3/4" PEX Tubing - In Slab

[Backlight]

I'm currently building a garage (posted in the gallery section - Link) and have a question regarding PEX tubing for in floor heat.

I had the heat loss calculations done, the designer is calling for 3/4" PEX in the slab and 1/2" on the second floor. There are 5 loops in the slab 6" apart in the outer perimeter and 12" apart in the center..

Question - is 3/4" normal for in slab? I'm just east of Ottawa in Ontario Canada. Looks like 3/4" is quite a bit more costly than 1/2" or 5/8". Further PEX Universe does not carry 3/4" Adapters for the manifold sets.

 

[anthony666]

I'm currently building a garage (posted in the gallery section - Link) and have a question regarding PEX tubing for in floor heat.

I had the heat loss calculations done, the designer is calling for 3/4" PEX in the slab and 1/2" on the second floor. There are 5 loops in the slab 6" apart in the outer perimeter and 12" apart in the center..

Question - is 3/4" normal for in slab? I'm just east of Ottawa in Ontario Canada. Looks like 3/4" is quite a bit more costly than 1/2" or 5/8". Further PEX Universe does not carry 3/4" Adapters for the manifold sets.

if that's what the heat load requires, yes .. it's not very common though, usually when you are working on massive buildings and the runs are over 350 feet, or there's no insulation in the building

who did you work up ??

 

[Backlight]

if that's what the heat load requires, yes .. it's not very common though, usually when you are working on massive buildings and the runs are over 350 feet, or there's no insulation in the building

who did you work up ??

Runs are all under 300', building is 32'x32', all walls are R22 and have R40 - R50 in the attic, R17 doors... Heat loss is ~42,000BTU with a -11F design assumption... Need to go back and ask some questions I guess.

 

[Blk88GT]

Something doesn't seem right!

 

[anthony666]

Runs are all under 300', building is 32'x32', all walls are R22 and have R40 - R50 in the attic, R17 doors... Heat loss is ~42,000BTU with a -11F design assumption... Need to go back and ask some questions I guess.

did you get design drawings ?? what's the boiler spec & a near boiler piping strategy ??

unless the water delivery temperature is incredibly low i can't see any reason for 3/4" pipe

 

[Backlight]

did you get design drawings ?? what's the boiler spec & a near boiler piping strategy ??

unless the water delivery temperature is incredibly low i can't see any reason for 3/4" pipe

Yes I have drawings.

Boiler load - 52,250 BTU/h
Total flow 5.7 GPM
Supply temp garage - 106F
Supply temp loft - 97F
50% glycol

I don't have a near boiler piping design, it was going to be two manifolds/zones, one for each floor.

Thanks for your input - this is not my day job so don't have a full view on accuracy.

 

[mygarageone]

I have installed many side walk , driveway and also a semi loading pad all in Mich.never once used 3/4". Nor was it. Ever called for in the engineered plans.
I would look into this if it were me.

 

[big.jim]

here in the uk 1/2 inch is normal for all slabs , manifolds unless big industrial set ups will only take 1/2 inch , never seen 3/4/used at all

 

[anthony666]

Yes I have drawings.

Boiler load - 52,250 BTU/h
Total flow 5.7 GPM
Supply temp garage - 106F
Supply temp loft - 97F
50% glycol

I don't have a near boiler piping design, it was going to be two manifolds/zones, one for each floor.

Thanks for your input - this is not my day job so don't have a full view on accuracy.

i think the slab delivery temp is the reason they spec'd 3/4" pipe .. email me the drawings/specs and i'll take a look if you like

[email protected]

 

[mygarageone]

i think the slab delivery temp is the reason they spec'd 3/4" pipe .. email me the drawings/specs and i'll take a look if you like

[email protected]

That is very low temps and would require more surface area. Wonder just how much more. Fuel savings they expect ?

 

[anthony666]

That is very low temps and would require more surface area. Wonder just how much more. Fuel savings they expect ?

i'm curious to see what kind of boiler they spec'd and what the return temps they expect to see .. or maybe there was a sale on mixing valves and they're looking to unload a few

seems silly to me

 

[mygarageone]

i'm curious to see what kind of boiler they spec'd and what the return temps they expect to see .. or maybe there was a sale on mixing valves and they're looking to unload a few

seems silly to me

Yes it doesn't make much sense. Unless they expect to see a Hugh fuel savings and I am doubtful .

 

[Backlight]

All I've had them complete is the heat loss and pipe layout, nothing else committed or purchased... Intent is to install the pipe (which I will do myself) before the slab is poured so I can install a boiler in the future.

I didn't think much of the 3/4" spec until I started looking at prices and availability of 3/4" pipe and manifolds and said, hmmm, something is unique about this...

