New garage radiant floor

Hennessy82

Hey all, I'm helping my brother with his garage build. It's at the point of trying to figure out the heating. What we have so far is a 1000 Sq.ft garage with 4" rigid foam under the concrete with 4 loops of 1/2" pex B that are around 250' each. Exterior is zip sheet with 4" rigid foam. Natural gas is piped too. Also need hot water for utility sink. Located in Northern NJ. Trying to save room is a big consideration when thinking of a system. So I start looking at tankless and making a system using a DH tankless for radiant floor and the utility sink. But also looking at a combi or a wall hung boiler. But they seem to be a little over kill for our needs. Needless to say, I'm going in circles here trying to figure out which direction to go. My ruff estimates are something like this. (I think!) looking a 3 GPM with the 4 loops and need around 30k btu. Any info or insight would be greatfully appreciated! Just trying to wrap my head around all of this.

leonz

How was the foundation constructed?

Was reflective foam board used in the slab?

Was a vapor barrier installed under the reinforcing mesh?

Aggregate concrete mix?

Sand mix concrete?

Was the concrete vibrated in?

Was the garage floor slab covered with a canvas tarpaulin and straw and kept wet for 2 weeks to allow a slow curing rate?

Simple slab on grade with reinforcing mesh?

Simple slab poured neat below grade with no footer?

Reinforced slab poured against a hollow core cinderblock laid on concrete footer poured neat in trench with no forms?

Reinforced slab poured against a solid concrete footer poured in a form that rests on a solid concrete footer poured neat or poured in a form?

Was the footer extended above grade to allow the sill to be attached above grade?

Does the footer have a perimeter drain?

Does the footer have perimeter foil backed insulation glued to it?

How much insulation is in the walls? Is it batt insulation or spray foam?

Are 2 layers of fire resistant sheet rock used in the garage walls or ceilings or is corrugated steel used for a wall and ceiling cover?

How much insulation in the ceiling and what type of insulation is it?

How many windows?

How many man doors?

Is the floor heat extended on to the concrete apron approach?

hot_rod

knowing the heat load would be helpful. Typically .50-.65 gpm for 1/2” loops

If it is down in the 20,000 range a tank type water heater could be an option.

If it is just a hand sink a small under counter 6-10 gallon 120v tank may enough

Smallest mid con is 50,000, smallest combi around 110,000. Both would turndown to 8-10,000 btu:hr

Is cost the determining factor? A mod con would be the most efficient option

DCContrarian

You should separate the heating from the hot water, which complicates using the same device to provide heat for both.

How much hot water do you need? If it's just for hand washing a small electric tank would be enough and would simplify things.

hot_rod

I put a number of these in early on. Heat and DHW from one tank, legally :) 65,000 BTU input. Side wall venting is sometimes a nice feature.

They have gotten $$. What hasn't.

Hennessy82

Back at it, got sidetracked a bit. @leonz here's a little more information on the garage.

Poured footing at 36" below grade CMU (some cores filled at rebar from foundation sill plate anchors) foundation wall brought 2 course above slab with 4" Atlas Energyshield Foil facing towards the exterior. Slab on grade composition as follows, 5" Slab,vapor barrier, 4" Atlas Energyshield Foil facing down, 6" crushed stone, 12' x 6' x 1' footing in center(no insulation between footer and slab) for car lift. 1/2" pex b encapsulated in bottom 1/3 of concrete slab attached to wire mesh reinforcing. Concrete aggregate with calcium add mix due to temperature during the pour (Fast cure), covered and wet over a week and a half. Vibrated and trowel smoothed.

Walls above grade are 2x6 with R-19 Kraft face batt insulation in the cavity with a zip sheathing air and vapor barrier on the exterior. I also have 4" Atlas Energyshield Foil facing inward on the exterior of the wall with joints tapped. The hardiplank siding is attached to 1" furring strips that are secured back to the 2x6 studs. The Cathedral ceiling is vented with baffles to the ridge beam with R-30 Kraft face batt insulation at the exterior. 3 insulated garage doors (2) 8'x8' and a 10'x10', (6) tilt and swing pvc windows with thremal decoupling design. The walls have 1 layer of 1/2" gyp.

Having answered and given the specifics of the footing, flooring, wall, and roof configurations and based on what I have research. 25 BTU's per SF would be appropriate. So the system would have to be 25,000 BTU's as a starting point and I am leaning towards a combi unit that would also supply hot water to the sink. Seems like any unit I buy are well over 25k BTUs. I'm also going to keep it between 50-60 degrees and am not looking to wear shorts and a Tee in the winter...

What Combi manufacturer do you guys like and what setups have you guys used successfully? Looking for some advice and recommendations to point me down the right path!

Kaos

Many moons ago I did a garage to studio conversion that was about half the size you are looking at. Colder climate and nowhere near that level of insulation. The whole thing is heated and cooled by a 1 ton minisplit with a BOM cost under $1k. The operating cost is so low (~$20/month in the winter) that don't even bother to turn the heat down much when not in use. Recovery is quick as it only needs to heat the air. No water, no leaks, no glycol. Bonus, excellent AC in the summer. If you are doing dusty bits, you can get one of the slim ducted units and mount it like a shop heater on the ceiling without any ducts with a big filter on the intake.

The idea of hydronics and heated slab is all nice a good, but if you look at the BOM cost of the equipment plus all the bits, even with cheap gas, the ROI is never.

If you must have hydronic, I would do a small power vented tank with plate HX to tap it for space heat. The combi tank @hot_rod mentioned is nice but way too expensive. Your load is low enough that you can use a cheap recirc pump with a small plate HX on the potable side and small circ on the space heat side.

DCContrarian

https://forum.heatinghelp.com/discussion/comment/1873547#Comment_1873547

This seems like a spot for one of my favorite adages: an ounce of insulation is worth a pound of hydronics.

Dave Carpentier

Love how fast the floor dries with in-floor heat. For quick in/out task, I just squeegee out any slush while the door is open.

I made the mistake of a single loop of 1/2" in the 30x19 slab so it's slow to add new heat, but we poured it 6"+ so it's got a lot of thermal inertia. Still, it takes a bit to warm the air back up after the door has been open for a bit (usually wearing a hoodie). One of these days Im going to run a new line from the house boiler to a wall mount unit heater to help with that.

So I guess Im saying in your piping, allow a spare tap-off point for possible aux heat in the future.