Recirculating pump advice

[dx]

I have a customer with a dead pump that my plumber will replace. Single circuit residential. The old pump was a a Bell NRF-22. I have 2 questions:

1. Was the Bell & Gossett NRF-22 an acceptable pump? I thought that is a hydronic pump and pretty high flow. Was it proper to use it as a hot water tank circulator?

2. My plumber likes the Laing UCT-303 as it has everything built in: check valve, adjustable thermostat, timer, air vent and even a ball valve shutoff. Is this a good pump? Are there any better pumps out there with all those features (or more) built in?

[Gary Swart]

I have been using a 303 Laing for several years with zero problems. It is a different model, there is no timer or adjustable thermostat and the check valve, air vent and shutoff are not built in. Mine operates 24/7. It would be possible to use a timer, but I like having the option of instant hot water at anytime. I'm sure there is an operating cost, but it is too small to notice on my power bill. The Laing is an excellent pump in my opinion. I have no information about other brands with everything built in, but there are a couple of other brands that seem to be quite popular as well.

[Redwood]

The B & G NRF-22 is a bad choice for DHW recirculation because it has a cast Iron casting.
In an open system there is oxygen present and the NRF-22 will corrode.
Brass and bronze castings and impellers are needed in this application.

Or, Is it the circulator pump on a zone for a Indirect water heater in which case it is okay.

[jadnashua]

I doubt an inspector would have approved that original pump for use on potable water...needs to be brass, bronze, or SS, which adds a lot to the cost of the thing.

[dx]

Yes, the pump is only for the water heater (potable water). No indirect heater on premises. That's what caught my attention. Client also has a clear bowl hot water sediment filter (stainless mesh element) after the water heater. Installed after complaints of sediment clogging hot water faucets. That filter now shows significant black and green deposits (according to client). I haven't looked at it but that tells me rust and crud from the pump and maybe copper pipe erosion. If I am interpreting the graph correctly, the NRF-22 is a much higher flow than advisable for recirc. And it ran continuously, no timer or thermostat.

[Redwood]

Sounds like you are on target with your assessment of the problems the system has.

[Thatguy]

If I am interpreting the graph correctly,

With help from Excel, I get
GPM = -1.47 x HD + 22
for the formula for the curve for this pump
http://www.bellgossett.com/productPages/NRFcurves.jpg
, so, for example, at a head of 4' you get 16.1 GPM. For a head of zero it's 22 GPM and for a head of 15' it's zero GPM.

[rickford66]

I'm not a plumber, but I have a recirc loop and I don't use a pump. My WH is in the basement, an so I let gravity do the job for me. It works great.

[Thatguy]

I'm not a plumber, but I have a recirc loop and I don't use a pump. My WH is in the basement, an so I let gravity do the job for me. It works great.

How much water do you have to run before it gets hot?
If it's 50' of half-inch pipe to the WH and you run a half gallon of cold water before it gets hot then there is no advantage.

Is this \/ how you did your system?

"
In my experience the gravity fed return loop is a better answer if you have the option to install insulation on the supply line(s) and an “extra” run of 3/4 inch pipe from the last hot water outlet back to the water heater.
To make the loop work, the 3/4 inch supply line must be insulated as it leaves the water heater and feeds each faucet that gets hot water. The return loop must also be insulated after it passes the last hot water tap in the house and returns to the heater. But the last 15 feet of the return pipe should have no insulation on it. By allowing the water in this portion of the pipe to cool, a very slow convection flow of water runs in the loop.
"

[rickford66]

That's almost exactly how I did it. The one exception is that I have a ball valve in the return line, next to the WH, that I have turned nearly all the way off. This ensures that, when hot water is turned on, that most of the water comes from the top of the tank, not the bottom. How long do I have to wait? I don't really. Almost every faucet on the run is within 2 or 3 feet of the loop. The loop stays hot, so I get hot water almost immediately. The longest takes about 3 to 4 seconds because it is the furthest from the loop. For example, the half bathroom, at the opposite end of my house from the WH, gets hot water in about 1 second. Compared to the 60-70 seconds I had to wait before, it's wonderful. My wife loves it too.

[ballvalve]

I want to know where you plumbers decided that any cast iron fitting is forbidden in a plumbing system? The jet pump that feeds the house is likely all cast iron, including the impeller. The mains in the street are probably ductile iron. How about those billions of radiators out east from the old days?

Wet sprinkler systems still use ductile iron pipe which is about as close as you can get to cast iron on the scale of elements. What IS garbage is "galvanized" pipe, within each fitting about 20% of the surface area is raw steel exposed to the water. Instant rust and onward to a leak from moment of installation.

Cast iron develops a resistant oxidized surface, and no longer "rusts" - why doesn't anyone understand this when CAST IRON lasts forever in acidic DVW systems that makes water look like oil to a pipe.

I have always used grundfos cast head pumps in open or closed radiant and never had rust or a failure.

What about all the boilers that use cast iron heat exhangers? Whats with the fear of a 10 square inch area of cast iron impeller head in a circulating pump?

[jadnashua]

A closed system works fine with cast iron since you are not adding fresh water constantly, all of the oxygen gets used up and the water is realtively inert. This is not so in potable water...constant supply of oxygen is mixed in the water, so you get the opportunity to continually rust the stuff.