Hydronic System from Scratch

panndder

I have an older home in the upper Midwest and I'm looking to completely replace my existing boiler and domestic hot water with something more compact and efficient as a part of a basement finishing. I have a separate high-velocity system in my upstairs knee walls, so my focus here is solely on heat. At a high level I have a 750 square foot basement plus about 800 square feet on the main level and another 330 or so upstairs.

My high level plan is some sort of ~95% ~85k btu boiler (Lochinvar Knight is my default assumption for the time being) that heats oxygen-free pex in the slab and under the main level subflooring plus an indirect tank. I'm also going to allow for the possibility of a basement towel warmer and/or upstairs radiator in the future. I hired forum member Steve Minnich to do a load calculation an draw me a basic boiler configuration and gave me a great diagram for this based on the demands I gave him. But, as I've been learning more about these systems my thinking has evolved a bit and he graciously welcomed me offering it up to the forum for input. I'm hoping to discuss the merits of pumps vs valves, traditional vs variable speed pumps, 4in1 separators versus separate components, DHW expansion tanks, condensate neutralization with ABS drain pipes, and lots of other fun things given that I'll have all summer to design, install, and commission this system.

I've had a million different ideas and questions running through my mind as I've read about boilers and the like the past month or so I'm hoping to use this thread to bounce them off others and hopefully it'll end up being useful for others, too. I'm looking to keep costs reasonable where I can but I'm not on a fixed budget for this project. The biggest desire is a comfortable house that's efficient, quiet, and reliable. The secondary desire is saving on space, so I'm even toying with some things like hanging a horizontally-oriented indirect tank.

I'm soon going to demo and replace my basement slab, which takes me to my first big decision point from a heating perspective: the pex configuration. I'm planning on stapling oxygen-barrier pex to 2" foam and am looking for even distribution. It'll be a ~4" slab and Steve's calculations call for about 11,300 BTU.

I'm also intrigued by the idea of adding a towel rack down the line and thus allowing (or necessitating, depending on your perspective) us to keep the bathroom a degree or three warmer than the rest of the basement. I have a few questions lingering around this, primarily regarding as to whether that makes sense. If I have my whole slab set to one temperature and a bathroom with basic (interior, including ceiling) insulation set a degree or three warmer is it practical that they'll work in harmony? Should I be making a dedicated in slab zone for the bathroom? It looks like a lot of them are rated in the 2000 BTU range so I'm curious if would overwhelm the slab's thermostat pretty quickly on milder days. I'm not wedded to this idea, but I'm intrigued by the idea of having a warming rack connected to the boiler. Finally, if I do this should the run be insulated from the rest of the slab, and what's the best practice for doing so?

And more generally:
3/8" vs 1/2" pex?
3 vs 4 circuit manifold?
Is Bluefin okay or is it so cheap for a reason?
Anything special to consider for selecting a manifold or pressurizing the system for pour? I plan to get some elbows to run the pex through where it'll enter the concrete, but are there any other nice touch things like that to consider?

Thanks in advance!

hot_rod

10 installers may give you 10 different ideas of an "ideal system" Find the line between too little and too much zoning. Component brands and types are also a very personal preference on the part of an installer or designer.

Key component is having an accurate load calculation and design, from there the sky is the limit for customization.

panndder

Thanks to both of you.

Will I be happy with Bluefin pex or would I be wise to spend more?

GroundUp

For the slab, Bluefin is fine. Under the subfloor, it'll be noisy as the EVOH layer is on the outside.