Radiant in slab heat required components

[dg55117]

Hello -
New here but I've read everything on in slab radiant heat. But I have a few hopefully simple questions. Never mind if the system in under/over designed...I have what I have and I just want to get it to work as best as I can given the facts that already exist. It doesn't need to be a work place but just a heated garage for the cars so a minimum temp is all that is required

FIrst the details-
I just bought a house which had a new garage build and a radiant in slab heat for the detatched garage but it was only partially installed/finished.
-780 sqft, well insulated- closed cell spray foam, 2 inch hard pink insulation under and all around slab
-3 loops (280ft ea) of 1/2 inch ox barrier PEX to 3/1 manifold with 3/4 PEX out/in manifold and a 3 speed circ pump 1/25 hp connected to one of the manifolds with a shut off valve before going to the 3/4 PEX to manifold.

-now the questions...I only have electric available for heat, and with current wiring(which I'm not willing to change) I can only have a 9KW electric boiler/heater. So, aside from selecting a brand/type 9Kw boiler what else do I need and what is the order of the parts coming from the heater to the circ pump?
Do I need an expansion tank, do I need a vent or air remover, temp gauge , presssure gauge? In what order do I place the parts?
Thanks for any help as I can't find reliable consistent suggestions.
Thanks
Dave

 

[Rickcnc]

This is the simplest set up I would go with.

http://www.garagejournal.com/forum/showpost.php?p=1295204&postcount=122

 

[dg55117]

Thanks...that is what I needed.
However what is on top of the exp tank? A vent or pressure relief?
And to the rt of the tank, what is that thing??

 

[Rickcnc]

little more info

http://www.garagejournal.com/forum/showpost.php?p=2832231&postcount=6

 

[Highbeam]

That is a great, simple setup, but also a small setup. Your system will be scaled up and will of course cost more.

You say you can run a 9kw boiler. 9000 watts times 1.25 (required on this permanent appliance) is 11250 which divided by 240volts is 46.9 amps. I don't think you have a 46 amp breaker but if you have a 50 amp breaker than you are fine with 9000 watts. That's what is required for a 9kw boiler. A 40 amp breaker can only service a 7700 watt boiler which means a 7kw hydroshark or similar.

 

[dg55117]

Thanks guys. Yes, I have a 50 amp breaker.. not 40 -don't know what I was thinking as I calculated what I needed for the 9kw heater at 46amps too.
But, I do have another question... connecting all the components.. can I use the 3/4 pex or does it have to be copper? I have a few bends to go around and the pex would make it so easy.
Thanks
Dave

 

[Highbeam]

But, I do have another question... connecting all the components.. can I use the 3/4 pex or does it have to be copper? I have a few bends to go around and the pex would make it so easy.
Thanks
Dave

Great question. I have been working with 3/4" pex with crimp rings and it is wonderful. The pex offers no rigidity to hld all your components up on the wall so at the least you would have to support everything with brackets. The next concern is that near the boiler, heat could be high. The codes don't allow pex within 18" (?) of a water heater either so I can see an 18" chunk of something other than pex near your boiler.

I'm watching this thread to see what some pros might say, the pex would make near boiler piping much easier.

 

[jvitez]

dg55117: can you give us a bit more info? Where do you live? Climate makes all the difference in HVAC advice. What about the garage ceiling insulation, present or not, R-value? Are your garage doors insulated? How many and what type of windows? What temp do you want to keep the garage?

If the previous owner went to expense of spray foam insulation I'm assuming the rest of the space is well insulated and sealed. If so, a 9kw electric heater will give you 11.5 watts per sq ft, which is a reasonable ball park number as long as you don't live in Siberia and you're not opening the garage doors multiple times a day.

I know, HVAC pros will say get a heat loss calc which is the proper way to do things, but there's little downside to an oversized electric heater, and if too small it simply won't keep your space heated to the temp you want. But if you want a minimum temp to keep your cars warm your heating load shouldn't be onerous.

 

[jvitez]

Great question. I have been working with 3/4" pex with crimp rings and it is wonderful. The pex offers no rigidity to hld all your components up on the wall so at the least you would have to support everything with brackets. The next concern is that near the boiler, heat could be high. The codes don't allow pex within 18" (?) of a water heater either so I can see an 18" chunk of something other than pex near your boiler.

I'm watching this thread to see what some pros might say, the pex would make near boiler piping much easier.

This may be a Canada vs US code issue, but here we can plumb PEX right onto electric water heaters, only fuel burning water heaters need 18" of copper due to the high temp of the flue, not the heat of the water heater itself.

But, using copper is probably the best thing to do right at the heater connections specifically for it's rigidity. Make everything neat, strong, and stable close to your electric heater, then connect PEX to that.

 

[anthony666]

you can build an entire system in pex, but when it gets hot it expands and sags and generally looks like saggy **** .. also when calculating pipe size, pex ID is smaller, and even smaller still at the fittings, than same size copper and therefore the flow rate is way less in comparison

here in ontario the inspectors want to see 18" of non-pex piping from any heat source

 

[dg55117]

Thanks all,
The garage is well insulated and in Minnesota - so not Siberia but it doews get cold. It won't be a shop but I would like it to keep the cars and other toys warm in the winter and available to work on cars if I need to without completely freezing. It is well insulated but I don't know the value. The ceiling is rocked and above has over a foot of blown in fiberglass and the walls are spray foamed. It has 2 inch pink rigid foam around the slab and block. Insulated big door and service door with no windows.
I hope my 9kw/30K BTU heat system will be adequate.
I now understand that for astetic reasons and simple solid(ness) I should use 3/4 copper out and back to heater but I think I'll continue the PEX around some obstacles- they will be vertical runs so the sagging shouldn't be an issue.
I can't thank everyone enough as I got some great advice. Hope I ca nget it running this weekend.
Dave

 

[dg55117]

One more stupid question:
How do I fill the system with water/antifreeze?
I don't have running water supply in garage.
Thsnks

 

[CARS]

One more stupid question:
How do I fill the system with water/antifreeze?
I don't have running water supply in garage.
Thsnks

You wont want to run just water. You will need a anti-freeze. I think mine is called Glycol. I am sure you can run a hose from the house somewhere. Hydrant, washing machine, etc.

