I doubt you want to prioritize snowmelt over space heat.

check valve in boiler loop would be an unnecessary choice. boiler pump should be running anyway whenever there is a demand.

why use a 150k heat exchanger? that's more heat than your boiler can even provide... is there some water temperature management/special sizing going on here?

wouldn't bother moving garage unless you're planning to maintain VERY low garage temps.

this is not hydraulically separated. closely spaced tees off of boiler circuit for the zones supply then return within a few pipe diameters of each other.

can't imagine you need a 26-99 but then without flow requirements/heatload/design who can say. if you do use it, you want pressure bypass valves to save wear and tear on the pump and zone valves. with a 60k calculated load on the house I would presume that a 15-55 alpha would do it, for about 1/8 the pumping energy. but I'm guessing blind.

also I missed your last replies sorry. your contractor has no idea what he's doing. he's got massively oversized pumps on pipes that are too small hooked up to a highly restrictive heat exchanger. in short, he's incompetent to design a piping system.

I don't understand the blue line under the orange line in your current system doc. water can't return that way, there is no pump making that happen... right?

Thank you for your responses. They are VERY much appreciated.

The snow melt system would only be used very rarely and I am mindful that a 122,904 btu boiler is really too small for the 1600 sq ft area of drive/sidewalk to be melted (even at 80btu/ft I'd need 128,000 btu/hr as an absolute minimum, I think). As such, and understanding that I have an alternate forced air heating solution for the house, I would (actually) be okay with prioritizing snow melt for the few times a year it is run. That said, I am wondering if I wouldn't be better off just having a dedicated and larger boiler for that application so that it works when I want it to. Water temp would be limited to 125 degrees to avoid stressing the concrete (basically, as the boiler temp is fixed on the boiler, I have to run at the upper end of the allowable temps for the inside radiant to get acceptable warmth to the outside slab, no?).

Assuming we continue to use this boiler for the snow melt, what are your thoughts on the new sketch I came up with (assuming that the boiler loop was made larger to avoid the hydraulic separation issue present in the current sketch? What is the separation distance required?

Re: the heat exchanger, assuming that you wanted to transfer up to 100% of the available heat from the boiler, wouldn't a slightly larger heat exchanger make sense (or is there a reason to go smaller)? Does its placement in the boiler loop make sense? The alternative would be an additional pump to force water through the heat exchanger when the snow melt zone calls to avoid a constant boiler loop restriction.

The blue line in the current system drawing was placed prior to the creation of the boiler loop now in place. That blue line was added by the contractor at my statement that his design didn't allow the possibility of the snow melt zone calling and getting any boiler heat since no hot water would traverse the 'boiler side' of the exchanger. With the boiler loop now in place, your point is well made - the snow melt zone does not have the possibility of working, something that I hadn't considered until note. Thanks for pointing that out!

At issue with the garage is that the loops come to a manifold within the garage. If someone leaves the garage door open all day when it's 0 degrees out, the manifold is exposed and nothing prevents the fluid in the manifold from freezing.

The 26-99 pumps were said to be required since the boiler panel is on the basement level of the home, the second story manifolds are 22' higher, and the 3/4" supply and return lines to those manifolds are 80 line feet. I argued that the head calculation should be made irrespective of building height, but the contractor persisted. I hadn't done near the level of research that I now have under my belt and allowed myself to be swayed. The result is over-sized pumps. If I am going to rip all of this off the wall and start over, I'd do the pump sizing calculation as part of it - I just need to dig out my head calcs from the engineer. The AutoAdapt function of the Alpha pumps is amazing.

I also never understood why I need zone valves in my current system when the system on the wall is zone by pump and the pumps have integrated check valves.

Wouldn't I want the check valve in the boiler loop to positively prevent mixed water from entering a zone? The opposing argument would be that since the 15-58 boiler loop pump does 17gpm and since the entire system flow is less than 17 gpm, that the check valve isn't necessary since only direct boiler water will ever be seen.

I would think that the only reason to even have a boiler loop in my application given the flow controlled boiler is for the possibility of the snow melt zone to work.

Please let me know your thoughts. I am a neophyte at this to say the least.

you do not want a check valve. hydraulic separation is specifically to decouple flow from one loop from flow in another. the 15-58 should pump in a loop and your zone pump should pump in a loop without either knowing the other is there. that means you could recirculate some water from return to supply if your zone flow is higher than your boiler flow. that is what it is... no big deal. in that case you're still putting all the boiler BTUs into your zone stream and it will elevate in temperature over a bit longer timeframe.

to hydraulically separate properly, you want the zone supply and return takeoffs WITHIN about six pipe diameters on center, with something like 8 pipe diameters of straight on either side of the tees. though if the boiler circuit piping to be generously sized, you can fudge the rules a bit: the goal is to make the pressure drop between the two tees practically zero.

You need a boiler loop to get the highly restrictive heat exchanger out of the hydraulic loop with your zones, so your zones can circulate properly.

you need about 190kBTU to snowmelt an area that large successfully. snowmelt control has many options. I think you're about to go heat source shopping if you want a functional snowmelt of that size... and judging by the rest of this system I would be very sure the loops and manifold feeds and such are sized properly before buying a heat source to hook up to a fundamentally flawed install (potentially).

I don't usually harp on the design thing as much as some others (mainly because it's self serving, me being a designer and all) but it sounds like you really need it here. probably from the ground up with load calcs, survey of your installed loops, and a from scratch piping diagram.

I do, usually harp on design and serve others by helping them avoid the total disaster you have here. Get a competent hydronic designer and pay him to save money and ultimately get what you are paying and paying for, without the aggravation.
I know; just one more question...

Were it so easy.

I have a bunch of what I already need here - engineered load calcs by level and zone, AutoCad depiction of loop placement, and Rehau balancing manifolds. With some loop flow adjusting that the contractor couldn't be bothered to do, I now have a system that is far from perfect but at least SOMEWHAT functional - at least now with the addition of the 1" line and boiler loop I don't have any zone starving for flow (even if my boiler can never see its true and full potential given the inadequate boiler loop sizing (am I right about that, btw?). Mistakes made were in boiler selection and contractor selection for the boiler panel. The contractor selection mistake resulted in a pump sizing mistake, a zone by pump AND valve setup that is just unnecessary and bizarre, undersized piping just pretty well everywhere on the boiler panel, and a host of other issues you folks know about better than I. Am I correct in that my proposed design is a vast jump in the right direction from what I have now? I really appreciate the help here, guys. Any designers in the Des Moines, Iowa area you folks can recommend (or is a local designer even necessary so long as the 'plumber' follows the resultant design?)?

Actually, another question...with the current system set up with oversized pumps and all... Couldn't I just replace my 26-99 pumps with 15-55 Alpha's if the head calcs work out? It would seem that my #1 issue right this second is that I am wasting electricity on my pumps. A close second might be whatever wear/tear may be occurring on my manifolds by way too much water hitting those valves. I am getting flow to all zones now, meaning that the system *is* officially now working, now that I regulated what the basement loops are seeing for flow. It would seem that while the design is FAR from ideal, it is actually now functional. Anything wrong with this approach? I understand that my snow melt setup cannot work as things are designed right now without another zone calling.

I have no idea if the flow you can get through the heat source in your current configuration is adequate for your home or not. so it's hard to say. and unless you do the hydraulic separation thing, you need to be sure to include the heat source in your head calcs.