I asked a question about flow velocity on Woodsmaster's post about PEX insulation. It was taking that topic pretty far afield so I thot it better to start a new post. It's no secret I've designed my system basically from inputs at this web site. I'm pleased with all my above ground decisions. Because I now have the data that indicates my PEX is immersed in water at some point in the transit from my barn to the cellar I'm going to dig up my lines and polyurethane my 1 1/4" PEX probably in the next few weeks. Winter's about over for us here. Because in all my previous research last Fall I never heard of anyone needing 1 1/2" PEX and all the debate was focused on 1 vs 1 1/4. I thot my decision to go 1 1/4 and not consider 1 1/2" was adequate. Now that I'm going to dig up my lines for the LAST TIME of my life we're gonna do it right. The following is my assumptions and a question about when does the flow velocity get excessive. If I need to add a 1" line to my 1 1/4" to reduce the flow velocity, now's the time. Thanks in advance as usual. I don't remember maximum flow velocity (feet/sec) ever discussed here before, its always focused on flow rate (gpm). The following was asked of Heaterman in the insulation post but any input is appreciated:
Heaterman, Your reply made me feel somewhat better about my 1 1/4” piping system. Per the Taco TD10 data sheet I knew I’d be exceeding the TD10 maximum 1 1/4” recommended flow rate of 11.2 gpm. With my computed head loss of a little more than 22 feet and assuming my 210kbtu boiler could consistently put out about 170kbtu I computed a required flow rate of 17 gpm (20F deltaT). Those two numbers flow rate and head put me right on the Taco 0013 curve. I had not read of anyone here using more than 1 1/4” PEX so I presumed others were routinely exceeding the recommended flow rate on 1 1/4” PEX. The existing 115kbtu propane furnace was adequate to keep our downstairs adequately warm during our short heating season, so I didn’t attempt to do a heat loss. Since I’m about to dig up my PEX to foam insulate, from your experience am I way over pushing the flow rate in that 1 1/4”? Until recently I don’t recall ever hearing discussions about 1 1/2” PEX.
The TD10 document implies the gpm limits are to keep flow noise at acceptable limits. But they also say keep flow velocity between 2-4 fps. At 17 gpm and 1 1/4” I’m at 6.25 fps! Now I’m wondering if I need to add a 1” line to my existing 1 1/4”. Geez what a learning experience related to the underground part of this system.
Heaterman, Your reply made me feel somewhat better about my 1 1/4” piping system. Per the Taco TD10 data sheet I knew I’d be exceeding the TD10 maximum 1 1/4” recommended flow rate of 11.2 gpm. With my computed head loss of a little more than 22 feet and assuming my 210kbtu boiler could consistently put out about 170kbtu I computed a required flow rate of 17 gpm (20F deltaT). Those two numbers flow rate and head put me right on the Taco 0013 curve. I had not read of anyone here using more than 1 1/4” PEX so I presumed others were routinely exceeding the recommended flow rate on 1 1/4” PEX. The existing 115kbtu propane furnace was adequate to keep our downstairs adequately warm during our short heating season, so I didn’t attempt to do a heat loss. Since I’m about to dig up my PEX to foam insulate, from your experience am I way over pushing the flow rate in that 1 1/4”? Until recently I don’t recall ever hearing discussions about 1 1/2” PEX.
The TD10 document implies the gpm limits are to keep flow noise at acceptable limits. But they also say keep flow velocity between 2-4 fps. At 17 gpm and 1 1/4” I’m at 6.25 fps! Now I’m wondering if I need to add a 1” line to my existing 1 1/4”. Geez what a learning experience related to the underground part of this system.