Follwup: PEX & BB - in a retro fit

Carl

5 year old Two Story in Kings Park, NY with a forced air that was a builder bare bone special. Too costly to upgrade vs. a baseboard retro. In doing the retro to minimize wall/ceiling opennings, will 5/8 PEX work well for snaking purposes in the floor joist cavity and can I let it lay on the 1st floor ceiling as support? Looking at 5 zones for house plus 1 for indirect heater. Each room has been heat loss calced for BB. Currently 2 gas funances & water heater consume 240K BTU, looking at replacinig with a Burnham 205H 133K BTU Gas Boiler with Weil-McLain Gold Plus 60 Indirect Heater, & 6 Taco Pumps for zones.

kf_2

Pex

do not just lay the pex in the joist cavities. The expansion rates of pex are much greater than that of copper and the noise as it dances on your ceiling will keep you awake at night.

Also, carefully consult the pressure drop charts based on your lenghts of run and needed GPM's as pex has some extraordinary pressure drops and could require some very large pumps if not careful.


kf

Dan Peel

Check PAP

Do your numbers for tube sizing, 5/8 may well be enough flow. You will find the Pex-Al-Pex products much easier to direct over longer distances in enclosed spaces and only 10% of the expansion rate. Set up home run style and 1/2" tube will carry most BBd flow requirements. Dan

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heatboy

Absolutely!

To add to what Dan said, if you set a manifold and pull seperate S&R to each area, you'll be amazed when you can set the circulating pump to speed one (UP15-58) and use around 36 watts or so with a 10° Delta T across the baseboard and never worry about calculating temperature drop across the circuit. All with 1/2" tube. Wirsbo MultiCor in my case.

hb

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Carl

PEX & BB - Retrofit. Thank You & Check me on this please.

I just wanted to thank you gentlemen for your insight and direction. Just to make sure I am doing this correctly I have layed the system out with 5 heating zones, each having its own supply and return 5/8 inch pex lines. The zone demands have been calculated using Slant-fin’s heat loss Sheet 1502 methodology with results as follows using Slant-fin Model 30 BB rated at 580 btu/ft at 1 gpm, with boiler water at 180F:

Zone 1: 27ft BB = 15660 btu (den & kitchen)
Zone 2: 9 ft BB = 5220 btu (dining room)
Zone 3: 29ft BB = 16820 btu (foyer & living room)
Zone 4: 27ft BB = 15660 btu (2nd fl Master Bed,walk in closets & bath)
Zone 5: 25ft BB = 14500 btu (2nd fl 3 bed rooms and bath)

Total: 68,000 btu heating requirement.

To get my flow rate I divide each zone btu by 10,000. As a result no flow is greater than 2 gpm. The boiler will be in the basement and the longest zone run is estimated at 250 feet, for Zone 5, which yields (5/8 pex at a flow of 1.5 = 0.0245 loss/foot times 1.15) = 8.05 feet of head. Taco is widely available in NY so using their pump curve with the internal check valve (Model Taco 007 ZF5-IFC) the pump yields 10 feet of head at 2 gpm. So I chose to use this pump for each zone. I was not considering a reset for outdoor temp adjustments but it sounds like I sound add it to the design? I was just a bit concerned about having 5 pumps always running and the cost.

With respect to the Pex-A1-Pex recommendation, it sounds great. However, in order to remain married and not find myself sleeping on the couch, I need to minimize the openings in my finished walls for access. That is why I was looking to “snake” the pex up the walls and across the floor joists. The is an approach for the 2nd floor only as I have a basement where I can secure the 1st floor Pex supply and returns.

Again guys, any insight of suggestions are truly appreciated. I will be doing the work in stages, mostly due to money allocations, by running the Pex and installing the BB first, then installing the boiler and indirect hot water unit, and finally connecting the heating zones. Hopefully being ready for winter 2004.

Thank you again,

Carl

[Deleted User]

Per your figures

That size pex passes 1.5 GPM. Your figures are for 2 GPM. If you use 5/8", you may have greater than a 20° F difference on your supply and return.

You won't get 2 GPM, or 25% more than it can carry, through that pipe.

Noel

Rich_2

Retro fit

Have been using 3/4 pex for base board loops on the past couple of jobs, works great! Tight crawl spaces ,chop off a piece & go hole to hole with no fittings between the base boards any leaks will be on the board itself nice & exposed for easy repair