What to replace Vertex with for DHW and small radiant system?

Albany Chris

My NG Vertex has failed after 15 years. I bought it for its high efficiency and the big rebate at the time, though it is overkill for our needs. In addition to DHW we use it for a floor warming system in the master bath. (130sf w/uponor plates with one loop of 1/2" pex. Its an open system which is flushed before each season). Also have a on-demand recirc with dedicated return line. 4BR house with normal hot water use.

I'm seeing conflicting info about using a tankless WH (like a Navian with recirc) and many of you don't like it in other discussions, though HotRod seems somewhat OK with it :) . What would you guys suggest? Vertex seems like overkill and prices are much higher now. Is there another NG tank model that would be a good fit? Separate systems seems like overkill for such a small radiant system? I might upgrade to add a heat exchanger and close the system if that matters.

Thanks Everyone.

edit, wording

hot_rod

https://forum.heatinghelp.com/discussion/201819/what-to-replace-vertex-with-for-dhw-and-small-radiant-system

Not me okaying a tankless WH as a boiler :) I think @Kaos has suggested them for some systems.

A boiler or combi are my suggestions.

GroundUp

The problem with any high efficiency boiler/WH/combi is that none of them will ever turn down far enough for only 130SF of radiant. There are a few "correct" options here, but all of them are going to be costly if you are dead set on high efficiency equipment.

1. Combi w/ buffer tank
2. Boiler w/ reverse indirect
3. Tankless WH w/ storage tank and HX

If it were mine, I'd probably just convert the radiant to a standalone closed loop system on its own 6 gallon electric WH and have a separate WH for DHW only. Possibly a regular old power vent WH tank with a bronze circ through a HX, also making the radiant a closed loop. The Vertex variety of HE tanks really doesn't save you a whole lot in the long run, as far as I'm concerned.

Kaos

Tankless units still have a minum output. The problem is your floor heat is too low of a load for it. No matter the tankless unit, it will cycle too much.

The way you can make it work is with a small buffer tank after the tankless. The floor heat is tapped taken off the tank and the aqua stat on the tank drives the recirc pump. You don't need a separate aquastat, you can use the power leads on the tank directly as a switch.

Beside fixing the cycling issue, this has the added benefit of eliminating star delays and cold water sandwich.

I think the simplest is to go for a regular power vented tank tough. You can put the floor heat in series with the recirc, in the winter run the recirc continually during the day. In the summer run it on a demand or timer switch which will also eliminate your stagnation issues. Let it sit and flushing it is not the best idea.

hot_rod

I have used the Butler Solar Wand for a few micro radiant systems. Like a single bathroom.

You drop this double walled heat exchanger tube into any HW tank to pull some heat out.