radiant heat ?s need help 😅

OhioSparky

so I built a garage with my dad (36x48) and I have 6 - 300' rolls of pex (orange) in 6" concrete(on 2" of eps foam) I have a 6 zone manifold from pex superstore and a NG tankless water heater (6gpm+). Water heater was originally bought by my dad for another project(not radiant heat related) and is now just spare parts. Problem is now I don't know the best/correct way to put this all together. We were wanting a closed loop with no domestic hot water. I'm trying to do this as efficiently as possible & want to make sure it's right the first time. this is my last attempt before trusting a local handy man 😅

Thanks in advance for any help or advice.

Zman

The water heater is not ideal, but probably workable.
You are absolutely going to want to pipe it primary/secondary.
The model of the water heater will determine the boiler pump size.

OhioSparky

Its a BOSCH Aquastar GWH2400ES-NG
its an older unit, but still new in box. Its been in his old garage for the last few years unused.

Zman

You need to find the pressure drop chart for the heat exchanger in that unit to determine the circulator size. I took a quick in the online manual and did not see it.

GroundUp

That's not a condensing unit so low-temp radiant isn't an ideal use for it, but it'll work until it doesn't. If I were doing such a thing, I'd use a Grundfos 26-99 circ on the boiler/primary loop to circulate a loop only through the water heater, then a Grundfos 15-58 to run the load. If space allows, try to get the air eliminator and expansion tank in the primary loop and just serve the load as a secondary via closely spaced tees in the primary.

OhioSparky

I have as much as much space as needed. I'm building this on a 12' wall and then will enclose it in a utility closet once finished. is there a website that I can go to to help me understand better the lay out you guys are referring to?

and I really appreciate your help 😊

Jamie Hall

www.caleffi.com. What those guys don't know about hot water and radiant really isn't worth worrying about... one of their top men, @hot_rod , posts on here pretty regularly, but there is a wealth of information (look under the "Education" tab) on their web site.

OhioSparky

would we be better off purchasing a different heater? ultimately I'd like to keep operating cost as efficient as possible, but trying to keep install price low at the same time. I understand this is hard to do, but there's a lot more things to do and we are trying to build out of pocket.

GroundUp

If you just Google "primary/secondary boiler piping", there is a lot of good reading out there on the subject. Water heaters do not have an "H" Stamp from ASME, certifying them as a heating appliance, so most inspectors will not allow them if this is a place that gets inspected. They are also designed to heat water 50-70 degrees as it passes through the heat exchanger while the appropriate delta through the radiant floor is typically 10-20 degrees so a real boiler would be a better choice, but it's also a fairly large expense. We don't like to see water heaters used for space heating as they're not the "right" choice, but with all that aside they do work and there are thousands of them that have been in service for many years. You would gain 10-15% efficiency by going to a condensing boiler, IF you have a drain to get rid of the condensate, but in all honesty if install cost is a factor I'd run what you have. It might last you 3 years and it might last you 23. You could always save up for that day and swap when the time comes, with minimal piping changes.

GroundUp

Something like this, if it makes sense to you. I like to use isolating pump flanges with drain valves for purging the system. The triangles inside the pump indicate flow direction. You can substitute the 24v stat and switching relay for a simple line voltage thermostat if you like, the water heater will activate with flow so any time the pump moves water, the flow switch will light the burner.

OhioSparky

That is awesome, Thank you! This is the current manifold setup I have. Would you suggest still getting the air eliminator? The manifolds have an automatic purge valves on both the supply and return.

Sorry for the silly questions, But I'm an electrician by trade and this honestly has been the most confusing/intimidating plumbing project I've ever done. Thanks again everyone. 😅

SuperTech

Yes definitely get an air eliminator. Microbubble resorber type such as the Honeywell Supervent are the best way to go. Air elimination is a necessity, no matter how much you purge, air will come out of solution in the water once it's heated.

GroundUp

Definitely an air eliminator, yes. I prefer the Honeywell Supervent variety personally, but any of the brass microbubble style will suffice. Webstone a close second. Many prefer the Spirovent but every one I've ever seen in service either is or was leaking. Personal preference.

OhioSparky

We have decided to purchase a boiler for our setup... (Will keep the Bosch for domestic hot water) and a local plumbing store has suggested an FTV-110 or an TRX-085
what's your guys opinions on these?

newguy2021

@OhioSparky I know this is a yr old, however im in the process of getting ready for concrete pour of my 36x48. Curioud on what you did for your tubing layout pattern? I have seven 300' rolls of 1/2" pex being delivered tomorrow. Debating on 12" or 10" spacing which will determine whether i do 6 or 7 loops/circuits. 

OhioSparky

my garage is technically one giant zone.... I'll attach a few pictures of how i drew it out and also what it looked like. *remember I'm an electrician*
so I ran 2" of eps foam with moisture barrier (on top of foam) rebar chairs with 1/2 rebar and concrete wire(probably overkill) the concrete wire makes it SUPER EASY to lay down your tubing (it's like graph paper) everything i read said tubing needs to be in the upper half of pad (closer to top of slab than bottom) so we zip tied it like crazy about every 12" so it wouldn't float to the top. we poured a 6" pad with 12" tubing spacing. i was told each zone should be close to the same length and afterwards was informed 6" spacing around outside edge of the pad... my 12 is working just fine tho 😉 but once again this was my first time. i will tell you that I will never build another garage without a heated floor... it is awesome!
*Also* if you plan on putting in a lift... make sure you make accommodations now and make sure you know how to anchor it 😉