Well tank for water tempering?

[MHM]

I am considering placing a tempering tank in the attic space above my garage to pre-warm my well water before the tankless hot water heater. It gets quite hot up there. I recognize that I could only use it for about 2/3's of the year but the house is used primarily during that time any way. I would have to drain and bypass the tank during the winter months. I will have a standard pressurized well tank in the system at all times. The tempering tank would be placed after the well tank.
I'm considering something like: http://www.homedepot.com/p/Water-Wo...tical-Retention-Well-Tank-ERTG42T-A/206780899
Water Worker Model # ERTG42T-A Epoxy Coated 42 Gal. Vertical Retention/Well Tank
I would probably go with the 82 gal version if they still make it.
Can I use a lower port for the water inlet and the top port for the water outlet?
Is the lowest port low enough to properly drain the tank in the winter?
Do I need to maintain any air in the tank?
If the water temp gets above my tankless HW heater set temp, will that cause any problems with the tankless system?
Do I have to worry about legionnaires disease with this setup? It could go a week or so at a time without any draw down. I've seen several comments about that online.
I realize the tank will probably sweat but no worse then the well tank before it.
Any other tank recommendation?

Thanks for your time.

 

[Valveman]

I am considering placing a tempering tank in the attic space above my garage to pre-warm my well water before the tankless hot water heater. It gets quite hot up there. I recognize that I could only use it for about 2/3's of the year but the house is used primarily during that time any way. I would have to drain and bypass the tank during the winter months. I will have a standard pressurized well tank in the system at all times. The tempering tank would be placed after the well tank.
I'm considering something like:http://www.homedepot.com/p/Water-Wo...tical-Retention-Well-Tank-ERTG42T-A/206780899
Water Worker Model # ERTG42T-A Epoxy Coated 42 Gal. Vertical Retention/Well Tank
I would probably go with the 82 gal version if they still make it.

If you connect a tank like that to the waterline going to the utility room, it will temper the cold water as well as the water going into the instant heater. You probably want to tee before the tempering tank. Then take one side of that tee to the cold water supply and the one that comes out of the tempering tank to the instant heater.

Can I use a lower port for the water inlet and the top port for the water outlet?

Yes you could, which would be best for getting out the warmest water.

Is the lowest port low enough to properly drain the tank in the winter?

No there will be about 6” below the lowest port than you can’t get out. But you could lay that tank in a cradle on its side so one port would be at the lowest point.

Do I need to maintain any air in the tank?

No air. You would actually want an air vent in the top to make sure the tank stays full of water without air.

If the water temp gets above my tankless HW heater set temp, will that cause any problems with the tankless system?

Those water heaters come on with flow. I do not know if they just don’t start if the water is already at the right temperature. If not the water would just be hotter and you would add more cold water at the tap to compensate.

Do I have to worry about legionnaires disease with this setup? It could go a week or so at a time without any draw down. I've seen several comments about that online.

I don’t know about “legionnaires”, but letting warm water just sit in a tank for long periods of time is not good.

I realize the tank will probably sweat but no worse then the well tank before it.

It will probably sweat more as it will have 4-5 times as much water in it as the well tank.

Any other tank recommendation?

If the instant heater doesn’t get the water hot enough, you probably just need a larger heater. Can you turn up the heat and not have to temper the water?

You could also just use a 50 gallon electric water heater with a low temp setting to temper the water. But then if you just give it a higher temp setting, you would not need the instant heater. Either the instant heater works or it doesn’t.

 

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[ThirdGenPump]

Over all it's not a good idea. Anything you put up there will have the side effect of being a dehumidifier, leaving water dripping off it.

If your going to do it anyway a tank have a low energy transfer rate as only water touching the outside is going to warm up. Your better off with a series of pipes, more like a radiator(if you want to go full redneck you could use an actual radiator).

If you want water that can melt your skin off, run it through a coil of black poly on top of the roof.

 

[Reach4]

I would add that tank to your sanitizing operation. https://terrylove.com/forums/index....izing-extra-attention-to-4-inch-casing.65845/ is my take on sanitizing -- maybe overkill.

 

[Valveman]

And remember an 80 gallon tank full of water will weigh 700+ pounds. Don't want it to come crashing through the ceiling.

 

[Craigpump]

Too much risk/aggravation/trouble for the minimal gain.

 

[MHM]

Thanks for the feedback. I don't have a hot water supply problem. So the tempering would be just to use some of the free heat in the attic during the warmer months. I'm not looking for the most efficient heat transfer but something that isn't too expensive to implement. If I do it, there would be a tee so the cold water isn't heated also and a bypass for the winter months where it would have to be drained. I still have the concerns about the warm/hot water sitting in the tank and at 80 gallons it would not get a real high turnover rate.

 

[Boycedrilling]

I think the coil of black poly pipe is the best idea.