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FHP Manufacturing AU035 Two-Stage Aquarius Heat Pump


Pros: Large area high flow air coil , stainless condensate tray, good sound damping, simple control with good LED status indicators, built in error detectio

Cons: Hot water recovery option is poorly designed and nearly worthless, pricey compared to less eff. models

I am not new to Geothermal heat pumps.  I installed a Florida Heat Pump  4 ton water to air heat pump in my home when I built it myself in 1978.  It was a single stage unit with a heat recovery unit to capture hot water from the waste heat in the summer.  I was able to turn off my electric water heater in May and not back on until late Sept. because the heat recovery unit supplied all my hot water needs.  The net effect was that summer cooling  was nearly cost free because of hot water savings. The unit gave me excellent service (for 30+ years) until now and needed replacing only because the condensate pan had completely rusted out.  I found it required periodic service due to well water quality and the freon charge had a small leak.  I had to add a sniff of freon 22 twice a year to keep it running efficiently.  I would not recommend water to air heat pumps to anyone that was not able to do minor plumbing and friendly with hand tools. 
I decided to replace the original unit with a more efficient model.  When I checked /calculated the heat cooling load for my 2000 sq. ft. house it came to 3600 BTU cooling and 2600 heating.  I took this opportunity to re insulate the duct work and add a thin insulating vapor barrier to the underside of the house.  The original duct insulation was sweating in the summer.

As a standard consumer I could find only a few choices for water  to air heat pumps for direct purchase for me to install myself.  The two choices were Florida Heat pump and Water Furnace.  The Florida HP unit was retail $7600 with freight for their top of the line 3600 BTU Aquarius.  The Water Furnace unit was $1000 more.  Since I had had good service from FHP in the past, I went with FHP.  Notice that I chose a smaller unit for the upgrade because I wanted to maximize summer time dehumidication.  The old system was never able to keep the humidity in a safe range in both summer and winter.  The hope was that the new unit combined with a carefully installed vapor barrier would keep the humidity in the 50% range.

I was able to beg a better deal on the FHP AU035 from a friend of a friend.  They suggested a Honeywell touch screen thermostat (this model usually only available installed by dealers) because it had more flex ability and has the dehimidification feature/settings and sensor.  Good advice.  I would not even have known about the high end therms. had I just shopped on line.

I now regret the FHP choice.  The hot water recovery unit was poorly designed.  It used a cheap circulating pump and a heat exchanger that was totally inadequate.  (My old FHP unit used high quality pump and coils).  The new recovery unit provides no significant hot water so I turned off that feature to keep the circulating pump from wasting power.  Something that I had not considered was that a scroll compressor adds/wastes less heat into the freon as it compresses the gas to liquid.  This contributes to the poor performance of the water heater feature. They could have compensated for most of the heat reduction by improving the quality of the heat exchanger.  (The freon hot side runs about 130 degrees F.  Still enough to supply domestic hot water.) 
 There was some sloppy layout and insulation that was not fastened.  Another stupid thing - they mounted the circulate pump (cheap pump) next to the controller and mounted the controller against the bottom of the pan.  When the pump leaks, there is nowhere for the water to go without creating havoc with the electronics.!!!! Pewwwww!
The Hone well thermostat was a delight.  I would not have guessed that the high cost could be justified.  Worth every penny.  It retails for over $700 but I paid $280 for my unit including the optional wireless out side thermometer/humidistat.

The new unit has run for five mo. with out any problem.  It rarely goes into full/high power which keeps it in the highest effic. (CEER 32)..  In low mode it draws less than 6 amps 220v.  That includes compressor, fan, and controls.  That does not include well water pumping power use.  The first stage of the two stage scroll compressor (Copeland) combined with a 12 speed fan reduces noise and energy use. Unlike some other manuf., the FLHP controller doesn't attempt to adjust the fan speed for max dehimdifiction.  This was a disappointment because all the hardware is there to do it.  Just needed a few more lines of firmware to do it right!  You can manually adjust the fan speed , but that isn't practical.  I will admit that the heat pump controller is otherwise well done.  They kept it small and simple.

Wish I had gone with Water Furnace but with so little information on the web, I took a chance with FHP not knowing that their quality had slid.  I hope my description will help someone make a more informed choice.  Let me know If I can help.




After a year, the unit crapped out with low pressure freon switch error.  It acted like it was low on freon.  After much checking I found that the TVX (thermal expansion valve) that automatically adjust the freon flow to improve effic. was not working.  It was choking the freon flow to the point that the 50 lb. low pressure switch stopped the compressor for protection.  The original TXV had a small leak in the sensing bulb.  I found a similar TXV on the junk market that was adjustable and designed for a 3 to 5 ton unit.. After I replaced the TXV and then found that the computer controlled fan was not changing speeds correctly.  This was fixed by using a diff. controller (part of the motor housing) that I bought from EBAY.  It is a plug in module on the end of the fan motor.  The bad fan control is why the heat pump would not control humidity.  Noe the system slows the fan down which makes the system ring out gobs of water at the evaporator.  The TXV also works better than the original and the system runs less.


It was a pain to have to cut out the bad parts, pump it down, flush with nitrogen, change the compressor oil to see if there was any junk in the oil, change the filter drier, and recharge the system.  Because I installed the system myself originally, I knew from the beginning that there would not be any warranty.  The repairs cost about $400 for the parts.  I added some sight glasses, valves , and extra freon ports to make troubleshooting easier next time.



FHP Manufacturing AU035 Two-Stage Aquarius Heat Pump

FHP’s Two Stage AQUARIUS goes beyond industry standards to bring you our highest efficiency unit together with the benefits of the new generation of environmentally friendly refrigerant. Available in Vertical and Counterflow models. Also available in either the ground water loop, water loop, or ground loop configurations (this will impact your capacity and your efficiency). All models are two-stage and can operate at either full or partial capacity (higher efficiencies can be achieved when operating at partial capacity). The specifications below are for the ground loop configuration operating at full capacity.

Energy Star QualificationYes
Energy Efficiency Rating (EER)17.2
Cooling Capacity38,000 BTUH
Heating Capacity28,000 BTUH
Coefficient of Performance (COP)3.8
Additional Features
Heating Seasonal Performance Factor (HSPF)
Release Date
Seasonal Energy Efficiency Ratio (SEER)
Model Name/TypeMPNEAN/UPC
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