Open loop hyrdronic slab radiant heat — current opinions?
One can read online for hours and hours back 10 years on the topic of whether an ‘open loop’ hydronic radiant floor heating system, which uses the domestic water, and heater, for floor/space heating.
FHB #201 March ’09’s article outlined the ‘sharp divide’ over potential health risks–legionella bacteria–vs. the simplicity, efficiency and safety of an open system.
So what’s the current opinion?
My area allows open systems by code–inspector has no problem with it.
I’m building a shop with living space above–600sf of slab with 3 <300′ loops. Upstairs has bath with shower.
Tiny utility closet for mechanicals.
Should I go the extra $$ and and get a combi boiler or another pump and heat exchanger to separate the less than 900′ of tubing volume that could breed legionella bact?
Replies
waters
I have this set up.
1-boiler, pumps for each zone (now-probably would have used zone valves for separation), water tank heated by the one boiler.
A time tested system I am happy with.
Do not get a cheap tank, went through one in 12 yrs, now have a "lifetime" Gold from Amitrol.
I'll add some food for thought ... but not much opinion, really. As I always say there's a time and place for just about everything.
Open loop is higher pressure in your radiant piping, right?
Legionella is not a problem, I don't think. Other health issues from stagnant water may potentially be. Legionella, I think is common only under pretty specific conditions and temperatures ... associated with misted water and warm temps (but I'm not expert). Don't you have to have a way to flush the system seasonally? Maybe that is as simple as directing cold water supply through the slab during the summer ... which can be beneficial (or maybe not if it is humid in your area in the summer). Allowing the water to just sit there for an entire season, I think is inherently a problem. That is why codes require a back flow preventer between irrigation and potable water uses. So it seems like you'd want a way to keep it flushed out in the summer ... not sure how that is done, but it shouldn't be difficult.
A friend of mine did the open loop thing. I did the combi boiler/water heater closed loop condition. Done right, either works.
Others will chime in w/ more.
Here's how Radiantec suggests an open-direct system:
http://www.radiantec.com/systems-sources/open-system.php
Looks like they've been at the center of this argument for a long time.
Fresh new water enters the floor from the cold supply every time hot water is drawn from the tank, for domestic use in the building so the floor system is constantly being flushed. There's a one-way valve just before the cold input in the heating loop.
As for pressure, it looks like the entire system is at street pressure, which is one issue in going this way: many of the manifold setups for closed radiant floor are not listed for potable water, or aren't rated for higher pressures.
Seems outrageously simple.
Here's how Radiantec suggests an open-direct system:
http://www.radiantec.com/systems-sources/open-system.php
Looks like they've been at the center of this argument for a long time.
Fresh new water enters the floor from the cold supply every time hot water is drawn from the tank, for domestic use in the building so the floor system is constantly being flushed. There's a one-way valve just before the cold input in the heating loop.
As for pressure, it looks like the entire system is at street pressure, which is one issue in going this way: many of the manifold setups for closed radiant floor are not listed for potable water, or aren't rated for higher pressures.
Seems outrageously simple.
I've had and have radiant heat systems in my buildings/homes. I think that a separate hot water heater is not all that much extra money and it allows the two systems to be apart. I've no scientific rationale for this other than this... it's just sort of how I've always done it and it works. Perhaps I'm an old dog to whom one cannot teach a new trick... but I don't feel like that.
You obviously have doubts about an open system. Why take a chance when another hot water heater will deliver more security?
Not so much doubt as interest. I like a well-formed opinion before embarking. Perhaps a better way will emerge.
My biggest obstacle to separate systems is space. I have a tiny utility closet for the mechanicals.
Perhaps one water heater and a heat exchanger?