Hayward HeatPro MCHX Series

The HeatPro MCHX Series is Hayward's microchannel line of HeatPro pool heat pumps, and it is six models: heat-only HP21105T, HP21205T and HP21405T, and heat-and-chill HP31105T, HP31205T and HP31405T, at nominally 110,000, 120,000 and 140,000 BTU. Two of the heat-only models are also sold online as W3HP21105T and W3HP21405T.

MCHX is Hayward's name for the microchannel air coil, which it calls an industry first. The part that touches the pool water is a titanium heat exchanger, and the compressor is a scroll running R-410A.

The manual also lists W3HP21205T and three HCB models, HCB1105T, HCB1205T and HCB1405T. Hayward's own site returns none of them, so they are not in the table above.

What 140,000 BTU becomes in cooler air

A heat pump's capacity is not one number, because it depends on how much heat is in the air it is pulling from. Hayward's manual rates every model at three conditions, and the 140K heat-only model runs like this:

• 80°F air, 80% humidity, 80°F water: 138,000 BTU/hr at a COP of 5.7
• 80°F air, 63% humidity, 80°F water: 128,000 BTU/hr at a COP of 5.5
• 50°F air, 63% humidity, 80°F water: 82,000 BTU/hr at a COP of 4.0

So in 50-degree air it still delivers a little under 60% of its warm-weather output, and each unit of electricity still moves four units of heat. The 110K and 120K models both fall to 75,000 BTU/hr at 50°F, which makes the 140K the heat-only model that keeps the most in cool weather.

COP is heat delivered divided by electricity used. A COP of 5.7 means the unit moves 5.7 times as much heat into the water as the electricity it draws.

Where it stops

Rated output at 50°F is not the whole story, because the air coil can freeze. Near 50°F air, the manual says, the defrost function runs to stop the coil icing, for anything from 15 minutes to several hours depending on conditions, and FS on the display means that is what it is doing. The heat-only models have no active defrost; Hayward lists active defrost only on the heat-and-chill models.

The manual's troubleshooting is blunter than its rating table. A heat pump that runs without heating in low air temperature should be left until the air exceeds 50°F, and an LP code from the low ambient cutoff should wait until the air reaches 60°F.

The air operating range depends on which document you read: 40 to 115°F in the manual, 45 to 110°F for the heat-only models in the brochure, and a 40°F minimum on Hayward's product pages. The practical reading is that it works in cool weather at reduced output, and it pauses, sometimes for hours, to defrost as the air approaches 50.

Flow, plumbing and the bypass

• 30 GPM minimum and 75 GPM maximum through the heat pump. The 140K is designed for 60 GPM. Above 75, the manual says, the pressure drop costs pumping energy, and a bypass is needed to hold flow in range.
• The manual's materials list is three 2-inch isolation valves, one 2-inch check valve and two 2 × 2 × 2 tees, and it ships with two union connectors for the inlet and outlet.
• An automatic chlorinator goes downstream of the heat pump, lower than it, with a check valve between them so concentrated sanitizer cannot drain back into the exchanger.
• A gas or solar heater must be plumbed in parallel and run one at a time, which the manual makes a condition of the warranty.
• The water pressure switch can be adjusted for a heat pump installed up to 6 feet below the pool surface or 15 feet above it. Outside that range an external switch may be needed.

When heating is not needed for more than a week, open the bypass and drain the heat pump. The manual warns that an exchanger left without circulation for more than 72 hours can be corroded by high chlorine gas.

The electrical side

The 140K runs on 230 V single phase and draws 8,300 W. The manual gives a recommended 50 A breaker, a minimum circuit ampacity of 42.5 A and a maximum overcurrent protection of 70 A. The 110K and 120K models are 40 A.

• A disconnect switch in line of sight of the unit is required. No junction box is needed at the heat pump; power lands on the contactor inside the control box.
• The unit is grounded and bonded separately, with at least No. 8 AWG solid copper from the bonding lug on its side.
• Below 208 V, damage may occur. The manual tells installers to make sure the voltage holds during operation.
• For automation, the heater takes a two-wire remote relay. Holding MENU and + until "bo" appears hands temperature control to the remote relay; holding them until "n" appears returns it to the heater's own set points.

