrong tower size costs money twice. Undersize it and your process water never reaches temperature, so your chiller works harder and your equipment runs hot. Oversize it and you have paid for capacity and fan horsepower you will never use.

This guide covers how to match a heat load to a specific CTS model. If you want the underlying theory first — what range and approach actually mean and why wet bulb matters — start with our guide to the four inputs that determine tower size, then come back here to select the model.

The short version: BTU divided by 15,000

Every CTS Model T-2 counterflow induced draft cooling tower is rated at 15,000 BTU/hr per nominal ton at 60 Hz.

So if you know your heat load in BTU/hr, the math is one step:

BTU/hr ÷ 15,000 = nominal tons

A 900,000 BTU/hr load divided by 15,000 gives 60 nominal tons, which is our Model T-260.

One important exception: on 50 Hz power, the same tower only rejects 12,000 BTU/hr per ton. If your facility runs at 50 Hz, divide by 12,000 instead. A 900,000 BTU/hr load at 50 Hz needs 75 tons, not 60.

Sizing from flow rate instead

Many people know their circulating flow rate but not their heat load. At standard design conditions, plan on roughly 3 GPM per nominal ton.

If you are circulating 240 GPM, you are looking at approximately 80 tons — the Model T-280.

This rule holds at a 10°F range. If your process drops water more than 10°F across the loop, the tonnage will differ, and it is worth sending us the actual temperatures rather than relying on the rule of thumb.

What “nominal tons” assumes

Every capacity figure on our site is rated at the industry standard design condition:

• 95°F hot water entering the tower
• 85°F cold water leaving the tower
• 75°F ambient wet bulb temperature

That is a 10°F range and a 10°F approach.

These three numbers matter because they are assumptions, not guarantees. Change any one of them and the tower’s real capacity changes with it.

Wet bulb is the one that catches people out

Wet bulb temperature is the lowest temperature air can reach through evaporation, and it sets the floor for how cold a cooling tower can get your water. A tower cannot cool water below the wet bulb, no matter how large it is.

The 75°F rating assumption is reasonable for much of the country. It is not reasonable everywhere. Summer design wet bulb along the Gulf Coast, through Florida, and across much of the Southeast runs 78°F to 82°F.

If your design wet bulb is 80°F and you size purely off the nominal tonnage table, your leaving water will be warmer than the 85°F you planned for. In practice that means either selecting the next model up, or accepting a higher cold water temperature.

Our Wet Bulb Temperature Guide lists design wet bulb by city. Look yours up before you commit to a model.

Worked example

A plastics plant in Macon, Georgia is running injection molding presses with a combined heat load of 1,200,000 BTU/hr. Water leaves the process at 95°F and needs to return at 85°F.

Step 1 — Convert to tons.
1,200,000 ÷ 15,000 = 80 nominal tons

Step 2 — Check the flow rate.
80 tons × 3 GPM = approximately 240 GPM. The plant’s pump curve confirms 237 GPM. Good match.

Step 3 — Check the wet bulb.
Macon’s summer design wet bulb is above 75°F. At 80 tons with a tighter approach than rated, the tower will run warmer on the hottest days of the year.

Step 4 — Decide.
For a process that tolerates a few degrees of variance in August, the Model T-280 at 1,200,000 BTU/hr is the right selection. For a process that cannot tolerate it, step up to the T-2100 at 1,500,000 BTU/hr and buy the margin.

That fourth step is a judgment call, and it is exactly the kind of thing worth a phone call before you order.

CTS Model T-2 selection table

All figures at 60 Hz, 95°F/85°F/75°F design conditions.

Model	Nominal Tons	Heat Rejection (BTU/hr)	Approx. Flow (GPM)
T-23	3	45,000	9
T-25	5	75,000	15
T-28	8	120,000	24
T-210	10	150,000	30
T-215	15	225,000	44
T-220	20	300,000	59
T-225	25	375,000	74
T-230	30	450,000	89
T-240	40	600,000	118
T-250	50	750,000	148
T-260	60	900,000	177
T-270	70	1,050,000	207
T-280	80	1,200,000	237
T-2100	100	1,500,000	296
T-2125	125	1,875,000	370
T-2150	150	2,250,000	444
T-2175	175	2,625,000	518
T-2200	200	3,000,000	592
T-2225	225	3,375,000	666
T-2250	250	3,750,000	740
T-2300	300	4,500,000	888
T-2350	350	5,250,000	1,036
T-2400	400	6,000,000	1,184
T-2500	500	7,500,000	1,481
T-2600	600	9,000,000	1,777
T-2700	700	10,500,000	2,101
T-2800	800	12,000,000	2,370
T-3000	1,000	15,000,000	3,011
T-3250	1,250	18,750,000	3,764
T-3500	1,500	22,500,000	4,516

Flow rates are nominal and rounded. Confirm exact figures against the model page or the Engineering Brochure before ordering.

Single cell or multiple cells?

A single tower works when your thermal load is steady year round.

Multiple cells make sense when the load swings seasonally or by shift. Two 40-ton towers instead of one 80-ton tower lets you shut one down during light load periods, which cuts fan energy, and it means a failure takes out half your capacity instead of all of it.

Redundancy costs more upfront. Whether it is worth it depends on what an unplanned shutdown costs you.

When the rule of thumb is not enough

Send us real numbers instead of a BTU figure if any of these apply:

• Your range is not 10°F
• Your design wet bulb is above 75°F
• You are replacing an existing tower and need to match a footprint
• You are running 50 Hz power
• Your process has tight temperature tolerance
• The load varies significantly through the year

Ready to size it properly?

Send us four things and we will confirm the model:

1. Flow rate in GPM, or total heat load in BTU/hr
2. Entering water temperature
3. Leaving water temperature required
4. Location — city and state is enough for us to look up your wet bulb

Request a quote or call 800-752-1905. We have been building fiberglass cooling towers in Macon, Georgia since 1971, and we would rather spend ten minutes getting the selection right than have you order the wrong tower.