 

[anthony666]

use 1/2" pipe .. only one perimeter loop instead of three and run the filler pipe length ways through the building, cuts down on the number of 180's in the tube

if you're gonna just rough it in tape up the ends of the tube .. unless you're running a mud wasp sanctuary

and for the love of god .. this guy did your design layout, even if it's weird, please PAY HIM .. i've done so much design work for free and had the client cheap out and install the pipe himself .. which is fine, by all means save a buck, just don't stiff the guy .. i'm not saying you would or are gonna, just venting and getting it off my chest .. my pet peeve

 

[mygarageone]

All I've had them complete is the heat loss and pipe layout, nothing else committed or purchased... Intent is to install the pipe (which I will do myself) before the slab is poured so I can install a boiler in the future.

I didn't think much of the 3/4" spec until I started looking at prices and availability of 3/4" pipe and manifolds and said, hmmm, something is unique about this...

Two questions ? , are they supplying the pipe ? And did they give you a reason for using 3/4" ?.

I can not understand why they have your pipe working temps so low , they must have a reason. Find out !

 

[anthony666]

Two questions ? , are they supplying the pipe ? And did they give you a reason for using 3/4" ?.

I can not understand why they have your pipe working temps so low , they must have a reason. Find out !

you should see the tube layout .. one double exterior door, i think it's just a basement slab .. there's three perimeter runs before the filler runs .. i think the guy doing the inputs into the design program musta put a decimal place wrong or something

 

[Backlight]

use 1/2" pipe .. only one perimeter loop instead of three and run the filler pipe length ways through the building, cuts down on the number of 180's in the tube

if you're gonna just rough it in tape up the ends of the tube .. unless you're running a mud wasp sanctuary

and for the love of god .. this guy did your design layout, even if it's weird, please PAY HIM .. i've done so much design work for free and had the client cheap out and install the pipe himself .. which is fine, by all means save a buck, just don't stiff the guy .. i'm not saying you would or are gonna, just venting and getting it off my chest .. my pet peeve

He's been paid Just hope he's still keen to answer my questions.. lol. There was never an intent to have them do any install work or for me to purchase anything from them. That was communicated up front and we agreed on a reasonable price for the design work.

Will install a manifold so I can keep the pipe under pressure during the slab pour - gonna do this right!!

What would a standard supply temp be? I'm going to go back and ask why he used what he did...

 

[mygarageone]

you should see the tube layout .. one double exterior door, i think it's just a basement slab .. there's three perimeter runs before the filler runs .. i think the guy doing the inputs into the design program musta put a decimal place wrong or something[/

Maybe he owns the supply house ?

 

[Backlight]

you should see the tube layout .. one double exterior door, i think it's just a basement slab .. there's three perimeter runs before the filler runs .. i think the guy doing the inputs into the design program musta put a decimal place wrong or something

It's a garage slab, there are two overhead doors as well - see the pics in my build thread (link in the OP).. Not that this really changes anything, something is still off

 

[anthony666]

He's been paid Just hope he's still keen to answer my questions.. lol. There was never an intent to have them do any install work (at least not now). That was communicated up front and we agreed on a reasonable price for the design work.

good man .. sorry, was just venting .. i ran into a guy at the beer store last week that i'd done a qquote for, i was in my truck on my way home when it occurred to me why he was looking so sheepish

Will install a manifold so I can keep the pipe under pressure during the slab pour - gonna do this right!!

pressure test it .. the let all the air out .. let the slab cure then test again

it's easier and better to fix it after the fact .. the guy running the pour is not gonna sit around with a half load of concrete in the truck paying his guys while you do a repair and retest it .. not to mention what happens to the two gallons of concrete that gets splattered throughout your building if it lets go .. the damage is only ever where the lip of a wheelbarrow pinches a tube , so a) get them to use a chunk of plywood when they tip to spread the weight and b) do not use cheap china made heat pex

you can narrow down a leak by listening, then pinpoint it with a bucket of soapy water & watch for the bubbles

What would a standard supply temp be? I'm going to go back and ask why he used what he did...

i reverse engineer the delivery temp based on what the boiler manufacturer wants the return temp to be .. probably somewhere around 120 going in .. but it hinges on so many factors it's hard to be specific

 

[Mr onetwo]

Get a new designer....1/2" will do that building easily.Trust me, you don't want to wrestle with 3/4"

 

[GYPSY400]

Get a new designer....1/2" will do that building easily.Trust me, you don't want to wrestle with 3/4"

X2.. unless the designer made a typo.


Also to the Op.. did you insulate under the pad? The last pic I seen of the floor has gravel up to the door thresholds, and not a whole lot of foam around the perimeter.

Sent from my SGH-I747M using Tapatalk

 

[Backlight]

X2.. unless the designer made a typo.


Also to the Op.. did you insulate under the pad? The last pic I seen of the floor has gravel up to the door thresholds, and not a whole lot of foam around the perimeter.

Sent from my SGH-I747M using Tapatalk

Yup - R10 under the slab. Not sure why you would need more foam around the perimeter? Intent is of that is to create a thermal break between the slab and the foundation wall.

