Help with pex return in baseboard heat

Aastock

My home has OLD radiant heat in slab foundation which is leaking badly int slab. My only option is to abandon system and run baseboard. I have to run 80ft baseboard thru 6 rooms pretty much entire house perimeter. I am going to use pex. My supply house sells wirsbo I'm figuring 3/4 pex between units and I also have to put return line in baseboard. How am I going to fasten all the pex to keep in baseboard can this all b done?I am just very concerned about the return being in unit also and how I'm gonna keep it all in place in baseboards. Basically it's running around house and I'm gonna go right thru walls room to room with feed and return. Also I have an 6' area I have to go around ext. Door. Can I just chip a trench into slab, run the pex thru and mortar it back up? Any input or tips would be greatly appreciated.

mattmia2

you need to engineer it. Start with a heat loss calculation. The water will get cooler as it travels through the loop so you should have more element at the end than the beginning. You can get dummy baseboard cover for the sections that are not fin tube element. Most baseboard covers have hangers for a supply/return pipe through the top of the cover. The size of pipe will depend on the capacity it needs to be. 1" pex is about equivalent to 3/4" copper but it is pretty difficult to work with, you might be better off doing it in copper. At very least you will have to use fittings to turn the corners at 90 degrees.

read this:
https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_19_na.pdf

Ironman

PEX has too much linear expansion to use in that way. It will also get chafed as it expands an contracts causing eventual leakage.

Do it right and use copper. You'll still have to make some allowance for expansion, but it's minimal compared to PEX.

A 100' length of pex will grow 12" when its temp is raise 100*. Copper will expand less than 1" under the same conditions.

hot_rod

A few things first. Did you do a room by room load calc? Determine how many feet is required.
Remember with baseboard in series, you have a temperature drop along the circuit, the baseboard at the end of the loops need to be sized for that temperature drop.
80' would be way too long for a single zone, need to split that up.
If you do determine 3/4 pex can handle the load, consider buying straight lengths instead of coils, it would fit inside the enclosure much better.
Be aware pex expands quite a bit, grows in length as it heats up, you need to accommodate that on long runs.

hot_rod

https://www.slantfin.com/slantfin-heat-loss-calculator/

EBEBRATT-Ed

I agree with @Ironman copper is the way to go. You will never be able to support the pex. About 68' of 3/4 finned baseboard is all you can put on one loop

Aastock

So I guess pex is out, I'll have to run copper. Damn... This is just a family/donation/super budget job, they do not have much $ to work with. The blue lines are capped unused 3/4 lines that were put in yrs ago for future use they run right to furnace one can b feed and other return that's y I have to have return in base unit. The #'s in red on each wall are proposed lengths of actual element. I will have to fill each wall complete thou with dummy's for look, can't just have pipes in floor. That plan ends up having 50' of element total. I'm wondering if I should put more than an 8' element in  bed 1 it's the master near end of run. I know there's only a little in kitchen at end of run also but the play room addition is on the other zone and is open to kitchen, plus the pipes under cabinets are radiating heat also. Does this look like a decent plan? I'm gonna have to chip a trench in floor around door in living room, can I just run copper and cement it back up? Thanxx for all your help guys.here is a REALLY rough plan.

hot_rod

Maybe a tube like Viega FostaPex, it behaves more like copper. It does require a special strip tool

Aastock

Does that plan look decent to u?

Zman

Any pex-al-pex product would work well for this application.

Darek_NYC

I have a similar loop in my Upstate (NY) house. Run with PEX. It expands a lot and in many places the pipes hanging loose to absorb the expansion. The run over the exit door gave me a lot of trouble in my climate (sometimes -25F for multiple days) as the line froze even having more than 50/50 antifreeze if the system is off for a while. FYI my loop is 3/4 pex with multiple 90 deg. corners. The total length is about 100 ft and runs on 1/4 HP circulator without problems. Because of length and multiple curves the air might be trapped and gives you troubles.
Pex connects to the baseboards:


My pex connectors looks like this.

As others said, the copper will give you better look between the baseboards. While pex expands and curves It does not look straight on the wall.

Darek_NYC

And my loop looks more like that:

mattmia2

By the time you buy the fittings for the pex it is usually close to a wash with copper. Pex would be a better choice for the segment underground/in the slab. Sleeve it in pipe insulation to isolate it from the concrete. You could do the same with copper, but pex is more resistant to any movement of the slab.

Without doing the heat loss we can't comment on the appropriate size of the emitters.