1 1/4" versus 2x 3/4" pex pipes from boiler shed

[Splitz]

I am installing an EKO 40 in a boiler shed aprox 140 feet from the house and need to run pex lines to the existing heating system. I am installing them in a foamed in place trench frames by 2" foam insulation. I have been absorbing vast amounts of info on this site from all of the people here who either know what they are talking about or have learned from trial and error. To both of these groups I owe a dept of gratitude for saving me alot of time, money and frustration. I was planning on using 1 1/4 inch pex (w/ oxygen barrier) underground and was about order to a three hundred foot roll from PexSupply and noticed that 3/4 inch is substantially cheaper. Is it alright to use two runs of 3/4" instead of 1 run of 1 1/4? To my mind it works out to more capacity and would be about the same once you factor in fittings and restriction. (not that i've done the math!)
Am I wrong or would this work? Even when you add the extra fittings and parts it is alot cheaper.
Thanks for any thoughts

By the way I almost puked when I figured out the cost for copper to plumb my system so decided to use 1" pex instead for my secondary loop (primary is 1 1/4 copper) I looked at alot of systems and never saw one like this so hopefully it works. If any one has done this let me know. Also any criticism is appreciated, I would rather know now before it gets cold.

"Thats alot of space to heat!"

 

[ewdudley]

I was planning on using 1 1/4 inch pex (w/ oxygen barrier) underground and was about order to a three hundred foot roll from PexSupply and noticed that 3/4 inch is substantially cheaper. Is it alright to use two runs of 3/4" instead of 1 run of 1 1/4? To my mind it works out to more capacity and would be about the same once you factor in fittings and restriction. (not that i've done the math!)

Check these out when you're ready to do the arithmetic.

http://www.viega.net/cps/rde/xbcr/en-us/Viega_PureFlow_ViegaPEX_Ultra_Tubing.pdf

http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf

btu_per_hour = gpm * 500 * deltaT_degF

And nice job on the pex, the stuff is so ill-behaved it's hard to have it come out looking as sharp as that!

Cheers --ewd

 

[brad068]

Is the hot side the top horz. line? Is this like a secondary primary and a secondary secondary? Don't know if that is the correct terminology.

 

[heaterman]

A pair of 1" maybe but not a pair of 3/4".

A single 1-1/4 has almost twice the annular area as a pair of 3/4 tubes.

 

[Splitz]

Getting the pex straight was a pain but i wanted a clean look. I discovered that if i unrolled it and left it on the heated floor for a couple of hours it was a little more forgiving and stayed slightly more straight...slightly
The hot is the top horizontal line, flow is from right to left. It is a primary secondary setup...not sure about secondary, secondary...i'm not a heating guy just a DIY so I don't know the terminology either. I just read a sticky that gave flow rates for different size of pipes and see that 3/4 is not going to deliver the same amount of flow as 1 1/4 pex. Should have read that first i guess, lots of good info here, hard to get to it all in time

 

[ewdudley]

A pair of 1" maybe but not a pair of 3/4".

A single 1-1/4 has almost twice the annular area as a pair of 3/4 tubes.

Hmm. The charts show a single 1.25" pex as having 2.47 times the cross sectional area of a single 0.75" pex.

At any given pressure drop, a single 1.25" pex will flow over three times the rate of a single 0.75" pex.

--ewd

 

[Tennman]

How much is "a lot cheaper"???? You will never hear anyone at this site say, "Boy I wish I went smaller on my underground..." I went "cheaper" on my FIRST install.... Oh, yeah.... cost me $2000 to REDO it right. I'm sorry. I'm the Poster Child for the Coalition Against Screwed Up Undergrounds.

 

[salecker]

Hi
I was going to run 1 1/4" lines when i did my lines.My supplier wasn't able to get it in time so he suggested two 1" lines.I used Rehue line and really liked their fittings.Apparently Rehue has certified unions for underground splicing.I had to splice the lines about 20 ft from house underground.I pressure tested before the insulation and backfill.The way i was told to tie them together left me wondering about restricion,but time will tell,i will be heating the whole house this winter,just with a big temporary heat exchanger.Next year i will have all the cast iron rads in place so i have to wait to see if everything will work together.
My run is about 120 ft,so far i have not been able to read a temp drop on my lines when there is no load in the house,but all i have is an IR gun to measure temps.
Thomas

 

[Splitz]

Tennman: Good point by you!
Wasn't trying to go "cheap" just trying to figure out how to get this installed and feed kids as well...this type of system is efficient and long term benefits are obvious but the initial outlay is costly...looking for another way to skin this cat...hmm...i wonder if the kids would eat the cat (just kidding!)

