Outdoor Wood Furnace Info
All-Purpose OWF Discussions => Plumbing => Topic started by: automan77 on September 10, 2013, 05:36:42 PM
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I have a Bell & Gossett nrf 36 and want to buy a backup pump that would be comparable with the 36. I really don't want to spend 300 bucks. would the Taco brand have a pump that would be comparable with the bell & Gossett 36 that would fit my hookup. I run 1 inch pex.
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Hey Scott
I have the Bell and Gosset nrf-25 3 speed pushing 180 ft from my basement back to the boiler through a sidearm, a HX, and a whole bunch of 1" copper 90's. According to my spinning flow indicator it's working great. I got them on E bay for $90 each with free shipping. 1 for the house, 1 for the shop and a spare on the shelf.
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just guessing but i think these pump makers will be in a very close cost range for pumps that are of comparable gpm and head range?
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The NRF36 is a pretty good sized pump. Not really anything cheaper unless you go chinese.
If you just want to stay with the same pump, I may be able to get you a good deal on one. Will be way less than $300.
If you go to a Taco, the 0011 is close or the 2400-wb. Both are single speed though and yours is 3 speed.
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Hey Scott
I have the Bell and Gosset nrf-25 3 speed pushing 180 ft from my basement back to the boiler through a sidearm, a HX, and a whole bunch of 1" copper 90's. According to my spinning flow indicator it's working great. I got them on E bay for $90 each with free shipping. 1 for the house, 1 for the shop and a spare on the shelf.
What kind of return temperature do you get when there is heat load? That pump sounds slightly small with that much on the system. If you had a plate heat exchanger instead of the sidearm it most likely wouldn't work too good since there would be larger demand when DHW is running.
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Yep, could be another common case of "we'll my home is warm so i know my pump is big enough".
That's def not a good way to tell
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Temperture gauges on supply and return can tell a guy a lot.
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I have one on my supply line
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Just grabbing the pipe can tell a lot too. If it just feels warm and the supply is hot then you probably have an undersized pump. 150° is usually about as cold as you want it to go and that temp you can probably keep your hand on the pex for at least a few seconds.
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Temp gauges are relativly cheap and they can tell a lot
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Ok RSI, I can now answer your question. I just did some checking and my inlet temp coming into the house was 177º, after going thru the sidearm and the furnace HX with the furnace blower on, my temp had dropped 30º to 147º. Is this exceptable or this an indication that my pump is to small? I'm a newbie so I don't know what the optomum temp drop across the HX is. With the furnace blower off, I have about a 2º drop from inlet to outlet, 177º to 175º.
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147 is ok but when the supply water temp drops it might go a little too low.
You might want to consider adding another pump in series and connect it to come on with the furnace blower.
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temperture differential from supply to return on the wood boiler as a general rule should never be more than 20 degrees, more than 20 degrees will shock the boiler when it returns, this is thought to be one of the major problems with rot out by many of the manufacturers, do as you wish but I personally would be either upsizing the circ or putting a second circ in line to reduce resistance and get the flow up, don't put them close together or they will cavitate and destroy the circ.
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Some pump manufacturers say you can bolt two pumps right together. Have you ever seen one cavitate from being to close to another?
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Yes you can bolt them directly together, most companies I've talked to actually warned against separating them, said there was more risk in doing it like that vs the in series method. We've done a lot of pumps bolted together and not had an issue.
Slim, could you explain this "shock" to me?! Now I fully understand the science of keeping return water temps safe, but could you explain the actual science that could lead to boiler degradation if let's day your set point was 190 and it returned at 155? Well over 20 degrees.
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Well, I've read enough on this site to convince myself that my NRF-25 isn't moving the water fast enough. I just ordered an NRF-36. My OWB is 180' from the house, pump in the basement, but my entire system in the house is 1" copper, no pex at all, which means lots of 90's and 45's. It cost a little more but boy does it look sweet!!! I was losing 30 degrees across my 20"x 20" HX and from what I'm reading, that's too much. As Scott7m stated earlier, "another common case of, well my home is warm so I know my pump is big enough". Guilty as charged Scott.
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Boiler return temps returning more than 20 degrees cooler than supply line will create a cold spot in the boiler that can eventually warp or erode the steel, at the least the temps can drop enough to create more condesation in the boiler creating more creosote mixing with condesation, the hotter the boiler is run the less condensation and creosote happens, why would anyone wish to do this to thier investment. I have seen cast boilers actually crack from cold water returns, speak with the good oil boiler manufacturers and they will tell you that the return temps should always be protected, this is why most wood boiler manufacturers are insisting on an in line mixing valve between the supply and return.
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Boiler return temps returning more than 20 degrees cooler than supply line will create a cold spot in the boiler that can eventually warp or erode the steel, at the least the temps can drop enough to create more condesation in the boiler creating more creosote mixing with condesation, the hotter the boiler is run the less condensation and creosote happens, why would anyone wish to do this to thier investment. I have seen cast boilers actually crack from cold water returns, speak with the good oil boiler manufacturers and they will tell you that the return temps should always be protected, this is why most wood boiler manufacturers are insisting on an in line mixing valve between the supply and return.
Yes slim, but the goofy part is, that the mixing valve actually makes the problem worse. If the system was sized properly to begin with and everything calculated out properly there would be no need for it, but as manufacturers they can't control what every dealer they have knows or that customers won't add things even if everything were perfect. What I mean by making it worse is that as soon as the hot water leaves the boiler it gets robbed to some degree, I don't like that, it's like putting a patch on a hole instead of fixing the darn hole. But we do what we gotta do
I have never seen any evidence though that you'd have issues as long as the returns were above the 140 range. At least in outdoor wood boilers, one case of the p and m failure we all saw go down on here was one I talked with them about in Louisville, they said his return temps were around 100 degrees. That's enough to make it sweat like a pig...
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I agree and do not like the mixing valve on the wood boiler but that is the way the manufacturer makes sure the return temp is protected when installed by the homeowner, as for those of us that install professionally and do monitor those temps I believe there is no need for the mixing valve
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When putting a pump on the boiler where its not pressurized is a cast or a bronze pump used?
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Cast is fine. Bronze pumps are used more with potable (domestic) water. But either will work.
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Cast is all I use as bronze circs are lots more money and don't seem to last any longer, what kills the circ is either cavitation or foriegn particles in the water that siezes the circ. Are you guys are aware that the circ can be taken apart at the motor housing and you can free up a stuck circ by simply turning by hand the nylon impeller, you won't even have to take the wires out just be sure to kill the power.
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Thanks. I wasn't sure open versus closed.
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thanks for some tips above :)