Tankless heater with holding tank at point of use idea with schematic

[Scootersyme]

Hi all,
Long time reader first time poster! I'm a General contractor and have over the years installed several radiant and domestic hot water systems using tankless hot water heaters. After installing these systems and I have one myself, noticed that although they are efficient and work well the time to point of use can be a bit of a nuisance as it takes some time to get that hot water to point of use. Hit the faucet or shower, tankless unit senses, then depending on the distance to POU it can take over a minute or more for hot water... 1st world issues I know we should be so unfortunate!

I am building a house and was dreaming of something I thought would eliminate this problem without a lot of cost or heartache and was wondering if any of you pro-plumbers would be willing to take a look to see if I am on the right track with regard to technical issues that might be avoided. I want to place a small hot water holding tank... say 5 gallons in the attic (Well insulated) That is heated via a tankless water heater through a controlled thermostatic controlled recirc loop. The tank would give almost instant hot water to the POU until the tankless heater was able to "Catch Up" and take over. I have attached a schematic of how I thought this might work and would much appreciate any input as to how to make this something that would work in the real world.

Thanks kindly in advance

 

[John Gayewski]

Huh? Navien has a holding tank (inside of it) and can be recirculated at full temp. There's no reason to wait for hot water unless you pipe it in a way that makes you wait. There's even a circulator inside of the unit. Your can program run times and what not our just have it learn you habits and circulate accordingly.

 

[Sponsor]

 

[Breplum]

I agree, Navien is my choice. Noritz also has condensing units with built in pump but no mini tank.

 

[Fitter30]

Taco pump wouldn't go back into the hot line would go back recir fitting in the heater. Hot water line bypassing the water tank don't need it. Tank in the attic bad idea what would happen if power was out in your coldest weather for day or longer. Electric water would make a good storage tank plus if it's wired in the element would just maintain temp since hot water feeds it.

 

[John Gayewski]

Electric water would make a good storage tank plus if it's wired in the element would just maintain temp since hot water feeds it.

You can't use a tank heater with a tankless heater. The tank causes the tankless to short cycle and kills condensing.

A dumb tankless with no brain and a flow meter set above the flow of the recirc pump could possibly work, but that's not realistic.