Changes needed to use 3/4" pex

uppersouth

We are building a small home in central MN, 1000' sq ft plus a loft, we had a system designed using 2/2" pex-al-pex. But have been given 3 500' rolls of 3/4" pexflow. Can anyone give info as to what we need to change. We are pretty handy, my husband is in construction and I'm a retired mechanical drafter. We are on a very limited budget as I'm living with cancer.. any info. Would be appreciated.

GroundUp

2/2" PAP? You mean 1/2" or 1"? 1500ft of 3/4" for a 1000 sq ft slab is way overkill, or will the loft have underfloor radiant as well? I'm also in Central MN and would be willing to chat or take a look at the project if you'd like, I've been doing hydronic heating for 11 years

uppersouth

Meant 1/2" yeah, I figure some of that will go for a future garage. I was given the 3/4

GroundUp

So.... what are you asking?

uppersouth

I had a system designed but it's for 1/2" pex all pex.. I will be using the 3/4" so I'm trying to figure out what else needs to change in the panel as well as the layout because of the different pex

GroundUp

You were given 1500ft of 3/4" so you don't need to buy any 1/2" PEX is what you're saying? Pexflow is made in both barrier and non-barrier. If it's non-barrier, don't use it. 3/4" can run longer loops at a wider spacing than 1/2" can, so if your 3/4" is oxygen barrier, I would personally run 2 loops at 400 ft long and 15" OC with what you have which is still overkill but will work well with low water temps. You'll need different manifolds (or make them from copper or steel) to accommodate the larger tubing, but otherwise everything remains the same.

uppersouth

Yes, it's pexflow 02 barrler tubing

uppersouth

So there would be no difference in the pumps? I would still use the same ones quoted for 1/2"?

Rich_49

Is this tubing to be embedded (in concrete or other) or below / above floor ?

15 " spacing IS NOT conducive to even floor surface temps , nor does 3/4" tubing deliver more BTUh than 1/2 " . 3/4" does decrease the resistance and can be run longer in loop length , however , this is not always a good thing dependent on what type / size circ is planned .

Could you tell us what type install was planned ? Tell us a bit more about how it was to be zoned , controls .

Using the 3/4" in the garage at a wider spacing makes more sense than widening spacing in the living area .
If someone wanted to give you a pick up truck for free but you have nowhere to park it or no practical use for it are you obliged to take it and use it ?

uppersouth

It will be in a slab, as we're building a slab home. So are you saying you wouldn't recommend using the 3/4" ? Kind of why I'm asking is if I can make the 3/4 work or not and if I can make it work what are the differences

DZoro

Do the same as 1/2"
300', 12"oc, don't need a large pump
Like to see the very outside loop 6" oc then 12" the rest of the way.

uppersouth

Hopefully this helps a little

uppersouth

Also this

uppersouth

Sorry, attachment didn't go

Zman

The 3/4" will have much less resistance than the 1/2" but will not put out much more heat. If you want to use the materials on hand, it would probably be easiest to cut the 500' rolls in 1/2 and do 4- 250' runs at 12" OC. If you have a big window wall with high heat loss, you could do 5-loops and run that area at 6"-8" OC.
With the 1/2" tube,you would probably run the circulator on speed 3. With 3/4" you should be able to run on speed 1.

GroundUp

I'm going to have to respectfully disagree with Rich on the spacing. We had a project manager back in the day that spec'd 3/4" for EVERYTHING due to the longer loop length and wider spacing (I urged 1/2" but had no say in the matter) and to my surprise, we scoped a new slab with 3/4" at 15"OC right next to an existing slab with 1/2" at 12"OC and found the heat transfer almost identical in terms of being even. The 3/4" actually heated to the center of the spread faster than the 1/2", but then mellowed out and stayed just as even as the 1/2". With higher water temps or shallow slab placement I can see this being an issue, but a typical staple down in a 4" slab and 90 degree water it's a non-issue in my travels.

With that said, I would still use 4 loops of 1/2" at 250ft if it were mine (not sure why your guy spec'd for 5 loops), but it sounds like you're determined to utilize your free tubing. Closing the spacing to 12" and making 500ft loops is certainly feasible, it will just create more work for the pump and lower your return temps a bit. I prefer short loops and even distribution myself, but to each their own

SuperJ

Make sure you insulate that slab really well, especially since you're looking at a electric boiler. Probably 4+ inches of rigid foam. Don't forget the edges and thermal breaks.

