Simple open loop radiant heat system

[Ryan Edwards]

Hello, my name is Ryan. This is my first post here. Hopefully, I'm posting this in the right section. I'm looking for some critique of my garage radiant floor heat plan.

I'm building an ADU in Renton WA. It has an 800 sq foot apartment upstairs and an 800 sq foot garage on the first floor.

In the garage, I already have three 100' loops of 1/2" oxygen barrier pex in the 4" slab, and a Rinnai ru80 152,000 BTU tankless water heater installed. I plan on using a mini-split heater upstairs. City water pressure is coming in at 74 psi from a brand new 1" water meter. I've never had problems with contaminants in the water supply.

I don't need heat in the garage very often it's really just a luxury, so I want to keep this system, as simple, compact, and cost-effective as possible. I don't care if it's not the most efficient.

It's an open system one zone I've opted to eliminate the mixing valves. The default temperature on the tankless is 140 I believe that should be fine for both the floor and potable use.

Will this system work, is there anything required that I'm missing?

Thanks everyone

 

[Tuttles Revenge]

Just found my 10 foot pole. Open loop systems are gross. Water sits in those line and becomes stagnate then at some point gets mixed into the cold water and distributed around to drink..

 

[Sponsor]

 

[Ryan Edwards]

Just found my 10 foot pole. Open loop systems are gross. Water sits in those line and becomes stagnate then at some point gets mixed into the cold water and distributed around to drink..

The 3 100' loops will only contain abut 4 gallons of water. People will be living upstairs so the system should easily have new water flowing through it daily.

Maybe I should add a one-way valve or backflow preventer to the cold inlet.

 

[Ryan Edwards]

I've learned that the default temperature is 120 not 140 and that the pump and expansion tank should be on the hot side.
Does anyone else here have any input?