Replacing old boiler, have a piping question

[neoncrazy101]

Hello, I am replacing our 37 year old boiler with a new Rinnai wall mounted unit (non combi). I was doing an inventory of what I could use from my old system with the new system and ran into an issue. On the old boiler it was a simple In and Out on the water piping with it being daisy chained throughout the baseboards/radiators (so no separate zoning per room) using a single circulating pump. I was reading in the manual for the Rinnai that it REQUIRES the use of a primary secondary heating kit or a low loss header. Do I really need that if its a single zone though? When I've searched online I keep running in to people having them installed with multiple zones but I couldn't find one with someone using it on a simple single zone.

 

[PoorUB]

Yes, you need to use primary/secondary plumbing on most high efficiency boilers. These days I would probably plumb a cast iron boiler that way. It insures the boiler has the water flow rate it needs to function properly.

Don't second guess it, just do it. I have seen too many installers try to cheat and have nothing but trouble with the boiler afterwards.

 

[Sumboodie]

Sounds like the old boiler was done wrong. Primary/secondary is SOP. Keeps the boiler temp steady and no thermal shock.

 

[Jackfre]

Taht boiler is set up to deliver a specific supply temp to the LLH/Secondary loop. It will modulate the primary circ before modulating the burner. The real reason for pri/sec is to remove the pressure drop from the boiler from the secondary side. It makes it a lot easier on the secondary sides circ and just smooths everything out. You want that. I installed a Rinnai M series for a friend on a small radiant job without P/S. Shortly after Rinnai came out banning that configuration so I went back and repaired it. The I models all require P/S. We moved 6 mos ago and I threw out a lot of Rinnai parts including 4 LLHs. Bad timing

 

[fitter30]

Since the new boiler doesn't hold much water like your old cast boiler it needs constant flow through it so that coil won't over heat from low flow. Old boiler was piped with 1 1/4" pipe or larger new boiler 3/4". Might also look at Taco E series pumps they use a ecm motor which is more efficient. Spirovent for air elimination and Rectorseal 8 way boiler treatment.

 

[neoncrazy101]

Yeah the old boilers piping is 1-1/4".

Do I need to add a second circulator pump to it? One for the primary and one for the secondary? I was going to be buying a new Grundfos UPS 15-58.

 

[danski0224]

Boiler instructions should tell you what pump to buy.

Follow the near boiler piping instructions in the installation instructions, not random people on this forum.

 

[neoncrazy101]

Boiler instructions should tell you what pump to buy.

Follow the near boiler piping instructions in the installation instructions, not random people on this forum.

Instructions list the 15-58 as one of the recommended but only lists pumps for the primary but I've seen diagrams showing a pump on the secondary as well but not sure if that's only for multiple zones or what not.

 

[danski0224]

You need a secondary pump (circulator).

One pump circulates through the boiler, primary loop. The manufacturer knows what pump is needed there.

You then need a pump (circulator) for each zone. If the whole house is one zone, then you need one more pump.

They do not specify what pump is needed for the secondary loop(s) because the manufacturer doesn't know the design of your system. You or the heating contractor needs to figure it out.

A hydraulic separator makes primary/secondary piping easier. Caleffi has one that also includes an air separator, a magnet, a dirt trap and a hose connection to drain off the dirt. Not cheap, but it saves on the number of separate items, labor and fittings.

I've heard that "high efficiency" boilers do not do well with high mass (cast iron) and high water volume systems. Efficiency is lost as water temperature goes up. BTU output of the radiation is determined by water temperature.

Debris in old radiators is not good for Itty bitty high efficiency boiler heat exchangers. A dirt trap is a must.

 

[Jackfre]

The primary pump is built into the boiler

 

[Mike007]

A dirt trap is a must.

Absolutely. There's magnetic strainers available now reasonably priced. I've seen multiple condensing boilers ruined when the heat exchanger gets blocked with metal debris from the old radiators and/or boiler.

 

[danski0224]

The primary pump is built into the boiler

Nope.

Not on I series.

Instruction manual CLEARLY calls out boiler loop circulator suggestions on page 56. First line on the page states that a boiler pump is not included.

Diagrams CLEARLY show second system loop circulator on page 53.

OP needs to read the instructions.

 

[Jackfre]

I just looked at the Rinnai site. The ”integrated” circ is shown In the lower rt of the case on the I model.

 

[American Locomotive]

I just looked at the Rinnai site. The ”integrated” circ is shown In the lower rt of the case on the I model.

Rinnai Combi boilers have an integrated circulator pump, the standalone "heat only" models (which OP has) do not.

Combi boilers do not pipe the domestic hot water directly through the main firing heat exchanger. They instead use a separate water-to-water flat plate heat exchanger that transfers heat from the primary loop into the DHW circuit. So they need an internal circulator otherwise the DHW function could never work.

 

[Jackfre]

Shucks! As I go down in flames, thanks for correcting me

 

[fitter30]

Just use your old pump for the secondary loop. Primary loop is going through the boiler.