Reducing number of hot water heaters

[revaldo29]

We purchased a home with 3 50 gallon electric water heaters dispersed throughout the basement. It’s a single story ranch home. All electric with no natural gas. First floor is large at 4300 square feet and the finished basement is an additional 2800 sqft. Basement has a drop ceiling so all plumbing is accessible. All the bathrooms (4.5) and laundry are on one side of the house and are serviced by two water heater. Two kitchens are on the opposite side ( one on main floor and one in the basement) wit their own water heater. We are a family of 5 and will have parents living with us in the basement for a short period of time.


I would like to reduce the number of water heaters to reduce operating costs and complexity. There is an unfinished basement space on the side of the house with all the bathrooms and laundry. I would like to replace the two heaters on that side with a single 80 gallon hybrid hot water heater and connnect the kitchens to it as well or keep a separate Conventional electric water heater on the kitchen side of the house. We live in Georgia so heat pump should work well to heat water most of the Year. From what I can tell, there are 3/4 inch main copper pipes with 1/2 pipes to the fixtures .

My main concern is time to get hot water. Currently all fixtures get hot water in < 10 seconds. By placing the hybrid in the unfinished space, two of the bathrooms will be approximately 45 feet away and the kitchens would be 75 feet.

Recirculating pumps from what I’ve been told don’t play well with hybrid water heaters as the heat pump can’t keep up with the radiant loss of heat on the water circulating in the pipes. Putting it on a timer or schedule is also not ideal with so many people in the house and a stay at home spouse.

May thought is to run .5 inch pex to the far fixtures to improve hot water delivery time and would appreciate input. Based on my novice calcs, I were to run .5 inch pex from the new hybrid water heater to the bathroom fixtures 45 feet away, I should get hot water there in < 20 seconds to the bathrooms which is reasonable. The kitchen with a 2.2 gpm faucet would take 20 seconds, also reasonable.

a heat pump water heater on my estimation would save about $300-400 with 5 people living in the house so seems like a worthwhile move if it can be done in a way that doesn’t compromise hot water delivery times.

 

[Jadnashua]

If the supply and return lines are well insulated, a hot water recirculating system doesn't need to waste a lot of heat due to radiation. Many of them are setup to only get warm water at the sensing point. That means hot isn't far behind, but also means less energy is lost to radiation.

It will depend on your use pattern whether a hybrid WH will work out for you. Their recovery time is slower.

 

[Sponsor]

 

[revaldo29]

What are thoughts about running pex to each of the dedicated fixtures? If I add the two kitchens, it will be a ~ 75 foot run of .5 inch pex to each kitchen. Two full baths and a half bathroom would be about 45 feet away

 

[Dana]

If the supply and return lines are well insulated, a hot water recirculating system doesn't need to waste a lot of heat due to radiation.

That's true even if insulated to the current IRC code-minimum R3 for both the supply AND return of a recirculation system.

A "demand" type recirculation system requires pushing a button to call hot water, but reduces the annual amount of heat abandoned in the recirculation loop.

What are thoughts about running pex to each of the dedicated fixtures? If I add the two kitchens, it will be a ~ 75 foot run of .5 inch pex to each kitchen. Two full baths and a half bathroom would be about 45 feet away

Many "home run" systems use 3/8" PEX to fixtures that don't need high flow. While 3/8" copper is limited to about 1.5 gpm (above which erosion becomes an issue) , 3/8" PEX is good for up to 3 gpm. There is a significant pressure drop at 45' at the full 3 gpm, but only about a 5 psi drop for 45' @ 1.5 gpm (low flow shower), and less than 1 psi for 75' @ 0.5 gpm (rinsing/cleaning stuff or washing hands in the kitchen sink). The drop per 100' at different temperatures can be found on page 3 of this document. (Multiply the head loss x 0.43 to get the psi drop. )

A flow of 1.5 gpm of tempered 120F water is plenty for a low-flow shower + handwashing basin, but not good enough for filling a tub. So the full bath with tubs would get half-inch, the kitchens & half bath can make out just fine on 3/8" unless you have a deluxe kitchen with multiple sinks or something. A clothes washer next to a slop-sink may want half-inch as well, but the washer alone usually doesn't.

 

[revaldo29]

That's true even if insulated to the current IRC code-minimum R3 for both the supply AND return of a recirculation system.

A "demand" type recirculation system requires pushing a button to call hot water, but reduces the annual amount of heat abandoned in the recirculation loop.




