Will CSV and regular pump play nicer with tankless water heater then my scala2

[Personalt]

I have a house in an area that uses a water tower for pressure and pressure at lower floor is 20-22 - psi. I wanted to bring the pressure up to a more normal 50-60 so my tub doesn't take 25 minutes to fill. I started with a scala2 and it worked well enough with high demand but with low demand (single sink fixture) it acted more like a pump on a 40/60 pressure switch and would cycle a lot. It was like it the slowest the pump could run was too fast. The core issue of the cycling was that when it hit 60 psi and cycled off it would fool my tankless's flow sensor and have it throw a low flow error for a few seconds while pressure is dropping causing there to be no hot water. Scala2 is being shipped back today.

1)It seems like a basic pump with a CSV would equalize the pressure and flow past tankless flow sensor to prevent tankless heater from shutting off when there is small demand. My only concern is that if my flow is less then 1 GPM then CSV would start filling the tank which means it will eventually get to target pressure and then shut off. The scala2 has a very small built in tank. I was wondering if the more reasonably sized tank with CSV would cause the pressure bleed off to be slower and stop the tricking of tankless flow sensor on low demand

2)How do I size a pump for this? Any recommended pump? As said above I have about 20-22 psi. It is a shore house with 2 outdoor showers, 4 indoor showers/bathrooms, 2 kitchens and 2 washers. In short term, would this pump be okay to play/test? Lowes has a much better return policy then my plumbing supply and I could likely find another use for this lowes pump if the CRV and tankless dont play nice. Or if they do play nice together i can reuse this pump and then buy a more quality pump. https://www.lowes.com/pd/Utilitech-1-HP-Stainless-Steel-Lawn-Pump/1000678113

 

[Personalt]

Tagging @valveman to see what advice he has

 

[Sponsor]

 

[Valveman]

Yes the CSV as comes in the PK1A kit makes tankless heaters work perfectly. As long as the pressure stays 50 PSI constant. the flow through the shower or faucet will stay constant, and the heater won't shut off. But if it goes 40 to 60 the flow changes and the heater shuts off. With a jet pump and 20 PSI coming in the CSV1A will have a minimum flow of about 0.5 GPM. As long as your faucet or shower is using more than 1/2 a GPM, the CSV will hold the pressure at 50 PSI steady. However, you will have to use the water out of the pressure tank as the pressure drops from 60 to 40 before the pump will come on and the CSV can start to work. With the 4.5 gallon size tank only holding about 1 gallon of water the drop from 60 to 40 happens fairly fast, the pump comes on, and the pressure hits 50 and stays there. With a 3 GPM shower this all happens in about 20 seconds and you are at 50 PSI. With a 0.5 GPM sink faucet the pressure will decrease for 2 minutes before the pump comes on.

A lawn pump or sprinkler pump does not build enough pressure to work with a pressure switch. You need a jet pump. A 1/2HP like a Goulds J5S would be best, but there are some really inexpensive versions of jet pumps as well. NT has a Drummond with tank and switch already mounted. Adding a CSV1A is not that tricky as many have done it. Don't think they last long but....

 

[Personalt]

Yes the CSV as comes in the PK1A kit makes tankless heaters work perfectly. As long as the pressure stays 50 PSI constant. the flow through the shower or faucet will stay constant, and the heater won't shut off. But if it goes 40 to 60 the flow changes and the heater shuts off. With a jet pump and 20 PSI coming in the CSV1A will have a minimum flow of about 0.5 GPM. As long as your faucet or shower is using more than 1/2 a GPM, the CSV will hold the pressure at 50 PSI steady. However, you will have to use the water out of the pressure tank as the pressure drops from 60 to 40 before the pump will come on and the CSV can start to work. With the 4.5 gallon size tank only holding about 1 gallon of water the drop from 60 to 40 happens fairly fast, the pump comes on, and the pressure hits 50 and stays there. With a 3 GPM shower this all happens in about 20 seconds and you are at 50 PSI. With a 0.5 GPM sink faucet the pressure will decrease for 2 minutes before the pump comes on.

