Recirc pumps for Rinnai RU199k?

rbphhc

Hi all,
Rinnai recommends the GTK03 pump kit for DHW recirculation in their tankless units, which is a stainless Grundfos Alpha 15-55 pump @ 20 GPM and 17 ft of head.
I'm wondering what other pumps out there have similar specs?
Needs to be bronze/ SS/ composite, of course, with enough oomph to push through that tankless.
Taco 006-ST4 at only 10 GPM @ 9 ft of head presumably won't cut it. The 007 is 23 GPM but still only 11 ft of head. 008 starts to get up in the ballpark @ 15GPM/15ft head.
What about composite ECM? Looking for any alternatives.
Thanks!

hot_rod

Here is a pump curve for that 15-55 flow and head are related. As pressure drop goes up gpm goes down. Use the pressure drop from the other post, for your specific heater.

That circ may be enough for flow for the loop heatloss. It would not be enough if you are trying to recover the tank quickly, a buffer, as the boiler will not ramp up under low flows.

There is no cheap answer for non ferrous circs.

rbphhc

hot_rod said:

Here is a pump curve for that 15-55 flow and head are related. As pressure drop goes up gpm goes down. Use the pressure drop from the other post, for your specific heater.

That circ may be enough for flow for the loop heatloss. It would not be enough if you are trying to recover the tank quickly, a buffer, as the boiler will not ramp up under low flows.

There is no cheap answer for non ferrous circs.

Understood. I just spoke to Rinnai, they said that in my application (recirc to buffer tank, with very little actual head)(in VT w/ 80°f delta, so slow anyway), undersizing the pump might be OK.

Of course recovery rate will be reduced, but it will get there eventually. Tech said a 006-ST4 should do it (10ft, 10gpm). Second opinion?

hot_rod

006 at 10' looks like 0 gpm to me, maybe they have Rinnai specific pump curves

5 gpm at 5' is the mid curve, a good spot to run.

A 008 would be my thought.

rbphhc

hot_rod said:

006 at 10' looks like 0 gpm to me, maybe they have Rinnai specific pump curves

5 gpm at 5' is the mid curve, a good spot to run.

A 008 would be my thought.

Funny, that's exactly what I have in the check-out basket!

rbphhc

hot_rod said:

A 008 would be my thought.

Found a good price on a 00R-SF6-IFC (save a couple hundred bucks), which is stainless and fits the flow curve nicely. On low speed, basically equivalent to the 008 or the recommended Grundfos 15-55 (7gpm @ 7ft), and has the option to step up to 9@8 or actual 10@10.
Any reason I shouldn't use a pump designed for radiant in a potable HW recirc application?

rbphhc

hot_rod said:

A 008 would be my thought.

Am I crazy, or does a 006e3 do everything we need? It's composite, 3-speed, develops 10ft of head at 6gpm on 'Max,' cheap-ish, with possible rebates...

(Of course, the 0015e would be working way less hard, and there's a nice stainless/ union model, but again twice the money.)