My water heater (GE Smartwater GG50T06AVG00; natural gas; 50 gallon) is over 18 years old and is no longer operating properly. I am strongly considering replacing it with a Heat Pump Water Heater (HPWH), most likely a Rheem ProTerra model. (My house already has a 240V/30A double-pole breaker labeled "water heater" with wires running to a junction box on the ceiling above the water heater, even though the current water heater needs no electricity. I suspect there used to be an electric water heater many years ago, but I have no way to confirm that.)

Unlike the old water heater, an HPWH needs a condensate drain, so I have to figure out where to route the drain pipe.

The water heater is about 2-3 feet away from my HVAC, which has three drains already: one for the AC Evaporator, one for the whole-house humidifier, and one for the high-efficiency furnace. However, the drains go to different places:

  • the furnace and humidifier drains go to a condensate pump which sends the water to the utility sink (10 feet up, 5 feet sideways, then 6 feet down).
  • the AC drain goes through a small trap and then a 25 ft pipe run to the exterior wall, where it drains onto the grass next to the house.

I think that I will need to hook the HPWH drain into one of those existing drains. The problem is that I don't know which one is better to use.

If I cut the AC drain (where it already passes the water heater) and add a tee to accept the water heater's condensate, I'm worried about (a) needing to add another trap (I don't know if code in Montgomery County, MD requires it - and the Rheem manual doesn't require it unless draining into a sewer - but I know that a HVAC installers on YouTube think it is unnecessary and can cause problems); and (b) the outdoor end of the pipe being blocked by ice in the winter.

On the other hand, if I go into the condensate pump, I'm worried about the pump being another point of failure. (The furnace is connected to the overflow switch on the pump so that it will shut down if the pump fails, but I would have to figure out if the water heater has a way to detect pump failure.)

One more part of the question - if I'm making changes to the drains anyway, does it make sense to change any of the existing drains (e.g. move the AC drain to the pump or remove the trap; move the furnace drain to outside, etc.)? As far as I know, the furnace does not have a condensate neutralizer (though the other three appliances don't need one) - should I use this opportunity to add one?

2 Answers 2


That's a fair-weather condensate drain

Here's the problem. I'm betting your air conditioning system is a non-reversible type that only ever runs in hot weather.

In the A/C season, it does not need to contend with the condensate line freezing and becoming blocked by an ice dam, does it? Using it for the water heater condensate drain year round would raise that as an issue.

Better to use the furnace dehumidifer drain.

The heat pump water heater is still cooking with gas

Heat pump water heaters heat the water by chilling something else. Generally, it's the air of the room it's installed in. That room will get super cold. What happens next depends on how your ventilation works. Either it will turn the room into a walk-in fridge, or it will chill the whole house. In summer that's a little less work for the A/C. In winter, your furnace will have to work that much harder and you'll have to pay for the extra therms of natural gas.

So you're spending natural gas on all the heat that goes into that water, at least all times but A/C season. Its vaunted "400-500% hyperefficiency" is stolen.

This is regrettable. We see many new "mini-split heat pump" systems which allow multiple "indoor heads" per outdoor unit. It wouldn't take a whole lot to create an "indoor head" which is actually a water heater - it'd be nothing more than a freon-water heat exchanger inside a tank. Then, it would simply be one of your heads (or the only head) on the outdoor unit, and you'd have the genuine efficiency they claim.

How much cool are we talking about? You can do the math yourself. 1 BTU is defined as the energy to raise 1 pound of water 1 degree F. (although, most furnaces and A/Cs say "BTU" when they actually mean "BTUs per hour").

8.3 pounds in a gallon, 415 pounds in 50 gallons (but you'll rarely use the whole tank). So if you raise water from 50F to 140F, then for each gallon used that's 750 BTU that will be stolen from the room. A shower might be 10 gallons so 7500 BTU.

  • You don't mean to claim that some new hyper-efficient, ultra-green technology is fudging their marketing claims, do you? That just can't be! </sarcasm>
    – FreeMan
    Dec 14, 2022 at 13:04
  • If it's installed in a basement most of the heat is actually coming from the ground. Mine has lowered the basement temperature a few degrees - no big deal, since the walls are all about 60F year round anyway. It's effectively stealing a tiny bit of heat through the insulation in the floor. The rest is 'free'.
    – KMJ
    Dec 14, 2022 at 15:56
  • And they make what you describe: the SANCO2 system and Chiltrix both do the mini split style water heating. Unfortunately they're expensive as they are still small volume products, which is a shame.
    – KMJ
    Dec 14, 2022 at 15:57
  • @FreeMan chuckle there certainly is dreck on any cutting edge, but this is not cutting edge. It's so mainstreamed that it became a government requirement in 2018 for tanked electric units > 55 gallons. Ill-considered "Red Barchetta" government overreach is actually rare in my observation, but this was a smoking gun case of it IMO. Dec 14, 2022 at 20:05
  • @KMJ yeah, they need to get it where it's a snap-in (MrCool) or plumb-in (Pioneer and other DIY) "indoor head" for similar inexpensive DIY-friendly outdoor units. Though obviously there'd be economies-of-scale advantages to having the heat pump do more than just heat water. Dec 14, 2022 at 20:07

For my install I went to the existing A/C condensate pump. I didn't worry about the additional point of failure for a few reasons. First: the condensate pump is already hooked to the A/C, so it will throw an error on the thermostat if it goes bad. Second: if condensate ends up on the floor in my situation it's not the end of the world, as it's an unfinished basement. You can judge your tolerance for risk here.

As to the second question about changing the drains, I wouldn't change them unless you already have a reason driving the change. Otherwise it's just redoing perfectly fine work.

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