How to layout hot water pipes for the fastest hot water (or add recirc pipe)?

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orange_cat

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I am in a zone 5A. We are about to lay out pipes in a new construction 2.5 story house and I am agonizing whether to have a recirculation pump or just layout the pipes better? I dislike waiting for hot water, but it is really just the kitchen sink and the bathroom directly above the kitchen that are most used. I am attaching my diagram showing the potential layout (do not laugh - this is my layout). We are using copper L pipes. Everything is along a single exterior wall of the house - except for the laundry room, which is on the opposite wall. But the bathrooms and kitchens are in two vertical stacks (described from the ground up) One stak (left) - Water heater, 1/2 bath, 1 full bath (with a sink, shower, separate tub). Laundry room is the closest to this stack. The other stack is 1 bath (shower, sink), then kitchen, then main bath (double sink, shower, standalone tub).

(1) Is recirc pump my best option (I kind of like the simplicity of not having one. Fewer things to break? Fewer things to require electricity)?
(2) Can this layout be improved upon (narrower pipes? Different runs?)
(3) Would it make sense to run a dedicated line to kitchen sink and then to the upstairs bathroom (two sinks, then shower - tub does not really matter, it will eventually warm up).

Thank you for all opinions
 

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wwhitney

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In increasing order of immediate relevance, a few comments:

1) Best practice at the architectural design phase of the house is to layout out the hot water usage areas to be in a more spatially compact configuration.

2) Since the "right" stack is the one more commonly used, can you move the water heater to be next to that stack, rather than the left stack?

3) For recirc, on-demand is most energy efficient, i.e. push a button (or maybe use an occupancy sensor), and a pump at the remote end runs until hot water is available there. You could have two such pumps, in the upper bathroom on each stack. Or maybe just one on the right hand stack. You could have the ability to actuate the upper right bathroom pump from the kitchen.

4) If you're in a heating dominated climate, so that the waste heat from a timer based recirculation system (say run every 30 minutes or something) is not a loss for the vast majority of the year, then you could reconfigure the hot water system into one big loop and install a single recirculation system.

Cheers, Wayne
 

Reach4

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Consider running return lines during construction, even if you postpone actually putting in the pump and check valves. Both hot and return lines should be insulated. However running those in copper is more of a financial commitment than if those lines were run in pex.
 

orange_cat

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Thank you. Cannot move water heater as the right stack (beginning with the bathroom) is slab on grade - which is why the mechanical room with the water heater is where it is.
The stacks are actually compact - there is one on the left, then the staircase, and then the next stack. There need to be 2 bathrooms on the top floor and they are separated by the staircase only. And everything is within 8 feet from the outside wall.

If I understood both of you - it seems that recirculation is unavoidable?
The climate is weird - it is heating dominated for 7.5 months, but then it goes straight into AC season for 4.5 months. No in-between.
 

wwhitney

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If I understood both of you - it seems that recirculation is unavoidable?
It's a question of the performance you want. Given your layout, if I did the summation correctly the upper right double sink is 59 piping feet from the water heater. Best way to reduce the worst case wait for hot water would be to use a manifold system and run a dedicated 1/2" PEX line (*) to that bathroom. In which case the PEX line would hold about 0.6 gallons of water. So if you have a 1.2 gpm lavatory tap, you'd have to wait 30 seconds for hot water and waste 0.6 gallons of water.

Since you're using copper, the wait would be longer. I don't know if a 1/2" copper type L line would suffice for two bathrooms and a kitchen (probably undersize), but doing that would make it 25% worse compared to PEX. Make half of that 59 foot run 3/4" copper type L (up to dividing between the 2 bathrooms and the kitchen), and it gets 54% worse on top of that, so almost a minute to wait.

Cheers, Wayne

(*) I've never used 3/8" PEX, and I don't know if it would suffice to supply a full bath. But if it would, it holds only 55% the water of a 1/2" PEX line, and so the wait would be 17 seconds or so.
 

Jeff H Young

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Hands down Add Recirc! Way way better if you want CHEAP its another story and I dont trust any brainiac to calculate the true cost but haveing nearly instant hot water is a luxury to be appreciated in my opinion. if it costs 5 bucks a month or 4.55 7.01 I cant tell you but waitin a minute or more for hot water to come out of a water mizer faucet comes out to how many hours a year. and wasted water. plus its so darn nice to not wait!
 

joelcox

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In increasing order of immediate relevance, a few comments:


1) Best practice at the architectural design phase of the house is to layout out the hot water usage areas to be in a more spatially compact configuration.


2) Since the "right" stack is the one more commonly used, can you move the water heater to be next to that stack, rather than the left stack?


3) For recirc, on-demand is most energy efficient, i.e. push a button (or maybe use an occupancy sensor), and a pump at the remote end runs until hot water is available there. You could have two such pumps, in the upper bathroom on each stack. Or maybe just one on the right hand stack. You could have the ability to actuate the upper right bathroom pump from the kitchen.


4) If you're in a heating dominated climate, so that the waste heat from a timer based recirculation system (say run every 30 minutes or something) is not a loss for the vast majority of the year, then you could reconfigure the hot water system into one big loop and install a single recirculation system. I had a similar project in my architecture dissertation at the university, with a focus on the energy efficiency of the hot water system. During the project development, I utilized online resources related to architecture dissertation topics which greatly facilitated my research and data analysis. Additionally, as I had limited experience at the time, the service experts provided guidance on how to adjust the system based on climate conditions to minimize heat and resource loss throughout different seasons.

Cheers, Wayne

Could you please confirm if I understand correctly that the best choice for Atwater, MN would be to install a single timer-based recirculation system?
 
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Reach4

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I doubt that he would think a timer-based system would be better than a sensor-based system or a push-a-button system.
 
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