I have a new house, with a 8 ton split (5/3) geothermal system, horizontal loops (8-125' loops), in the Pittsburgh area. The Carrier units are both in the basement furnace room, side by side, with the second air handler in the attic for the second floor.
We have gas hot water heater (80 gal). Both geothermal units have HWG in and out connections.
After reading as many posts here as I could find about the use of the geothermal for heating water, I still have a few questions:
1) is it cost efficient compared to gas? I understand it really would only be beneficial in the cooling season (I understand that pricing is against the rules, just wondering if it makes sense)
2) How big should the second tank be? 80 gal? 40?
3) Since I have two separate units, each with their own pumps and loops, is it possible to use both for the HW?
My setup is a 3 ton Waterfurnace split system. I have a 40 gallon NG water heater, and a 50 gallon electric as a buffer tank. After about a day of run time of the geo, the 50 gallon tank has 50 gallons of 130 deg water in it, and the geo actually shuts off the HWG pump.
My NG water heater is set for 120 deg, so the water going into the NG is higher than the thermostat. My NG water heater doesn't hardly kick in anymore. When the kids were all home from college, it would come on for a while, but since then, it just sits there waiting.
I never expected to be this happy with my geo system. Pleasant surprise I guess.
My setup is a 3 ton Waterfurnace split system. I have a 40 gallon NG water heater, and a 50 gallon electric as a buffer tank. After about a day of run time of the geo, the 50 gallon tank has 50 gallons of 130 deg water in it, and the geo actually shuts off the HWG pump.
My NG water heater is set for 120 deg, so the water going into the NG is higher than the thermostat. My NG water heater doesn't hardly kick in anymore. When the kids were all home from college, it would come on for a while, but since then, it just sits there waiting.
I never expected to be this happy with my geo system. Pleasant surprise I guess.
is it cost efficient compared to gas? I understand it really would only be beneficial in the cooling season
Cost depends on electric and gas rates.
DSH works in heating also and probably cheaper that non condensing gas would.
Tank size depends on hot water usage, but I would go no less than 50 gallon buffer tank.
You could connect both GEO units to one buffer tank
It takes a day to make 50 g of hot water with my geo. The buffer tank is there to preheat the water, to whatever it can, before it enters the NG waterheater. The performance is based on the outdoor temp.
This summer, it will probably be keep up just fine.
On days with little or no heating or cooling (spring / fall) primary water tank steps in and provides all domestic hot water. Geo with DSH only produces hot water in the course of heating or cooling the house
All summer long, when you would expect the hot water production to be the best, the water exiting my climatemaster was hardly warm. In testing with a digital thermometer, water entering the system was going in at 80-85 degrees and exiting at about 95 degrees. Small increase, so I am sure it is doing something, but no where near the 130 that some of the waterfurnace folks talk about. This was tested on 95 degree days in the summer when I would expect tons of heat being built up in the house.
We have two water tanks. Tank 1 sent to 130 degrees, tank 2 set to 95 degrees. The geo pulls from the bottom of tank 2 and feeds into the top.
I have called my installer and asked and they have told me "you can't heat all of your water with the geo"..
If someone else is having better luck I would love to know.
My neighbors on both sides have waterfurnace and both indicate that their hot water is noticably warmer in the summer, they assume because of the geo, than winter.
with all the geos i have put in.. i always put a 50 gallon or 80 gallon depending on size, electric marathon in there. the geo helps a little bit in the winter to heat it but in the summer has no problems. and the good thing with the marathons around here.. is the rec gives a lifetime warranty on them and they say you only loose 2 degrees of hot water through a 7 day cycle when your not there. i've noticed when people say they don't get enough hot water, sometimes i found the lines going to the water heater from the desuperheater are undersized.. mostly i see people run vanguard pex which is only 3/8" id and you really need 1/2" id so wirsbo is a good choice or just copper.
I have a 6-ton Waterfurnace unit with DSH. I have two water heaters: one is an 80 gal electric that is not energized -- it is simply used as a buffer tank (electric because it was inexpensive) and the other is a natural gas 50 gal.
The two tanks are connected in series. I have nothing to compare it to because my house is new and this is the setup I installed from the start. However I can tell you my holding tank is always hot in both the summer and winter.
My unit will supposedly halt DHW heating if the unit can't keep up with the house, however my DHW -- High Level indicator is on quite a bit... indicating the tempurate in the holding tank has reached the maximum temp. This tells me my unit is cranking out the hot water.
My natural gas water heater is set to a fairly low temp. Hot water coming into the gas heater means it does not work very hard. We have yet to run out of hot water.
My DSH draws from the top of the holding tank and sends the water back up through the drain at the bottom of the tank.
Plumbing Diagram for using old water heater as a nurse tank for NG water heater
I have a old water heater I am planning to use as a nurse tank for my NG waterheater off of my Water Furnace geothermal system but I cannot find a plumbing diagram for the setup. Does anyone have any suggestions.
1) is it cost efficient compared to gas? I understand it really would only be beneficial in the cooling season
The system uses a desuperheater for heat recovery water heating. As such, in cooling mode, it is only recovering waste heat that would be otherwise thrown away. There is no "energy cost" for this heat so it should compare favorably to a HW system that uses any paid-for energy regardless if the energy is gas, propane, oil, etc. The cost of the avoided energy is the savings, so it may be less with NG than other energy sources since NG is pretty cheap right now. But remember, you are comparing "free" to something that has a cost so of course there is a savings.
Note - in heating mode the water heating is not free. However it still leverages the COP of the heat pump so it can be 2.5-6 times cheaper than running an electric element heater, oil, or propane. Compared to NG heater, when used in heat pump heating mode, there may not be any significant savings. A detailed cost calculation would be needed to see if the desuperheater circuit should be allowed to operate when the HP is in heating mode.
Further note - there is a small electrical draw associated with the heat recovery circulating pump. In cooling mode this can be offset by a little lower head pressure/lower amp draw on the compressor so usually it does not really need to be considered, actually it’s possible to see a small net electrical savings in addition to the free water heating.
Something most people don't consider is that heat recovery water heating can be easily added to most any new or existing normal air conditioner, it doesn't have to be a geo unit.
All summer long, when you would expect the hot water production to be the best, the water exiting my climatemaster was hardly warm. In testing with a digital thermometer, water entering the system was going in at 80-85 degrees and exiting at about 95 degrees. Small increase, so I am sure it is doing something, but no where near the 130 that some of the waterfurnace folks talk about. This was tested on 95 degree days in the summer when I would expect tons of heat being built up in the house.
We have two water tanks. Tank 1 sent to 130 degrees, tank 2 set to 95 degrees. The geo pulls from the bottom of tank 2 and feeds into the top.
I have called my installer and asked and they have told me "you can't heat all of your water with the geo"..
If someone else is having better luck I would love to know.
My neighbors on both sides have waterfurnace and both indicate that their hot water is noticably warmer in the summer, they assume because of the geo, than winter.
just my $0.02
Every hwg system I’ve ever put in pulls from the top and feeds to the bottom and your buffer shouldnt have power to it. Sounds to me like the geo itself needs to be serviced check your he/hr to get a better view of operation.
Last edited by Pres1227; 05-17-2018 at 08:58 PM.
Reason: Wrong quote
is hot water hook up worth it?
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Originally Posted by djastram
Nest is POO!!