 

[Hunderliggur]

1 1/4, sorry. You will be happier in the long run. Of course I figure you (or someone) calculated the required heat load transfer and came up with the 1 1/4". I have a Paxo 40 and use 160' of 1 1/4 (80' PEX underground, 80' copper in basement). No problems. My heating system is copper, but the underfloor is PEX as well as all the domestic supply lines.

 

[Frozen Canuck]

I would second what Tennman said, this (underground) is probably the #1 area where you can hurt yourself really bad on a DIY install. He shared it all for us to learn from in the stickie at the top of the page. If you have not (yet) those stickies are full of really good info, save us all a lot of money by learning from others. Unless I misunderstand your post (very possible) I would use more than two inches of spray foam esp. in our climate. Was wondering if you had a large price diff. on the O2 barrier pipe vs the PAP pex/aluminum/pex. PAP pipe will be a 100% O2 barrier, coated pipe only until someone scrapes the outside coating. Just curious whether PAP pipe was a pile more in the East. BTW is that an old dollar bill in the photo? Have not seen one of those in years. Best of luck with the project.

 

[in hot water]

something doesn't look right in your piping. I don't see a circuit for the boiler pump to work. It seems the only path from the boiler and back is thru that 3 way valve at the left side of the piping? Usually the 3 way valves are piped off a primary loop with closely spaced tees so the boiler pump has a complete circuit, or loop that can supply hot supply to every H port on the 3 way and the return temperature blends back into that valve at the C port.

Here is a link to an article with some drawings that might clear that up. Maybe I'm not seeing all of the piping correctly.

www.pmmag.com/Articles/Column/8da575554ffc7010VgnVCM100000f932a8c0____

If you have an i-phone or smart phone download the Photosynth app. it allows you to take panorama pictures and it connects all the frames together. Pretty slick! I'm not sure if you could post the final picture here however.

hr

 

[brad068]

something doesn't look right in your piping. I don't see a circuit for the boiler pump to work. It seems the only path from the boiler and back is thru that 3 way valve at the left side of the piping? Usually the 3 way valves are piped off a primary loop with closely spaced tees so the boiler pump has a complete circuit, or loop that can supply hot supply to every H port on the 3 way and the return temperature blends back into that valve at the C port.

Here is a link to an article with some drawings that might clear that up. Maybe I'm not seeing all of the piping correctly.

www.pmmag.com/Articles/Column/8da575554ffc7010VgnVCM100000f932a8c0____

If you have an i-phone or smart phone download the Photosynth app. it allows you to take panorama pictures and it connects all the frames together. Pretty slick! I'm not sure if you could post the final picture here however.

hr

This is what I'm seeing too. I think the third pic is where the primary loop is at. I questioned that it looks like one big secondary ( primary) loop with the in-floors being the secondary (secondary) loop.

I just wonder how well that will work when all sec, sec. loops call for heat.

 

[rkusek]

Please describe your heating method on the zones. I'm guessing it must be stape up or in floor radiant since you have the mixing valves. I may be totally off base but I would think 1 loop with closely spaced tees off the primary loop, with just 1 circ, with just 1 mixing valve, but with a 4 tap manifold for each radiant loop would be a better solution. These 4 taps could have zone valves if they are separate rooms on separate thermostats or if all the same room the thermostat could just cycle that 1 circ. Maybe these are not radiant loops and I'm totally off. Post a diagram of your plumbing and I'm sure the experts here can help you make sure it's going to work. If you're doing primary secondary the main benefit of it would be to connect such items like your wood boiler, existing oil/gas boiler(for backup), storage tanks(optional), and the items drawing heat (ie. DHW, radiant heat, air handler HX, hot tub HX, pool HX, garage or shed heater) with the closely spaced tees. The reason is the primary loop doesn't care whether these items are adding heat or extracting heat from the primary loop and it eliminates the problem of trying to balance things when the heat output and heat demand varies. I think it would be rare to need 4 circs and 4 mixing valves to cover your radiant demand. I'm no expert but others here are and can help you get it right.