Looking at Honeywell mixing valve

[KULTULZ]

Originally Posted by LiQuId

...and everybody thinks us plumbers are just turd herders.... lol

No Sir!

I have much respect for your craft. It has to take you guys years to gain the knowledge you must have. It's just the sloppy ones that bother me...

[LiQuId]

thank you good sir... the sloppy ones bother me too, but Do keep me buisy with repairs.

[PDubs]

Wow!! I asked for the math and sure got it! That was truly enlightening and I appreciate the time and effort you took to explain what's happening "behind the scenes." I knew some level of calculations had to go into designing the best system but obviously was unaware of all the intrinsic variables.

Your very first statement stuck out at me: Delta T will change as the season does. I've heard that source water impacts overall hot water but have never understood how much. This is usually conveyed from the manufacturers as basically saying if it's colder out, expect less hot water, which sounds like a standard, blanket statement to me. Or at least that's what AOSmith gave me as a response.

Current temperature forecast is below
- Monday: 70/47 F
- Tuesday: 62/53 F (precip 70%)
- Wednesday: 59/44 F (precip 90%)
- Thursday: 63/43 F (precip (40%)
- Friday: 71/43 F

Electric tanks are it. The house was originally designed to have two water tanks with a recirculating pump as you mentioned, but budget constraints and the fact it's only me and my wife indicated one should be enough. Desired time for shower is minimum 15 minutes, although if my wife could get 20 minutes so she could massage her back believe me, she would do it.

Again, I can't stress enough how much I appreciate your time with troubleshooting our issue or perceived issue.

[LiQuId]

15 mins x 6gpm = 90 gallons needed for a shower, are you sure its 2 gpm from each head? this is a large amount of water.

the obviouys and cheapest way to extend the hot water is to use less, either by using different heads with less flow or by use of flow restrictors.

21 gph recovery on your current tank
21 / 60 = 0.35 gallons per minute recovery.

so, in essence you are using 6 gallons per minute and recovering less than 1, which tells me another tank may not be enough alone to recover what you are using and the temperature would still drop off towards the end of your shower.

My recomendation would be to install a storage tank and a circulator, though I have never heard of this being done with an electric tank, though I suppose it is plausablle it would also cause the electric bill to be large and extend stress upon the current heaters components, namely the heating elements.

increasing the temperature would help to extend the shower but it may still be marginal.
I would consider a real world test just cranking the temps up on the hot water tank you have ( considering it sounds like this is not a system you;re looking to invest to much into ) take the top element up to 150 and either keep the lower one set for 140 or just sliightly more. be aware that the supply water has been increased to this now and the risk of scalding at the fixtures increases with it. this would be the reason for installing a thermostatic mixing valve on the hwt outlet.

if you say you are getting 9 mins with one tank then without even doing the math one could reason that you should yelid 18 mins with 2..... though gas tanks will always be a better value for both amount aof water availablle and cost of fuel to heat .

[LiQuId]

http://www.pexsupply.com/AO-Smith-GCVX-50-50-Gallon-ProMax-High-Recovery-6-Yr-Warranty-Residential-Water-Heater

here is a link to a similar hwt that is natural gas, look at the recovery rate 67 gallons per hour

67 / 60 = 1.11 gallons per minute.. still not enough to recover as quick as you're using it, but your shower would stay much hotter for much longer without having to oveercome as much temperature loss as in the electric model.

[LiQuId]

http://www.pexsupply.com/AO-Smith-GDVT-50-50-Gallon-ProMax-Direct-Vent-Residential-Water-Heater

another link to a direct vented hot water tank...
I have looked into it and all electrics seem to have a 21 gallon per hour recovery rate.

[phishfood]

You ARE bored, Liquid!

[LiQuId]

broken leg.... yup, can only do so much around the house stuff.