Are there any special requirements

Chris_4

a Rinnai tankless heater to a hydronic system??

this will be my first.

I hear the flow is critical!?

the unit will be serving an 1800' slab on grade shop.
heat loss for the building is 52000. the contractor ran 3/4 tubing in the slab, 12" centers and can't be changed as slab is already poured.

can it be directly connected, or should a buffer tank be installed?

any advice is appreciated

Thanks

Chris

Al Letellier

Rinnai heater

I assume you're talking about a Continuum heater, right. Have several installed and the load will dictate the need for a buffer tank. I assume you know the head loss is very high through these units. (Taco 009 minimum)the variable firing rate is great for low load situations but the unit will short cycle if the load is too small and a buffer or indirect may be in order. Call the folks at Rinnai, they've been great with the tech support.

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Alan(CaliforniaRadiant)Forbes

Rinnai

Previous thread on Rinnai for radiant:

Date: July 31, 2003 04:07 PM
Author: Rob Garcha (kgarcha@cox.net)
Subject: Rinnai water heater

Allan, How are you handling the high pressure drop across the heat exchanger. My understanding (limited as that may be) is that the unit has a built in modulating valve that restricts flow in order to instantly heat the water. I would be interested to know what your piping strategy / pumping strategy is. Rob


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Date: July 31, 2003 05:31 PM
Author: Alan(CaliforniaRadiant)Forbes (adforbes@pacbell.net)
Subject: Rinnai

has a brochure called "Standard Circulator Applications" and in it is a chapter called "Hydronic Heating Pump Selection" where they recommend primary/secondary piping with the primary pump capable of 6 gpm/30' head; that's a Taco 0013 (whew!).

They go on to say that the formula for determining BTU output is GPM x Delta T x 500 = BTU. In the past, Rinnai reps. have come on The Wall to say that 6 gpm is the max. you can get out of the Rinnai for space heating, but theoretically you should be able to size the pump up to the maximum output of the water heater. So, since the Rinnai has an input of 199 KBTU, it's output (if 80% efficient) is about 160 KBTU. If you could find out the performance data and size the pump to flow 16 gpm (at 20° Delta T) at whatever head, you should be able to utilize the full output of the little devil.

But no, they don't seem to want you to go over 6 gpm and perhaps it's because it's just too much pressure on the water heater itself.

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Chris_4

thanks

thanks guys, I have contacted Rinnai, and hopefully will get all the details. just thought some of the real world experiences might come in handy also.

thanks again

Chris

Paul Rohrs

Watch...

The minimum psi ratings. I believe they want to see 40psi through the heat exchanger. Recharge the expansion tank since it is only factory charged at 12psi. This will also affect the relief valve setting so watch for that as well. I have a few units under my belt and seem to be working fine.

Regards,

PR