Zone valves in an open system

palladin · November 2020

A beginner looking for help on an open residential system. A cabin in western NC. Building an open system utilizing a Takagi 199000 btu on demand as heater for heat and house hot water. Have 2 levels- lower is walk out basement( very well insulated) 2” polyiso foam under slab and on block walls and 6” f’gls in stud walls. 1/2” pex under slab about 2” down. 1zone has 3 loops of 225 to 250’ each, 1 of 2 loops 245’, and 1 zone of 265’. The upper level is 6” logs( white pine) for exterior walls. Subfloor is 3/4” Osborn’s with 1/2” engineered hardwood over. Windows are aluminum clad 1/2” insulated. There is 1 1/2” of airspace between the 1/2” pex and the 2” foil faced polyiso below it. There are 1 zone of 4 loops about 250’ each and 2 zones of 240’each. Each floor level is about 1250 square feet.
What I was hoping to do was plumb this open system using zone valves and a variable speed circulator for each level. All the suppliers I talk to when trying to buy pumps, mixing valves, and zone actuators try to sell e a pump for each zone. I understand how the normal open system needs a zone open in order to get make up water to flow to house fixtures and make up water into the floor system.
My big question- is there a way to feed hot h2o to fixtures and make up h2o without a flooring zone open. Any help would be appreciated. Having a hard time getting my 77 year old brain around this one. Thanks Palladin

Jamie Hall · November 2020

Two questions. Why, oh why, are you using a water heater as a boiler? They're made for completely different applications. It's a little like using a Peterbilt to go out for coffee at Dunkin' -- or like using a Honda to haul that 53 foot box trailer.

And second, why, oh why, are you looking at an open system? They are among the worst possible arrangements for breeding nasties in the water -- particularly radiant floors, which are, of necessity, held at just about perfect temperatures to encourage bacterial growth.

You will be much happier with using the water heater solely for your domestic hot water, and using a properly sized (and thus more economical to run) small LP boiler to run the radiant floor.

Please reconsider.

SuperTech · November 2020

Please don't install an open system buy a properly sized combi boiler.

Why does everyone who asks about a Takagi always trying to use it in place of a boiler on an open system? Who is pushing this bad idea?

EBEBRATT-Ed · November 2020

Or at the very least make the heat a closed loop by using a heat exchanger off the Takagi

Ironman · November 2020

Using domestic water for radiant heating is a very bad idea and has been outlawed in most places. You’d be creating a Legionella breeding machine which the elderly and people with weakened immune systems are very susceptible to dying from.

Also, tankless water heaters are not designed, controlled or approved for space heating. Some internet peddlers push these playing upon people’s desire to save money, but they only have their own interests at heart.

Think about it: if a tankless water heater could replace a boiler, there would be no need to make boilers. Boilers are more expensive because they contain the components necessary for hydronic heating and they’re designed for that. However, they’re several mod/con boilers that aren’t that much higher in price that could do the job including combi boilers that would safely provide domestic also.

Zone valves in an open system

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