Many "home run" systems use 3/8" PEX to fixtures that don't need high flow. While 3/8" copper is limited to about 1.5 gpm (above which erosion becomes an issue) , 3/8" PEX is good for up to 3 gpm. There is a significant pressure drop at 45' at the full 3 gpm, but only about a 5 psi drop for 45' @ 1.5 gpm (low flow shower), and less than 1 psi for 75' @ 0.5 gpm (rinsing/cleaning stuff or washing hands in the kitchen sink). The drop per 100' at different temperatures can be found on page 3 of this document. (Multiply the head loss x 0.43 to get the psi drop. )

A flow of 1.5 gpm of tempered 120F water is plenty for a low-flow shower + handwashing basin, but not good enough for filling a tub. So the full bath with tubs would get half-inch, the kitchens & half bath can make out just fine on 3/8" unless you have a deluxe kitchen with multiple sinks or something. A clothes washer next to a slop-sink may want half-inch as well, but the washer alone usually doesn't.

For the 3/8" PEX to the kitchen Faucet that is 75 feet away, if I use a 2 gpm fixture, will I actually get 2 GPM of hot water so the wife can fill up a pot with hot water quickly? I guess I'm not clear on the difference between flow rate and pressure. The water will come out at 2 gpm but will not have as strong pressure due to the higher friction loss in the 3/8 inch pipe vs the 1/2 inch pipe? I can see where pressure in a shower might matter, but in practical terms for a kitchen sink where it's primarily used for washing hands, rinsing, and filling pots, pressure is not as crucial. Is my understanding correct?

Also, is 3/8 pex ok to the kitchen faucet if it will be feeding a dishwasher as well?

 

[Jadnashua]

Volume delivered will depend on the size of the pipe and the pressure at the point of use. There's friction in the pipe. The faster you ask it to flow, the more friction. The smaller the pipe, the more friction. The longer the pipe, the more friction. All of those factors can be seen in the design manual for the pipe you choose. INcreased friction means more dynamic friction loss. With no flow, the pressure (other than height differences) is the same everywhere in the system. Think soda straw versus a fire hose. You'll lose much less to friction on a fire hose than a soda straw. You have to know what your needs are, then decide what losses would be acceptable. If, for example, your supply pressure was on the low side, you may want to upsize the pipe diameter to minimize dynamic pressure losses. If you need a pressure reduction valve, a smaller pipe would likely suffice.

 

[Dana]

For the 3/8" PEX to the kitchen Faucet that is 75 feet away, if I use a 2 gpm fixture, will I actually get 2 GPM of hot water so the wife can fill up a pot with hot water quickly?

With 120F water @ 2 gpm there will be roughly a 15 psi drop over 75' of 3/8" PEX, and about a 4-5 psi drop with 1/2" PEX. Unless you are on a very low pressure potable system that does not present a practical problem. Even on a low pressure system if the flow dropped to 1.5 gpm (for about a 10 psi pressure drop) when filling a pot would anybody notice (or care)?

For reference, shower heads are flow-tested and specified at 60 psi. Most homes have at least 30 psi to work with.

Also, is 3/8 pex ok to the kitchen faucet if it will be feeding a dishwasher as well?

Dishwasher flow rates are about 1-1.5 gpm, with very intermittent and short draws- pretty tiny compared to filling a pot. Wouldn't sweat that one. If you happen to be filling a pot while the dishwasher is running it may exceed the continuous 3 gpm max spec for 3/8" PEX for several seconds, but the duty cycle is so low as to be inconsequential.

 

[revaldo29]

With 120F water @ 2 gpm there will be roughly a 15 psi drop over 75' of 3/8" PEX, and about a 4-5 psi drop with 1/2" PEX. Unless you are on a very low pressure potable system that does not present a practical problem. Even on a low pressure system if the flow dropped to 1.5 gpm (for about a 10 psi pressure drop) when filling a pot would anybody notice (or care)?

For reference, shower heads are flow-tested and specified at 60 psi. Most homes have at least 30 psi to work with.



Dishwasher flow rates are about 1-1.5 gpm, with very intermittent and short draws- pretty tiny compared to filling a pot. Wouldn't sweat that one. If you happen to be filling a pot while the dishwasher is running it may exceed the continuous 3 gpm max spec for 3/8" PEX for several seconds, but the duty cycle is so low as to be inconsequential.

Great, thank you all for the clarification. Running dedicated 3/8 and 1/2 pex to the far fixtures seems like the most sensible solution.