On demand Pump

boomadge · February 2015

I currently use a 12V DC on demand Flo Jet that puts out 2.9 Gpm at 40 psi for my cabin. The problem lies with my on demand hot water heater that requires 2.1 gpm flo to operate properly. So sometimes the heater will kick off.
So I am looking into getting a better on demand pump. I have 24 volt solar setup with 1500 watt psw inverter so I have a choice of 12V/24V DC or 110V AC type. These are the three I am looking into, just not totally sure what
one is my best choice. Any input would help..

make model switch gpm/lpm psi/bar max draw valves/diaphram ports volts connection

seaflo SFDP1-050-060-51 Demand 5.0/18.9 60/4.1 17.0A EPDM/Santoprene 1/2"-14 MNPT 12V DC 2-Pin/Leads

seaflo SFDP2-050-060-51 Demand 5.0/18.9 60/4.1 9.0A EPDM/Santoprene 1/2"-14 MNPT 24V DC 2-Pin/Leads

seaflo SFDPA1-045-040-41 Demand 4.5/17 40/2.8 1.0A EPDM/Santoprene Quick connect 110V AC US grounded

Mountain Don · February 2015

If the battery bank is 24 volt, I'd go for the 24 volt version myself.

OR, better yet I think, I'd find a water heater that would work with a reduced flow rate and also save water. There are on demand heaters that will start on less than 0.6 GPM and continue to heat water with a flow through the water heater as low as 0.26 GPM. (Rinnai) What's the flow rate of the shower head or sink faucets you have? The fed standard is a maximum of 2.5 GPM and ours are all less than that. Also that is full flow, hot and cold mixed, so the flow through the water heater should be less than the flow out the faucet/shower. No wonder then that your heater will shut off at times when cold is being mixed with the hot. That results in less than the minimum flow through the heater. I am not sure a higher capacity pump will solve the problem.

boomadge · February 2015

Its the shower that only gives me issues, so i changed the shower head to a 1.6 gpm and it helped but when you combine cold and hot together it likes to trip the tank. I have made adjustments with tank flo and can resolve the issue most times, but its a pain to keep adjusting. Was thinking a bit stronger pump might be better.

vtmaps · February 2015

I agree with Don... get a better water heater. I think your problem is not the pump... If your showerhead only allows 1.6 gpm, and your water heater needs 2.1 gpm, the system wn't work no matter how large the pump is.

Also be sure to avoid the 120 volt AC demand pumps... they work on high voltage DC which will ruin the negative brush.
http://forum.solar-electric.com/forum/solar-electric-power-wind-power-balance-of-system/solar-water-pumping/21544

--vtMaps

jonr · February 2015

Get a bucket and measure the flow rate. You will need approximately the rated 2.9 gpm of total flow to satisfy the water heater's need for 2.1 gpm of hot water flow (maybe more, it varies with the temp of the incoming water). The wrong head and/or small pipes might be too restrictive and something like a 60 psi 4+ gpm pump would help. A higher flow head would be cheaper.

I know people who just crack open the sink hot water faucet while they shower. Wasteful, but it works.

hemmjo · February 2015

Why not install a pressure tank to provide the short term flow you need save the on/off cycles of the pump?

How do you power the demand water heater?

Just curious.

boomadge · February 2015

It is propane with electronic ignition, and works perfect If I use hot/cold at kitchen sink. When using the shower open hot valve tank kicks on fine, then slowly open cold to get temp of water good. jump in shower and randomly without warning I can hear the on demand heater shut down and then the water is naturally cold. Shut off cold/hot valves repeat process..

706jim · May 2015

jonr wrote: »

I know people who just crack open the sink hot water faucet while they shower. Wasteful, but it works.

That is hilarious! Those on demand heaters are supposed to save money and from what I have seen, they are more trouble than they are worth.
Very fussy about quality of water going into them (silt and minerals) fussy about pressure and flow and more expensive to purchase initially.
My 5 gallon (oops 6 gallon....) RV heater is starting its 32nd season and is fed with lake water containing a fair amount of silt and still works fine.
I think there is something to be said for the traditional water heater that has been a staple for so many years.
One thing never mentioned is the fact that any waste heat radiated from the tank will tend to heat the structure that contains it.
Not great everywhere, but actually a benefit in Canada where the furnace runs most of 8 months oer year.

Dave Angelini · May 2015

706jim wrote: »

That is hilarious! Those on demand heaters are supposed to save money and from what I have seen, they are more trouble than they are worth.
Very fussy about quality of water going into them (silt and minerals) fussy about pressure and flow and more expensive to purchase initially.
My 5 gallon (oops 6 gallon....) RV heater is starting its 32nd season and is fed with lake water containing a fair amount of silt and still works fine.
I think there is something to be said for the traditional water heater that has been a staple for so many years.
One thing never mentioned is the fact that any waste heat radiated from the tank will tend to heat the structure that contains it.
Not great everywhere, but actually a benefit in Canada where the furnace runs most of 8 months oer year.

not to mention that you need a tank to heat water with the sun, the old fashioned way.....

petertearai · May 2015

What about a booster pump . Turn on when having a shower.

boomadge · May 2015

I replaced the the flowjet with a seaflo 5.5 gpm and problem solved. Woot no more hot water issues..old pump might of been tired.

Deveak · January 2016

whats the pressure like on the seaflo? I m looking for a good pump but i cant seem to find any that can handle decent pressure or flow. Its one or the other. They advertise 45 psi but its at 1 gpm or so. I want 2 gallons per minute at 45 psi.

ramloui · January 2016

Late to this conversation but...

I had the exact same issue with my propane water heater. My fix was to change the 1 handle faucet for the 2 handle faucet: open the hot side fully and then adjust temp with the cold side.

The only downside side now is that when I cycle the the hot water on and off (as when I'm shaving) the darn water heater does not fire fast enough before I turn the water off. The work around for that was to leave the hot water running for the task duration. Wasteful...

If that water heater dies, I will go to a basic water heater with tank...

Louis R.

zoneblue · January 2016

A quick fix for this might be to just add another identical flojet in parallel. Those pumps run quite well in parallel. But agree with the others the problem is the califont. The (cheap) unbranded one we use runs fine off a shurflo 2088.

just starting · January 2016

I have a 4.3 gpm marey flowthro water heater and a 5gpm 60 psi seaflow pump with a 20 gal pressure tank my water tank sometimes freezes and with ice chunks in tank. water still gets to 125°f and I'm at 10k above sea level been in place for 17 months works great

just starting · January 2016

Had to bypass pressure switch in pump and put in a real pressure switch

On demand Pump

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