Allison, absolutely! The trick is often to convince your single-family trades to work off of plans and follow exact directions, instead of doing their typical thing.

Yes, we used up a good amount of 3/8″ pex on that house, don’t remember how much (in 2010), but I bet the savings on not having to buy and spend time crimping even a few brass pex fittings more than made up for that.

Paul, it sounds like you did a great job with that house. But there are actually four factors in hot water efficiency. The one you didn’t list was cost of the plumbing to set it up. With shorter runs, you use less material and need less time from the plumbers.

Kelly, yes, that can work and may be a good solution. Also, just because your kitchen is 40 feet away doesn’t mean the hot water pipe is only 40 feet. My kitchen is 40 feet from my water heater, but the hot water run to the kitchen is about 80 feet. It takes a trip around the house before it gets there.

Would it work to put an on-demand at the bath where the water comes in and let the existing water heater do the rest of the house? I ask because though I don’t have the 100 foot loop, this is my plan.

The water comes into the house at the bathrooms and that is where we replaced the original tank with a tankless but the kitchen is 40 feet away and the laundry is 10 feet beyond this so I have planned to put another water heater (maybe the heat-pump type to keep the pantry cool and dry) at the kitchen/laundry end.
I’m under the impression that we cannot use a recirculating pump because our rural water supply cuts off regularly and we get a lot of air in the line – I’ve read this kills these pumps. If there is a lot of air in the line, it is explosive!
Currently I use the (and please allow me this without ridicule) the clothes washer as a pump to pull hot water to this end of the house. I do a lot of laundry and can almost always use a few more gallons of water so it is less wasteful than sending it down the sink and faster too. The dishwasher heats the water itself. We have a gray-water system on this end of the house so this doesn’t affect the septic system.
I need to re-read the water-heating articles but while questions are being asked, I thought I’d get mine in: Will it work to put a second rectangle on this end and close off the pipe coming from the current system?
Thanks! Kelly

Don’t forget that IRC allows for 3/8″ piping to many fixture types, with limitations on pipe lengths. For that house the electric tank water heater was centrally located in a closet and we went with a central manifold in that same closet, with 3/8″ dedicated runs of pex to most fixtures (no fittings between manifold and fixture), except the washer being 1/2″, if I remember right. 3/8″ pex is a little over half the volume of 1/2″, and less than 1/3 volume of 3/4! That’s when we realized that hot water efficiency is about 3 things: user experience, heating cost, wasted water cost (while waiting).

Bathrooms in that house were laid out surrounding the WH closet. User experience was good, with wait time about 4s in bathrooms and one could not tell that those were 3/8″ runs. Kitchen sink was a bit further (maybe about 25′ of 3/8″ pex), but who doesn’t like to have a kitchen sink under a window? Again, you couldn’t tell that this was a 3/8″ pex run. Waiting on the homeowner to check the wait time for me again…

All of the above with water pressure set to 55psi in the house.

Nathan, electric POU for one shower would be a large electrical demand (10-15kw), a couple of those and you start impacting your electric service entrance size and if utility companies were to ever start demand charges on residential services then your utility bill will take a big hit too.

Michael, what’s the cost/payoff for hardwood floors or granite countertops? Yeah, I know, it’s apples and oranges, but reducing the length of hot water runs just makes sense. First, you get hot water faster. Second, the cost to install the plumbing is reduced because there’s less pipe to buy, install, and insulate. Third, less material and less energy use are the greenest way to go.

In existing homes like yours (and mine), it may be that the best solution is a demand recirculation system. A 100 foot long hot water line to your master bath is crazy long. I estimate my hot water pipe from the water heater to the kitchen sink is about 80 feet long. And it takes 2.5 minutes to get hot water there because the pipe is 3/4″ diameter all the way. Yours must be 1/2″, at least a good part of it.

Nathan, point-of-use electric tankless water heaters can work, but it wouldn’t be wise in a house with a lot of hot water use. The power draw can be excessive to heat water with electric resistance in a short time. Their best use is for one or two hot water fixtures far from the main water heater.

Dennis, minimizing the hot water rectangle ratio is mainly something to do with new homes in the planning stage. It costs next to nothing to spend a little extra time moving things around on a computer screen. Regarding different flow rates, that gets taken care of in right-sizing the pipes. See this article:

Why Your Hot Water Takes So Long

If you’re bound to an inefficient design of the hot water distribution system, either because it would be too expensive to modify your existing home or because you’re attached to the floor plan you already have, the next best option is to go with a demand recirculation system. I’ll cover that in a future article.

Jason C, if you’re talking about a continuous recirculation system, maybe with a timer, it can add a lot to your hot water bill. Maybe $50 a month just to keep hot water in the pipes. A demand recirculation system, on the other hand, reduces the pump runtime by 98 percent and the heat loss by 90 percent, compared to a continuous recirculation system according to Gary Klein.