If you have geothermal, I don't understand why your plumber hasn't come up with a better plumbing plan. Conventional tanked water heaters don't have any place in that picture, especially in new construction. You could possibly use a small tankless unit near the master to assist with filling your tub, but for the most part, the geothermal should more than take care of the rest of your home's needs if set up correctly. You really need to get a true plumbing professional involved here, and you need someone who is intimately familiar with geothermal.

I am thinking that it was done this way b/c we added geothermal after we're already had a plan in place and gotten started. Our builder said tankless would be much more expensive if we wanted to use it w/ geothermal? I mainly got the geothermal so I could run the a/c all the time w/o it costing tons and tons of money so we didn't really consider plumbing. We also have a radiant heat system w/ a separate boiler so we have geothermal, a boiler and a propane system.

I guess we need to look into it more. Does size of house matter as far as needing additional tanks or no?

When you set the hot water temperature lower or higher, you make the mixers valves use more or less of it to produce an equivalent flow. For this reason you will not get any precise answers today.

You need to put your plumber and HVAC contractors into a locked room and don't let them out until they come up with a plan. You certainly didn't need all of that overkill to heat/cool your home, and you don't need it to take a shower either. You're flushing money down that drain, and it's your GC's fault for not communicating better and having that powwow during the planning stage of the build.

Thanks live_wire_oak. I will see what can be done. We just added the second water heater last week and I think they are starting plumbing soon.

To be fair, it is kind of our fault too b/c I keep adding stuff. Our original contract and all plans were made w/o geothermal. We went to a home show and decided we wanted it and kind of sprung it on our builder. I do that a lot. We added the second hot water heater last week spur of the moment too.

the geothermal should more than take care of the rest of your home's needs if set up correctly.

This is not necessarily true. This depends on what area of the country you live in and how your system is sized (to save upfront cost and increase the ROI geothermal systems are often slightly undersized from the peak loads). In our area desuperheaters can only pre-heat the hot water before heading to the hot water heater. The highest they can heat the water is 90degF and that is only in the middle of summer. Our hot water heater then has to take it to 120degF. In the heating months the desuperheater barely heats the water if at all. The temperature of our well water is warmer than the antifreeze/water mixture leaving the heat pump coil. The whole concept of ground source heat pumps wouldn't work otherwise.

Beaglesdoitbetter, unless you live in an area that is never in the heating mode you need an additional hot water heater. But I agree with live_wire_oak that you should try to consolidate the hot water systems if you can. There is no need to have so many different units and different fuel types unless you have a large sprawling house where the water would get going from one end to the other.

Your builder is probably talking about needing to add a holding tank if you use a tankless water heater. A desuperheater is just a heat exchanger between the water/antifreeze mixture (it may be water depending on where you live) that is leaving your heating coil and the water line going to the hot water heater. Most knowledgeable installers will also add a holding tank between your heat pump and your hot water heater so that in times of high hot water use there will be plenty of preheated-fully heater water waiting. Typically this tank it is just the shell of another hot water heater with the guts removed (you want the tank to be insulated). Some installers try to get away with not adding this holding tank and the whole system still works because a traditional hot water heater is used. If you go tankless they are required to add this holding tank. Either way I would make them add it in. It shouldn't cost much more. A tankless will need a bigger fuel line though which may be another reason your builder was trying to steer you away from them.

three_acres- we do live in an area where heat is required. We are not using a tankless water heater b/c that cost too much for us when we are already WAY over budget. So we have the holding tank for the geo (50 gallon) and then another 50 gallon propane tank. Those will service most of the house.

We do have what I consider a big house (5000+ sq. feet not counting basement) although compared to some houses here, I guess that isn't big. The master bath is ALL the way at the other side of the house so that was why the builder and plumber suggested the 75 gallon tank to feed the master. There is also a washer/dryer in master closet. It was either the second tank or recirculating loop and for reasons I'm not clear on, the second tank was recommended instead and only cost a few hundred dollars more.

I'm nervous now that we don't have the right thing, so what you are saying makes me feel better b/c it makes it seem like our system makes sense.

1. "You really need to get a true plumbing professional involved here, and you need someone who is intimately familiar with geothermal."

+ 1

2. size ALWAYS matters - always

3. "For this reason you will not get any precise answers today" and other reasons too.

4. "I think they are starting plumbing soon. " - Better not until you have a sound plan in hand first.

5. 75 gallon tank will give you @ a 10 min. shower with one head & sprays and about 8 min. with both heads and the sprays. That's a big tub - how many gallons ??? 75 gal heater should be enough for it though. Be sure pressure and volume are high to that fill valve or you'll be waiting 20 minutes or more to fill it.