 

[big.jim]

foam around the slab is for expansion , typical supply temp for slab is 40-45c to maintain a room temp at 20c

 

[anthony666]

foam around the slab is for expansion

maybe where you come from, here it's to prevent heat loss

and supply temp depends on way too many factors to even ball park it .. the climate in jolly old england is tropical compared to ottawa

 

[sands35]

Runs are all under 300', building is 32'x32', all walls are R22 and have R40 - R50 in the attic, R17 doors... Heat loss is ~42,000BTU with a -11F design assumption... Need to go back and ask some questions I guess.

For reference, I have a 26'x32' garage, granted one floor.

2" XPS under slab and 3" EPS around the perimeter. It is a monolithic slab with 42" footers (don't ask, just the way the contractor did the job).

I have a takagi jr tankless heater (140k BTU as I recall) 4 loops of 1/2" at ~195 feet each. It keeps the garage at 50*F with no problems with a single digit ambient. It will take the ambient temp from 40*F to 50*F in 30-40 minutes, no problem. (which tells me that the heater may be oversized - but it's the smallest nat gas powered one I could get).

R13 walls and R30 ceiling.

 

[mygarageone]

For reference, I have a 26'x32' garage, granted one floor.

2" XPS under slab and 3" EPS around the perimeter. It is a monolithic slab with 42" footers (don't ask, just the way the contractor did the job).

I have a takagi jr tankless heater (140k BTU as I recall) 4 loops of 1/2" at ~195 feet each. It keeps the garage at 50*F with no problems with a single digit ambient. It will take the ambient temp from 40*F to 50*F in 30-40 minutes, no problem. (which tells me that the heater may be oversized - but it's the smallest nat gas powered one I could get).

R13 walls and R30 ceiling.

That unit should modulate down as your water temp rises. You would have been hard pressed to find a boiler lower than 40,000 btu's

 

[GYPSY400]

Yup - R10 under the slab. Not sure why you would need more foam around the perimeter? Intent is of that is to create a thermal break between the slab and the foundation wall.

Ok, understood.. as long as you have some insulation to protect the inside from the outside temperatures you should be ok.. my pad is a little different being a mono slab.. it is totally covered around the stem wall on the outside with 2", and the entire bottom is also 2", thickened perimeter and all.. no where can you see cement from outside the building.
What you dont want is the slab heating the soil, especially near the surface.

Sent from my SGH-I747M using Tapatalk

 

[Backlight]

Heard back from the designer - he said 5/8" works in the model but not 1/2"..

 

[anthony666]

Heard back from the designer - he said 5/8" works in the model but not 1/2"..

5/8's is snow melt stuff .. the fittings are not cheap or common .. why does 1/2" not work ?

 

[Backlight]

I could still use more detail, I caught him on the phone quickly (I was in and out of meetings). I think but won't quote he said 1/2" is good for 30 watts a square foot and my heat loss is higher as a result of the air leakage on the doors.

Maybe he is designing as a 'living space', able to sustain 22C where most would not design a garage to this assumption.

 

[mygarageone]

5/8's is snow melt stuff .. the fittings are not cheap or common .. why does 1/2" not work ?

You got that right.
I did a job for Ice Mtn water some years ago , was. Working fora southern mechanical contractor.
There was some damage to several of the loops from some idiot drilling holes in the concrete for special sensors. Needless to say several holes.
Anyhow , my boss says just go down to the hard ware store and get what ever you need . I told him this stuff was not store shelf items. Because he didn't
Want to hear it , he went him self and bought a whole bunch of regular water black poly pipe and fittings.
I told him it wasn't going to last but he said it's not my problem , so I let them do there thing and was layer off a wk later. Never heard what happened after that but I can guess. By the way , there boilers were cast iron units with no tempering valves.

 

[Mr onetwo]

Get a new designer....1/2" will do that building easily.Trust me, you don't want to wrestle with 3/4"

Like I said...get a new designer!

 

[Modoc]

What about control joints in a slab with pex tubing in it ?

 

[Randy in Maine]

What about control joints in a slab with pex tubing in it ?

No problem. The joints are just cut so that they do not cut the PEX tubing.

In my case the slab is 6" thick with the 1/2" tubing attached to 6x6 woven wire on top of the insulation. The control joints are about 1/2-3/4" deep.

And I agree you want 1/2" PEX in the slab. I did use 3/4" PEX tubing to get the hot water from the boiler to the garage 4x250' loop manifold though. It is about 35 feet or so. The installer told me that 3/4" tubing will transfer upto 75K BTUs per hour andwould easily feed the system.

 

[anthony666]

this is applicable to you sir http://www.garagejournal.com/forum/showthread.php?t=234148

 

[Backlight]

this is applicable to you sir http://www.garagejournal.com/forum/showthread.php?t=234148

Thanks