Let's say you are an designer or installer of HR systems, and an architect or home owner asks you how much room do you need as a dedicated mechanical area.

Assume a northern climate, zone 5 or 6, slab on grade 2,300 SF including a 500 SF loft, lots of south facing windows with overhang, energy efficient design above code minimums, so on and so forth.

Assuming natural gas, wall hung instant on serving as both boiler and domestic hot water, how much wall and floor space would you ask for?

What sort of area increases for a boiler and tank system?

Looking at:
[quote] A hydronic radiant floor heating system consists of a controller, boiler, pumps, distribution plumbing, manifold stations (often fitted with solenoid shutoff valves, flow rate balance valves and supply/return water temperature and flow rate gauges), and PEX tube placed within the floor of your building to successfully transform it into an efficient heat emitter. [/quote]

I assume just like with an electrical panel needing 42" of clear space in front of it so a service guy can get in there and do his thing, there are requirement here as well.

From what I see on Youtube it looks like it can all fit on about (4) four feet of wall space. 

People seem to be mounting on plywood, so I'm not even seeing non-combustible construction.  On the job sites I've been on I have only seen the row/riser of PEX tubing rising up before the pour, did not get to see the finished installation.

Well, my 2400 sf single-level house is a passive solar design with HR floor heating. It has a NextGen-4 (4 kW or 13,652 Btu/h) boiler HR appliance, HRV, septic system alarm, central vacuum system, electric tankless water heater and 200A circuit breaker panel which are all contained in a corner utility room that is 8’x4’ and has a door going to a sunroom (i.e., a screened porch that can be heated with electric radiant heat when desired) and a door going to bathroom allowing it to also act as a mud room. The HR single 12 circuit manifold is located near the center of house in the office wall to optimize the circuit layout. The kitchen range exhaust duct also passes through this utility room before exiting the house. The house also has another 200 A circuit breaker and a second tankless water heater on the other side of house in the laundry room to service the master bedroom suite.

Thanks, sounds like about double the wall space of what I was thinking (but I would have added a couple of feet for the elec panel).

If you can pass through this space without incident, then assuming 36" clear walking space that none of the equipment protrudes more than 12" off the wall (36"+12"=48").

Yes, nothing protrudes more than 6" from the wall. The HRV hangs from the 10' high ceiling with adequate head clearance. A propane boiler with the required HR components also mounted on wall will require more space than the electric NextGen HR appliance.

We also have hydro, solar and diesel generator alternative power, but all that electrical and mechanical infrastructure is in our detached garage/shop/guest quarters building so all the alternative power and grid power can be isolated and fed to the entire homestead from this single location. I only mention this should you also have a need to host alternative power infrastructure too.