PEX under car parking?
Last Post 17 May 2022 12:38 PM by sailawayrb. 9 Replies.
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sirron1957User is Offline
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02 Apr 2021 02:31 AM
I hope you can help me. I've searched and have not found direct info for a project I'm doing this summer. I'm finally going to be building my woodworking shop this year and will be putting in radiant hydronic in floor heating. There will be a garage door enabling me to park my car inside during winter when bitter cold temps hit. There will be 2" of polystyrene insulation under the concrete, the PEX tubing will be on that using styrofoam clips with 4" of fiber reinforced concrete above that. Is it safe to route the PEX under the portion where the car will be parked? Thank you for any info that can be provided,
newbostonconstUser is Offline
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02 Apr 2021 02:30 PM
Yes the pex in concrete under a parked car is fine. This is how they do heated roadways and driveways. Just a note it takes at least 6 hours to get a building up to temp using heated floors. So unless you are going to continually heat the building you are wasting your money. Mini Splits are a better way to go.
"Never argue with an idiot. They will only bring you down to their level and beat you with experience." George Carlins
sirron1957User is Offline
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03 Apr 2021 12:08 AM
Thank you for your reply and I looked into mini-split but have been told by people in this part of the country it's not enough that I would need to have some other heat when the temps dip to -15 or lower, especially when the wind blows. That's when I started looking at PEX. And yes, I plan on having it going all the time to a minimum of 50 and another source of heat, garage heater or wood stove, to bring up to temp when I want to work. But in all reality I'll be out in the shop almost every day :)
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03 Apr 2021 01:46 AM
Use slab temp sensors so you can keep PEX from freezing. You can use glycol too, but it significantly reduces heat transfer/emitter efficiency and also significantly increases hydraulic friction head loss and pump size.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
GoGreenSeleneUser is Offline
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09 Apr 2021 10:27 PM
Posted By sailawayrb on 03 Apr 2021 01:46 AM
Use slab temp sensors so you can keep PEX from freezing. You can use glycol too, but it significantly reduces heat transfer/emitter efficiency and also significantly increases hydraulic friction head loss and pump size.


While I agree with your comment, I would say that glycol gets the job done pretty efficiently.
sailawayrbUser is Offline
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10 Apr 2021 05:22 PM
Maybe efficiently enough...but significantly less efficient than if you don't use glycol.
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GoGreenSeleneUser is Offline
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16 Apr 2021 09:07 PM
Posted By sailawayrb on 10 Apr 2021 05:22 PM
Maybe efficiently enough...but significantly less efficient than if you don't use glycol.


I don't know. I mean, I perfectly understand those who don't like using glycol, but it is a fact that this one is extremely efficient.
sailawayrbUser is Offline
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17 Apr 2021 12:21 AM
What one is extremely efficient?

Propylene glycol is the only one to use. If you have a slab freezing risk, then you use the appropriate % glycol/water mix and you lose efficiency which you account for in the design. If you don't, you don't. The answer isn't driven by what you like or opinion.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
CleanBuilding1975User is Offline
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16 May 2022 08:51 PM
I agree glycol is efficient but that is because it is the only option, correct?
sailawayrbUser is Offline
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17 May 2022 12:38 PM
Glycol is NOT efficient. It significantly reduces heat transfer/emitter efficiency and also significantly increases hydraulic friction head loss which increases your pumping requirement/size and associated electric usage. So don't use gylcol unless you absolutely have a real freezing risk. Propylene glycol is the only glycol you can legally use in a hydronic radiant system.

Ethylene glycol is a poison and is not allowed because of the potential of getting into the domestic water supply. A backflow preventor device should also always be used if the hydronic radiant system is physically attached to the domestic water supply...say when a fill/purge valve is permanently installed between the hydronic radiant system and a cold water domestic water line...even if you don't use any gylcol at all.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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