Adding a Water Heater

[crokett™]

Given the restrictions you’ve described, a second heater, maybe a size smaller at the far end makes most sense. Set it up as a stand-alone.

Thanks.

[MstrCarpenter]

So a 100' of 1/2" pipe holds about a gallon. You probably get about 2 gallons/ minute at the bath sink. So that should mean 30 seconds to get hot water, except you are losing some of the heat to the cold pipes, so you're wasting about 1-1/2 gallons at each "cold start." If you recirculated water back to the water heater, you might think that you now have to heat an extra gallon of water instead of dumping one down the drain, but that water is not as cold as the supply water so it won't take as much energy to bring it up to temp. That energy is equivalent to about 15-30 seconds in the shower. (In other words; a few cents)

If you installed a circulator on a return back to the water heater inlet using only a high/low temp. switch to control it, there would always be hot water at the tap, (as well as 2 gallons in the pipes) which is not efficient. However; if that high/low switch were powered by the bathroom lights, the pump would automatically turn on and there would be hot water at the tap in less than a minute, and when it did get there, the pump would automatically turn off. This arrangement solves the problem, saves water, and doesn't use additional energy (As compared to keeping an extra 10-20 gallons hot 24/7.)

[fixtureman]

I added a circulator pump and my bill didn't really go up

[Cabinet Monkey]

+1 on the recirc. pump. 

Faster , cheaper , easier to maintain.  And doesn’t waste energy all day like a tank heater.

[crokett™]

I have looked at a recirculating pump before. I understand the economics of running the water heater vs the recirculating pump. However currently we are interested in the added capacity of the second water heater, and it moves the source of heat about halfway to where it is needed.

[Bob10]

I have a few of these on the apts they seem to cut the wasted water down a bit and keep the tenants happy with hot water when they want it

https://www.amazon.com/Laing-LHB08100092...MDAK0?th=1

[crokett™]

Well after getting under the house and looking around at things and talking some more to my wife I think we are going to go with an electric tankless. It will be easier than I thought (I think) to pull the electrical. I also don't have as much headroom under the house in the ideal spot for the water heater as I thought. I will put the tankless water heater in the attic. I will plumb the existing one through it.

[EightFingers]

Remember with a tankless you have to flush it with vinegar once a year, so you need room to access the fittings to put a pump and bucket in. There’s also a filter that needs to be checked so don’t block that.

[crokett™]

I may create another thread for this, but my wife had all her clothes pulled out of the attic yesterday to switch from winter to summer. I took the opportunity to look things over for water heater planning. I confirmed there is an empty 3" PVC pipe that could be used as a chase. I know more or less how the 6 gauge power will be routed. The question is the plumbing. I thought (well assumed) that it was 3/4" lines feeding this bathroom. It isn't, at least not running across the attic. It's 1/2. I don;t remember when I was down in the crawlspace the other weekend whether it's 3/4 going up. Also both lines are white, not colored so I would need to figure out which is the hot. The attic is the area behind the kneewall. So it's maybe 5' wide, and about that high on one side and pitches down to the eave on the other. The plumbing comes up, runs behind my office to the bathroom. The bathroom is on the other side of the stairs from my office. There's room to squeeze behind the stairs in the attic, but it's tight. I did it once, years ago. I am wondering if it's worth pulling new 3/4" lines from the crawlspace. The idea would be pull new 3/4 lines from the crawlspace, get the heater hooked to those, then cut in the new 3/4 down in the crawlspace and up in the attic. I don't know if I can get to the first branch of the existing plumbing to the bathroom, but I can get most of the way there, certainly up to where the lines run behind the stairs. This also simplifies the plumbing because then all I need to do is reduce from 3/4 to 1/2". I don't need an unpleasant exploratory trip to figure out fittings, then another trip to tie things in. Is it worth pulling the new lines even if they only get most of the way there?

[blackhat]

Is there a flow problem up there now?  You trying to fix something that isn’t broken?  I would run a 3/4 line down the chase to use as a drain when servicing the heater.