Hi, I am new around here, and am impressed with the quality of the discussion at these forums. I tried the search function and could not find an answer to what I am interested in. I have a new housein NH. The house was finished in mid november. I have a ClimateMaster 5 ton open loop system for 2000sf of currently finished living space, and to accommodate the 1000 sf of basement that I am planning on finishing. Ducts are not yet in in the basement. The house is reportedly well insulated and tight, and energy star rated (I am still awaiting my paperwork on this). I have not yet received an electric bill yet here due to last month's ice storms. The heat pump has the hot water generator option, and this is attached to a single 80 gallon electric water heater. I live in the house alone. So one shower per day max on average. The dishwasher is run a couple times per week, and the washing machine a couple times per month. I also have a large whirlpool bathtub (111 gallon) with its own heater, which I will probably use less than monthly personally. I have not used the washing machine or tub yet, as I am still awaiting whole house water filtration. I have no natural gas, propane, or oil on the property. So my hot water concerns are these: 1. Am I wasting energy with a tank based heater? Should I consider a tankless electric hot water heater? 2. The hot water is not what I would call very hot. I don't know the exact temperature, but I can stand under the water run on full hot. It is not comfortable, but not scalding. Probably just meets the requirements for dishwashers and washing machines. This is probably good as my hot water needs are not high, and I am not over heating the water, but it doesn't stretch as far for my guests when I have 4-6 extra people here showering. Would a tankless water heater on a switch make sense for the extra demand for guests? Or should I turn up the water temp for when I have guests? 3. I need a hot water source in the kitchen that will drive an appliance that uses 2.23 gpm and only runs a few seconds at a time, a few times per day. Ideally, this would be immediately hot, as waiting for it to get hot defeats the purpose for this appliance. Additionally, this instant hot water might also be nice to use for hot drinking water for tea or instant oatmeal. So I am looking for a good point of use water heater recommendation for this small volume scenario. 4. For filling the large tub, though this would be done infrequently, is there any benefit to generating hotter water, or more hot water with a point of use, or whole house tankless, if the tub has a heater anyway? Thanks for any help with sorting this out.

I have yet to be shown any compelling data that proves tankless electric out preform standard tanked electric in heating dominant areas

in short yes the tank looses heat but it looses it to the house not up a flue, with space restrictions or point of use they serve a purpose

Just my opinion

Most all desuperheaters I've seen have some temperature adjustment on them. I have mine set at 125°F. The desuperheater feeds a Marathon 85 gallon water heater. This in more then enough hot water for 4 to 6 people. With outside temperatures below 30°F the duty cycle of my geothermal unit is high enough to supply all of our hot water needs. Per the Marathon installation manual, the lower heating element is disconnected for use with geothermal. I guess my point, your 80 gallon tank should be able to supply your needs, and if not, check the desuperheat out temperature setting and the water heater electric element heat setting. For tea hot water at the sink, they make point of use water heaters that will supply this. Most home improvement stores carry them.

Eric,  what brand heat pump do you have with a temp setting on the desuperheater?

My geo unit is an older Trane that the compressor was replaced with a late model Copeland scroll compressor. The desuperheater was added at the same time. The unit is made by Trevormartin Corp. The temp is set by adjusting a valve that controls the flow rate through the desuperheater. It came set to 120°F from the factor. I have adjusted it to 125°F. Regards,

i have posted a few times in the past about my system, i have a lttle experience with my system now and changed a few things. my 3-ton geo's desuperheater heats a 85 gallon marathon that is not wired in at all, strictly a preheat tank, the hot water out of the tank goes to a Tempra 29 on demand electric water heater. i initially had the desuperheater plumbed to draw water from the drain valve at the bottom of the tank and then return it to the top of the tank, first through the hot water line, then i changed it to the pressure relief valve. i observed tempuratures quite often to see how it was performing, i use a infared thermometer to measure the pipe temps, the problem with my first set up was, when there was a demand for hot water it was actually drawing some water through the desuper heater system, which eventually got cold as the bottom of the tank was filled with cold water, this reduced the water temps enough that my on-demand was cutting in to top up the temps. so i changed it to return the water to the pressure relief fitting, this eliminated that problem, however now, if somebody had a shower, there would be 5 to 10 gallons of cold water in the bottom of the tank, when the desuperheater turned on it would draw that cold water, add a couple of degrees to it and return it to the top of tank, cooling off the 60 or 70 gallons of hot water i had there, ruining the stratification. so i changed it once again, it still draws from the same place but now returns it into the cold water line. this works very well, tank stratification is always maintained, and as we speak the water coming from the top of my tank is 135 degres and the water being drawn from the bottom is 128 degrees. good thing i'm using wirsbo propex and not soldering!!