I used a sump pump and a bucket to add my antifreeze to the water. It wasn't an exact mix but the installer felt confident on ** amount of antifreeze to ** amount of piping, boiler capacity, etc.

 

[anthony666]

if you pump glycol into the system and then try pushing the air out with a garden hose setup first thing that spews out is your lovely glycol .. plus because glycol is so viscous it's a real ***** to pump unless it's cut

i have a veissmann flush cart now thats reasonably light weight, but originally i used a home made version, basically it was a $5 well jet pump from a yard sale on 2 wheel dolly with a reservoir that vented to atmosphere .. i set up my hose bib fill points on either side of a ball valve so i can recirculate the liquid in the system back into my reservoir with washing machine hoses where the air escapes .. i dump the appropriate amount of diluted glycol in the reservoir first and then add water as needed .. voila

 

[jvitez]

12" of blown in fibreglass, spray foamed walls, with insulated slab edges and foundation walls, and only Minnesota winters? Man, you're golden! Your 9kW heater should be plenty, especially if you only want to keep it at 50F or so. Again, little downside to a larger than needed electric heater, which is certainly not the case with fuel burning heaters.

BTW, compared to Minnesota I guess I'm the one who lives in Siberia.

 

[mygarageone]

You wont want to run just water. You will need a anti-freeze. I think mine is called Glycol. I am sure you can run a hose from the house somewhere. Hydrant, washing machine, etc.

I used a sump pump and a bucket to add my antifreeze to the water. It wasn't an exact mix but the installer felt confident on ** amount of antifreeze to ** amount of piping, boiler capacity, etc.

There is a simple way to test for this , take a small amount of the mixture from the system , put it in a container , and put it in your freezer , if it freezes , you know the answer.

 

[brokenknee]

There is a simple way to test for this , take a small amount of the mixture from the system , put it in a container , and put it in your freezer , if it freezes , you know the answer.

A freezer is only around 0*, it usually gets much colder than that in MN in the winter. I live in northern MN and a minus 30* is not uncommon for at least a few days a year.

 

[mygarageone]

A freezer is only around 0*, it usually gets much colder than that in MN in the winter. I live in northern MN and a minus 30* is not uncommon for at least a few days a year.

If it doesn't freeze at zero , I think you would be ok at -20 as it may trun to slush but nothing else.

 

[dg55117]

Thanks... I'm almost ready to fire it up.... just need to get that damn water/glycol mixture in there-

 

[CARS]

Thanks... I'm almost ready to fire it up.... just need to get that damn water/glycol mixture in there-

I'm sure that there is a proper way to do the mix. My guy just said ** amount of pex+boiler requires ** gallons of glycol. As I said, a sump pump works and I think 99% of us Minnesotans have one in our basement.

 

[CARS]

If it doesn't freeze at zero ,

Well, that is not entirely true. It freezes at zero in every country but the USA.

Odd metric people...

 

[dg55117]

Update on my system-i started this thread and got great advice.
All filled and air out, Taco pump, thermostat, exp tank, air eliminator all work great and no leaks. However my heater 9kw rheem elec. tankless only stays on for 15-25 minutes then shuts off. No blinking leds just shuts off. Cycle breaker and runs for another 20 minutes.
WTH? Are the heaters suppoded to fo that or is it defective? I can set my output temp to 130 no problem and output temp will get to that easily but it still shuts off after about 15-25 minutes.
Any help or ideas???
Thanks

 

[anthony666]

my initial thought would be over heat protection .. but cycling the breaker shouldn't let it run another 20 minutes or so .. check the manual and see what it say's on the subject

the other thing to consider is that maybe the thermostat is satisfied .. what it's set at ?? whats the temperature when the unit shuts down ??? maybe the t-stat is in a crappy location .. to rule it out jump across the t-stat terminals and see if it follows the same pattern

 

[dg55117]

Thanks... I don't see anything about over temp in manual or auto shut off. The thermostat controls the Taco pump and that never shuts off. The flow just continues. Since I just started up the system, the return temp hasn't risen at all yet... just sits at around 63 degrees. The output temp will stay at whatever I set it to ( 100, 110, 120 130) at least until it shuts off. Then the temp drops quickly as the Taco continues to circulate the fluid. Once I reset the heater, the output temp rises quickly to the set temp.
THe "green" led on heater(indicating on) stays lit but the red leds which indicate heater active go out.
Real odd-

 

[anthony666]

make a quick video of the system, stick it on you tube and link it here

show the components and how you set it up as best as possible

 

[dg55117]

I think I figured that the temp difference was to big and the heater sensed that it couldnt keep up and shut down.
I was setting it to 120 out and the input was only 60.
Now Im goung to try to slowly bring the slab up to temp by setting output temp to 90 until I get some heat into slab.
How long can it take to get the slab up to 70...80...?

 

[rburke65]

Did you ever get this figured out? and how long did it take to get your slab to " 70....80"....I assume that's degrees F.? Seems hot to me?