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.