If I understand this correctly, your latest arrangement returns the water to the cold water line.  If so, then the returned water uses the dip tube in the Marathon preheat water tank to bypass the hot water at the top of the tank thus maintaining stratification.  I believe this arrangement is much safer and more efficient than using the water line from the Temperature and Pressure Valve.

I'm not a big fan of tankless electric heaters - they aren't much more efficient than standard storage tank electric water heaters (The highly touted savings comes when gas tankless is compared with gas fired tank models). A whole house tankless electric water heater requires massive electric service - up to 120 Amps, particularly in places such as NH where incoming cold water is relatively cold. They are expensive, utilize several very high watt density heating elements and frequently cycled high amperage contactors, both of which suggest to me lower durability and higher repair costs.

That said, Hedgehog's setup is good - for a desuperheater to work well it needs its own dedicated non-powered preheat tank. HH has been through the subtleties of plumbing the preheat tank as well.

Eric D - I believe I have experience with a thermostatically controlled desuper similar to what you describe - the thermostat serves as a lower, rather than upper limit on desuper outles water temperature. It can fix the stratification issue HH describes by preventing water from leaving desuper until it is well heated. That comes at a cost in efficiency - desuper recovers more, especially now with R410a systems, when it gets enough flow so it adds only 10 deg F or so 'per pass' several passes are needed to completely heat the preheat tank, but total recovered btus are higher.

A 1 or two occupant household might do better with smaller amounts of highly preheated water, and the thermostat setup would reduce the size of the required preheat tank - a slight cost savings and especially helpful in space sensitive installations.

A house with more people using much more hot water gains efficiency from greater total desuperheat recovery in the form of larger amounts of lukewarm water.

Assuming space and funds available, an ideal setup consists of separate powered and preheat tanks each sized for a day's typical hot water use.

Hedgehog, Not sure if you know about this or not, but the Marathon website has instructions on proper connection of a heat pump (desuperheater) system. Here is the link -> http://www.marathonheaters.com/cont_heatinstall.html Regards,

Engineer, Very informative writeup. In my case during the heating season the desuperheater can supply all of our hot water needs. Most times it is just my wife and I. The low loss of the Marathon water heater allows this. It takes about 18 hours of geothermal run time to top the heat level to 125°F mark to where the desuperheater will turn off. My tank is 85 gallons. Regards,

enigineer, your comments about electric tankless water heaters are correct, very heavy electrical requirments, mine is run of 3 50amp double pole breakers, plus because of cdn electrical code i had to have a 150 amp breaker on my main panel and then a sub panel with the 3 50's. and the unit it self cost me around $600, and they have gone up consideralably, search tempra 29 on fleabay. my reasons for going this route were mostly to do with our water, i am assuming it is the chlorine in our water, some people only get 2 to 3 years out of a normal hot water tank before they start leaking, ive been told 5 years is unbelievable. the Tempra is constructed with copper and brass, so it should last. and the marathon tank should last me quite a while, i tried ordering these items from my local plumber, they quoted me crazy prices, they want to keep these things out of town, because they make a fortune changing hot water heaters. i purchased my 85 gallon marathon in the US for half the price of a 40 gallon marathon in canada.

Eric D, no i didnt know about that info on the marathon site, thanks. i see it is identical to my set up, except the flow is reversed, i really dont think that will make any difference in performance, and actually i would rather have a pump draw from a lower elevation than a higher, if for what ever reason my water is turned off and there is service work being done and the hot water tank isnt full, if the desuperheater pump turned on it would be running dry, the other way unless the tank was completly empty there would be water. kind of a 1 in a million i guess. i'm glad i found out the hard way on how to plumb it properly, now if somebody asks me why i did it this way i can tell them exactly why.
we have been having a very cold winter so far, its -30 right now!! my Tempra hasnt cut in for months. just the way i like it, $1000 worth of water heating equipment doing nothing.
1 other reason i went with electric tankless is because i dont have natural gas hooked to my house.
my next project is to get my 2-ton water to water geo unit hooked up, heat my basment floor, garage floor, and then to complicate things even more, i want to use it to heat my marathon tank in the off peak heating/cooling seasons.
what i have in place so far is a 30 plate stainless heat exchanger with a Taco 007 plumbed in the same as my desuperheater, a Ranco ETC to control the marathon temps, a Taco 3 zone relay.

HH,

Thanks for the post. Real world experience always trumps the theory.