This often gets missed, and you can't change easily after the fact.

If the pipe and labor is free, I would run the pipe at overkill close spacing, especially around the outside and in bathrooms etc. It's nice having system setup for a low temp heat source upgrade from you electric boiler, like a GSHP, or a Modcon boiler one day. Tighter spacing equals more even surface temps and lower water temps. Lower water temps mean more efficiency with water to water heat pumps, and gas boilers.

Zman

I think @GroundUp is splitting hairs at this point. Unless everything is exactly the same, tubing depth, insulation ect. how did you determine the the 2 slabs performed the same? Did you use an IR camera.

There are tons of variables that effect output. Running 3/4" tubing 500' is going to cause a noticeable temp drop from one end of the loop to another. This will be far more noticeable than 12" vs 15" spacing.

To the OP. If you keep your tubing in the center of the slab (vertically), run 12" or less OC, and keep your lengths less than 400' (for 3/4") and use a minimum of 2" insulation under and at edges, you are guaranteed success in 99% of applications.

GroundUp

Zman yes, thermal imaging was used. Different project manager, different project, same building and same installer (me). Everything was identical aside from tubing- imaging started from room temp slab, kicked both control valves open at the same time and was monitored through a full heating cycle. I'll admit I was surprised myself, and this situation is why I ordered the imaging in the first place- to show the PM that he should consider 1/2" in the next one because "watch this". After scraping my jaw off the floor and enduring the smug stare from the PM, this information was added to my memory. I don't like it either, but it happened.

Brewbeer

If this were my project, I'd use the 3/4 in the exact same way you were planning to use the 1/2, and benefit from the lower pump energy that will be required.

uppersouth

Thanks everyone with the savings from using this free tubing I was planning on going with a dual fuel boiler figured I'd be better off that way then I can use some of the electric companies incentives up there but there's no natural gas in the area so it's going to be propane and Electric or fuel oil and electric and I swore no more fuel oil after having it for 28 years in the house we are in

SuperJ

I'd rule out fuel oil, go with the dual fuel propane/electric option.
With a small house, high efficiency boiler and 3/4" pipe you could probably pipe it primary only (no zone valves, on the major living areas to make sure the boiler has adequate flow) and run off a outdoor reset with a space sensor for high limit.
With fuel oil you'll need to protect the boiler from condensing, and be into more complicated piping/valves/pumps etc.

Rich_49

GroundUp said:

I'm going to have to respectfully disagree with Rich on the spacing. We had a project manager back in the day that spec'd 3/4" for EVERYTHING due to the longer loop length and wider spacing (I urged 1/2" but had no say in the matter) and to my surprise, we scoped a new slab with 3/4" at 15"OC right next to an existing slab with 1/2" at 12"OC and found the heat transfer almost identical in terms of being even. The 3/4" actually heated to the center of the spread faster than the 1/2", but then mellowed out and stayed just as even as the 1/2". With higher water temps or shallow slab placement I can see this being an issue, but a typical staple down in a 4" slab and 90 degree water it's a non-issue in my travels.

With that said, I would still use 4 loops of 1/2" at 250ft if it were mine (not sure why your guy spec'd for 5 loops), but it sounds like you're determined to utilize your free tubing. Closing the spacing to 12" and making 500ft loops is certainly feasible, it will just create more work for the pump and lower your return temps a bit. I prefer short loops and even distribution myself, but to each their own

Unless I missed it , we have no idea of the design spacing used for the 1/2" tubing . Most of my designs for indoor residential use in a slab application are no wider than 9" . Thus my comment about a 15" spacing since I would only entertain a 12" spacing in an interior area like a hallway or similar where people pass through rather quickly .

Maybe the OP could clear up the original spacing for us so we can offer the best advice

uppersouth

I've been looking for the drawing and can't seem to find it at the moment. I'll keep looking...

hot_rod

larger id may require higher flow rates to keep velocity adequate for air removal.
The load calc and design info from any of the radiant programs would show if it is doable. It would be wise to have the load calc and design info before you start tubing.

Not so easy to work 3/4 pex to tight spacing. Keeping the tube warm will held forming the loops and bends