Where it can go

It is an outdoor-only appliance, and the manual says not to install it in a garage, shed or other enclosed space, or under a deck.

• 12 inches of clearance around the sides, 24 to 36 inches at the service front, and 72 inches from the top of the unit to any overhang, which must be open on three sides.
• At least 60 inches from the inside wall of the pool, or 120 inches in Canada.
• Not within 12 inches of other outdoor HVAC equipment, and not where sprinklers or roof runoff can reach it.
• A level pad, because the coil drains three to five gallons of condensate an hour while it runs. Water under the unit is normal; the manual's test for a leak is to switch the heat pump off for several hours with the pump still running and see whether it stops.

Water chemistry, and the salt limit

The titanium exchanger is the reason this is a salt-pool heater, but the manual still sets limits:

• Salt 2,700 to 5,000 ppm. Above that it lists salt as corrosive to the heat exchanger.
• pH 7.4 to 7.6, total alkalinity 80 to 120 ppm, calcium hardness 200 to 400 ppm, chlorine 1 to 3 ppm.
• No tablets in the skimmer, and no chemicals poured into it.
• Municipal water only. The manual rules out mineral water and seawater above 5,000 ppm.

Damage from unbalanced water, sanitizer or low flow is not covered by the warranty.

Set points and start-up

On the heat-only models the pool set point goes up to 95°F and the spa set point up to 104°F, and neither goes below 50°F. Both are set to 65°F at the factory.

After switching on, the fan starts at once and the compressor within three minutes. After 10 to 15 minutes, the air coming out of the top should be at least 8°F cooler than the air around the unit; if it is not, the manual points to low ambient temperature or a component failure.

Winterizing

Hayward is explicit that the heat pump is not freeze protection and is not warranted against freezing. In cold regions it has to be drained when out of service: power off at the breaker, pump off, and open the lower inlet union to let the water out.

Where Hayward's documents disagree

• Capacity. The product pages say 140,000 BTU; the manual and brochure rate the HP21405T at 138,000 at 80°F.
• Air temperature range. 40 to 115°F in the manual, 45 to 110°F for heat-only models in the brochure, 40°F minimum on the product pages.
• Water connections. The manual says 2 inches, the brochure 2 × 2½ inches.
• Shipping weight. 281 lb in the manual and brochure, 250 lb on the product page.
• Low ambient restart. The troubleshooting chart says to wait for air above 50°F; the display code table says 60°F for an LP cutoff.
• Part numbers. The service parts sheet and Hayward's product pages disagree on nine numbers, and the sheet gives the compressor and fan capacitors the same one. Both are shown in the parts list.
• Cooling set point on the heat-and-chill models. One page of the manual gives a 55°F minimum for cooling, the next says heating and cooling both go down to 40°F.

Parts

Hayward publishes an exploded diagram for the whole series, though not in the manual. It's in the MCHX troubleshooting guide on the HP21405T product page, which reproduces Hayward's service parts sheet, 51300123201 Rev. D: 23 keyed parts and nine more not shown, with a column for each of the six models.

Most parts are shared across all six. What changes:

• 110K against 120K and 140K: the compressor (HPX51100101701 on the 110K and 120K, SMX11012755 on the 140K), the air coil, the fan blade and the top bracket.
• Heat only against heat/chill: the filter drier and control board, and the heat/chill models add a reversing valve and compensator.

Hayward's own product pages list a different number from the service sheet for nine parts, including the expansion valve, control board, water temperature sensor, fan relay and consumer kit. The list below gives the service sheet's number first and keeps the product page number beside it, so either can be quoted. The sheet also prints one number, HPX51401591801, for both the compressor and fan capacitors, which is almost certainly a mistake for one of them. Order by the full model number on the rating plate, as the manual asks, and let the distributor settle which number is current.

One year or five

The same heat pump carries very different cover depending on the prefix:

• HP21405T, from a dealer: five years parts and two years labor under Hayward's 2026 Expert Line terms, with the titanium tube covered for ten years.
• W3HP21405T, Hayward's Open Line: one year parts, no labor.

On a 233-pound appliance that needs a refrigeration technician for anything inside the sealed system, the missing four years and the labor are most of the difference. The Hayward brand page explains the two channels.