Would you connect PEX-AL to PEX A ?

moots · August 2022

Hi everyone:

I have a small zone of around 150' staple up PEX-AL tubing. I plan on tapping into this zone to a pair of Slant-Fin baseboard heaters in a small room with around 150' PEX-A Uponor loop which I have already roughed in. I did this before I noticed the zone I wanted to tap into uses PEX-AL. I am leaning towards ripping out the old PEX-AL which would take a day or should I figure out how to connect the two types of PEX through compression or however it could be done ? (How do you transition between the two types?). I understand it's not a good idea to mix PEX types but I am a DIY homeowner so no exposure here.

Thoughts ?

hot_rod · August 2022

Yes you could connect them. What brand and size is the PAP? Do you have a tool to crimp it? If not a compression coupler would work. The PAP couplings often had brass ferrules to grip into the tube better.

moots · August 2022

Thanks for the response, the PAP is 1/2" and so is the PEX-A. I only have an expander tool for the A though..Do you only need one compression coupler ? Any specific type or just a standard compression coupler ? Supply House ?

EdTheHeaterMan · August 2022

You might want to put a hold on connecting Baseboard to radiant floor zone. You will be disappointed with the results

hot_rod · August 2022

Confirm what temperature that loop runs at, then look up the output of the fin tube you are adding at that temperature. If the SWT is say 150F, at a 15 delta the average SWT will be around 143F, that is the number to use.

Here is an example of a common SlantFin output chart.

So calculate how many feet of fin tube to get the output you need.

Officially the fitting you use for PAP should have an ASTM 1281 listing. Unofficially many universal fittings will work fine. Probably some of the box store compression fittings

Here is one from Pex Universe. This will have the gripper and o- ring insert for PAP and should fit the standard pex also, confirm with them. The o-ring insert is a big part of the seal on PAP.

Or buy two fittings and couple them together PAP by thread, same with pex. One male one female thread.

moots · August 2022

Thanks for the info Hot-Rod !

So currently my 250sq ft radiant loop has a mixing valve set to 3. Based on what you have provided me it seems adding in a pair of six foot Slant Fin Tubes connected together in a 340sq foot space and by turning the mixing valve off this would work for both rooms correct ? It's all 1/2 inch piping.

hot_rod · August 2022

Depends on the mixing valves you have. Caleffi 521 adjust from 85- 150F. The highest number gives you the highest temperature on any valve.

Guesstimate the load in that space at 8000 btu/ sq ft?? Maybe 20- 25 btu/ sq ft.!

8000 divided by let say 350 btu/‘/ hr would need 22’ of fin tube

Ideally you crunch the load number for that space to better see what you need to supply

As you can see, hitting that circuit with 170F supply will drop the fin tube required

A panel radiator or high output fin tube may be a better option? Panel rads work around 140F pretty well, a nicer heat, closer to radiant than the fin tube.

moots · August 2022

Thanks for the information Bob !

I understand the load calculation requirements better now and I have already mounted 12' of Fin Tube FYI.

My three way mixing valve is a Caleffi set to 3 for the existing radiant loop which usually runs around 140 degrees on the return at the NTI boiler which avoids the condensation issue.

My question is if I connect into this zone "BEFORE" it gets to the radiant loop the Fin Tubes will receive the hot water necessary for that circuit.

Then the water makes it to the radiant loop at a lesser temp of course.

So with this scenario it sounds like the radiant loop will not perform as well but with that loop it's not critical for heat so as long as it gets a bit warm it would be ok.

Ideally the solution is to create a new zone for the 12' of Fin Tube and be done with it but a bunch of work would have to be done on the manifold piping, electrical and such which I am trying to avoid.

Also the Fin Tube room has a refrigerator in it which cranks out some heat.

final thoughts ?

Best regards...Dave

hot_rod · August 2022

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

once we know what you need, then it will be easier to decide the best or how much heat emitter you need m.

You are limited by the 1/2” tube as to how much heat energy you can move. So determine the load of all the spaces on that 1/2” loop. The loop being only 150’ will help.

Yes to supplying the radiator first then the radiant floor

12’ of fin tube running at 140F may not be enough? 350 btu/hr per foot of fin tube at 140. Approximately, depending on what brand and model of fin tube you have. They all have output charts online.

Ironman · August 2022

Good advice about the output based upon the SWT.

Relating back to the fitting question: the simplest thing when you have different piping combinations is simply to thread a male adapter from one type into a female adapter from the other type. That way you use the correct fitting for each type.

Male and female; it still works in spite of what the lunatics of today think.

Would you connect PEX-AL to PEX A ?

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