Hot water flow tankless gas + electric tank + recirc loop

[Lzrsrgn]

I did not design this, but have to deal with it…

House is 8500 sf and has 6 full baths including master. Two laundry rooms .

issue is low flow. Main trunks are 3/4” but go down to 1/2” too soon.

will replumb main trunks to 1”.

Question is how to maximize hot water flow..

can run 1” cold to 2 parallel 3/4” tankless hot water heaters (Rinnai, no built in recirc). Can plumb 1” out. Issue is the electric hot water heater that serves as a storage tank… only has 3/4 in and out. Have a 1/2” recirc loop going to the tank so that hot water is always available, no wait on tankless. Thoughts?

 

[Fitter30]

Rinnai feeds the water heater with a recir line ? Have a spa shower or big bath tub? The biggest drop in the system is Rinnai call them with the complete model and get some gpm to pressure drop numbers. Have you ever checked incoming water pressure purchase a gauge with a adapter to hose in plumbing hook it up to a outside faucet if have a pressure reducing valve,softener and or filter measure at the wh tank drain valve.

 

[Sponsor]

 

[Lzrsrgn]

New Rinnais have a recirc pump built in, these do not. Rinnais feed Electric Hot Water tank which the feeds rest of house, recirc loop is on a separate pump which takes from hot water tank and returns to HW tank via 1/2” @ 1 GPM.

Yes, house has a Spa shower and big bathtub. Incoming house pressure is set to 90 PSI via PRV then goes through 3 big blue water filters in series (40”) with minimal pressure drop (to 80 psi). There are pressure gauges before and after each filter to tell what needs to be replaced and when. Don’t think it’s the Rinnais because they are linked electronically so when demand goes up they both fire on simultaneously (can provide up to 400,000 BTU.) When Bath AND shower are running simultaneously, pressure drops to about 35 PSI as measured by a PHYN after the water filters but before the 1” CW line feeding the rest of the house.

 

[John Gayewski]

What do you want to know. The smaller the pipe the more the friction loss on In pressure. Having small sections of 3/4" pipe isn't great, but it won't effect much.

It was pex before and your upsizing with more pex?

 

[Lzrsrgn]

What do you want to know. The smaller the pipe the more the friction loss on In pressure. Having small sections of 3/4" pipe isn't great, but it won't effect much.

It was pex before and your upsizing with more pex?

No PEX. All copper. Want to know if there is an electric water heater with 1” inlet and outlet (and correspondingly sized dip tube, or if I need to replumb the hot water main some other way to maintain flow rate. Bottleneck is the 3/4” inlet/outlet on the hot water heater.

 

[John Gayewski]

No PEX. All copper. Want to know if there is an electric water heater with 1” inlet and outlet (and correspondingly sized dip tube, or if I need to replumb the hot water main some other way to maintain flow rate. Bottleneck is the 3/4” inlet/outlet on the hot water heater.

The bottleneck won't hurt you for the 5' all that much.

A plumbing supply house near you would be the person to ask about a water heater with larger diameter inlet and outlet. They will likley sell you one, but it'll probably be a little more than you want to pay.

 

[John Gayewski]

Just rough numbers youd only loose 4psi per hundred feet of pipe at 8 gpm running 3/4" vs 1". So your 5 or 6 ft of 3/4 for the water heater isn't gonna lose your much. But I understand why you want it to be 1". You'd like to get everything you can. In this case I would probably leave the heater as is and change it later unless it really botheres you.

 

[Fitter30]

Model of ranniai water heaters 199k btu
Brand and model of the electric water heater
Page 86 5 gpm is 12 lbs

https://www.google.com/url?q=https://media.rinnai.us/salsify_asset/s-bb57a000-5f48-4159-ac3c-47e47f8180f7/100000467-N%2520Series%2520Residential%2520Condensing%2520Installation%2520and%2520Operation%2520Manual.pdf&sa=U&ved=2ahUKEwifruHBwKGFAxWGrYkEHZRaABkQFnoECAcQAg&usg=AOvVaw2MJff2Em5TpA7GyajIU_5O