Print

[Chas]

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.   

[slimjim]

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.

[Scott7m]

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...

[slimjim]

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

[ST98]

When putting a pump on the boiler where its not pressurized is a cast or a bronze pump used?

[Chas]

Cast is fine. Bronze pumps are used more with potable (domestic) water. But either will work.

[slimjim]

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.

[ST98]

Thanks. I wasn't sure open versus closed.

[yengbryan550]

thanks for some tips above