A lawn pump or sprinkler pump does not build enough pressure to work with a pressure switch. You need a jet pump. A 1/2HP like a Goulds J5S would be best, but there are some really inexpensive versions of jet pumps as well. NT has a Drummond with tank and switch already mounted. Adding a CSV1A is not that tricky as many have done it. Don't think they last long but....

Thanks - ordering a valve right now. @valveman One follow-up where I would love your opinion - while the tank is depressurizing from 60 psi down to 40 I would think there is still a net water flow from the tank. Any chance the heater wouldn't be tricked during that time? I realize this is out of the scope of the valve but was wondering if you had an opinion. My tankless needs .4 gpm to activate and .26 gpm to stay running. I think the scala2 was faking out heater because it was slamming up against upper limit and shutting down really hard. I know you will not be able to tell me if flow past heater will be .2(no heat) or .3(heat) during depressurization but is it correct to say 'that the water in the tank is pressurized up the 60 psi and it wants to get out fast on its way to emptying the tank at which time the pump will turn on increasing the pressure and flow.' The reason I ask is I was thinking about a 2 gallon tank if I need to empty the pressure tank before water heater kicks in. My thought was toilet flushes and hand washing will deplete either tank and trigger pump. Bigger tank would save cycles only when someone gets a glass of water or use icemaker. Of course that thought could be totally wrong.

 

[Fitter30]

That lowes pump is not for domestic water its lawns and stock tanks. Just because it has a stainless housing it can have ferrous metals in it. As for as hot water flow your wh will limit it. Everyone of the condensing heaters have a max flow at a certain entering temperature. List all outlets for hw then how many will be used at one time and gpm.
Heres a calculator for mix water temp just change settings to gpm
https://www.spiraxsarco.com/resources-and-design-tools/calculators/water-mixing/water-mixing
After coming up with some gpms then a pump bladder expansion can be selected.

 

[Valveman]

Thanks - ordering a valve right now. @valveman One follow-up where I would love your opinion - while the tank is depressurizing from 60 psi down to 40 I would think there is still a net water flow from the tank. Any chance the heater wouldn't be tricked during that time? I realize this is out of the scope of the valve but was wondering if you had an opinion. My tankless needs .4 gpm to activate and .26 gpm to stay running. I think the scala2 was faking out heater because it was slamming up against upper limit and shutting down really hard. I know you will not be able to tell me if flow past heater will be .2(no heat) or .3(heat) during depressurization but is it correct to say 'that the water in the tank is pressurized up the 60 psi and it wants to get out fast on its way to emptying the tank at which time the pump will turn on increasing the pressure and flow.' The reason I ask is I was thinking about a 2 gallon tank if I need to empty the pressure tank before water heater kicks in. My thought was toilet flushes and hand washing will deplete either tank and trigger pump. Bigger tank would save cycles only when someone gets a glass of water or use icemaker. Of course that thought could be totally wrong.

Well I tried to explain that above? Whatever size bladder pressure tank you have, the pressure will drop from 60 to 40 as the tank empties. At 60 PSI your shower or faucet is putting our more water than at 40 PSI. So the flow decreases as the pressure decreases. Once the pressure drops to 40 the switch starts the pump, the tank quickly fills to 50 PSI. With the CSV set at 50 PSI, it instantly adjust the flow to match how much your shower or faucet will let out at 50 PSI constant. As long as the shower or faucet is open, the CSV will hold the pressure at 50 PSI steady, the flow through the shower will be steady, and the tankless heater will stay steadily on.

The smaller the tank the quicker this happens, but then the less draw down you have for small uses like the ice maker. A 2.2 gallon tank holds 0.5 gallons and a 4.5 gallon size tank holds 1 gallon. Any larger and you will be waiting for the pump to come on and the heater to get steady. But the 2.2 gallon really isn't large enough to get the run time needed or fill the ice maker. The 4.5 gallon size tank is a good compromise, but you may have to wait 30-60 seconds to get the water temp the way you want it for the sink, but not the shower.