6. Be mindful of a cold water sandwich while showering if you are somehow tying in the two 50 gal tanks to the master bath plumbing for longer shower times. Again, back to design basics.

Thanks antss. What is a cold water sandwich, am I being dense?

The average fill on the tub according to MTI is 60 gallons. Fill to overflow (it's an overflow/infinity tub) is 130 gallons.

I will speak to builder/plumber again about what the plan is. I don't really care much for long hot showers since I prefer the tub, so it seems like I should be OK w/ the tub as long as I'm not regularly filling to overflow. We're going to do whatever we can w/ pressure. We're on well water but having several wells dug. It is also a remote-control filling tub w/ the radiant heat so I can always start it via its remote a little bit before I'm ready to take the bath and use the radiant heat to keep the water warmed in it. I think our other 50 gallon tanks will also tie in to provide backup water for the shower/tub too so that would give me 175 gallons total.

There are just 2 of us in the house, and we aren't going to be really using water for anything else during shower/bath times (I'm sleeping when DF showers, he's usually out when I take my long baths). If/when we have kids WAY down the line, we'll maybe have to add on more or something. Or not let them use hot water!

"What is a cold water sandwich, am I being dense?"

nope - it happens sometimes with on demand heaters in which the hot water shuts off for a second on then re-starts. Cold water flows and you get the blast from that "sandwhich" before the hot flows again. Remember the old days when some one flushed a toilet and you got a COLD SHOCK IN THE SHOWER ???

Depending on how you utilize the 3 tanks in different parts of the house you might get the same effect if one of the far heaters/tank has to push the cold water in the pipes out before it reaches the bath. This assumes that they are somehow triggering after the initial 75 tank is depleted. You can get around this with design, re-circ pumps and timers ect. , but just be sure.

Re: the tub - I'm not familiar with it (know the brand though) but if you want the infinity feature it's going to have to be full (130) and MTI is a bit dense with saying an average fill on that kind of tub is 60 Gal. I see their point - people won't fill it all the way every time - but doesn't that kinda defeat the intent of THAT tub ??? Might as well get a different (non-infinity) tub and save yourself a ton o/$$$. You can still go to the spa two or three times a year for the cascading bath if that's all you really use the feature.

Just be sure the system design is in place before proceeding, and once it is - Don't change you mind again.

Remember your multi featured shower is going to be limited time wise to 10 mins. or less with the 75 gallons, if you can tap the entire 175 gal. then you're pushing close to 20 minutes though - so that's respectable.

Thanks antss- I'm going to email the builder right now on how the backup tanks will work. The tub was picked before just about any other feature in this house, so I want to make sure it works right. 20 minutes for a shower also seems plenty long enough.

more good to know stuff:
One can deliberately set the water heater temperature at a scalding hot high temperature, and add a tempering valve to mix it with some cold on the way out of the tank. Then, it's still very hot, and you get a lot more gallons from your tank, useable throughout the whole house.

Key words to search :
Tempered Water Blending ; or
Tempering Valve,
Hot Water Mixing Valve,
Hot Water Extender Tempering Valve
Anti-scald Valve
Think of it as an industrial looking thermostatic valve with a single temperature output set once and for all. It extends the reach of your tank.

Well the heat pump desuperheater sounds like it is set up correctly. I would definitely consider 5,000sf a large house and with your bathroom plans the extra hot water heater makes sense.

With new construction wells I'd also recommend you install a whole house sediment filter for each incoming well pipe if you aren't planning to already. We have a Rusco spin down filter which is nice because you can clean out the debris without having to turn off the water. You'd be surprised how much debris fills up in the bottom of those tanks. Are you also trying to soften all that water? You would want that filter in front of any water softeners.

Thanks davidro. I will ask my builder about doing tempered water blending.

Three_acres, I don't know if we're doing a whole house sediment filter or not. We're doing a whole house water filter of some kind I think. (Can you tell how clueless I am, I only know about design of the house not any of what makes it actually function). We are currently not planning to do a water softener b/c DF doesn't like softened water. I guess we'll have to see how it goes. Hard/soft water is not something I know anything about, I've always just had water that works fine but I've never had well water either, so this will all be a learning experience for me.

They are the same thing. You can get varying sizes of mesh screen. Your plumber should know which one to order.

You can always add a water softener(s) later if hard water is a problem in your area. Nearby neighbors with private wells should be able to tell you roughly how hard the water is.