.

Open type systems can be prone to that . . and often can require different materials as heating water can come in contact with domestic water. They must be compatable with drinking water for sanitation purposes.

Easiest way to avoid any such issues is do a closed system. It connects to domestic water supply in only ONE place -> through a backflow preventing valve => all the issues of stagnation / domestic supply go away . . . and in my mind it only makes sense to keep them separate anyway . . .

Bob

An open system is the perfect breeding ground for the bacteria that cause Legionnaires Disease. You may never get it, but why risk it?
What are the benefits of an open system? I cant think of any (not an expert, though) and cant imagine that they would outweigh the risk of serious health issues.

Jeff

If an open system is plumbed properly the water will only be as stagnant as all of the other domestic hot water in the potable system, rendering it as safe as safe can get. To do this, the incomong water service must first circulate through the radiant tubing before getting to the hot water source. Every time domestic hot water is called for (opening of a hot faucet), the entire radiant heating system gets flushed out. The water will only be as stagnant as every other hot water pipe in the system (or even less so if a faucet location is not used very often). A back-flow valve must be used just upstream of where the source water enters so that the incoming water flows forward. One might argue that the incoming water cools the system - in terms of the whole system though, there is only a temporary transfer of heat from the floor back to the heat source, but it really shouldn't be thought of as cooling, except during the non-heating season. The entire system retains pretty much the the same amount of heat (losses would be only with the transfer through the conduits). The benefit of open direct system is that it is more efficent because there is no heat exchanger. The floor cooling in summer is also a nice benefit. Two things to check: must use all potable equipment including pumps, expansion tanks, everything; and, check with your local code enforcement folks - some places don't allow open direct. The typical reason that they don't allow it is fear that non-potable equipment might be installed during repair or other maintenance work (that would be a real concern - an open direct system should be clearly identified as such so that anyone working on it is aware). I'm a fan of open direct and I think the health threat is a non-issue as long as the system is done right.

.

" The benefit of open direct system is that it is more efficent because there is no heat exchanger."

Not sure if I understand / agree with this statement => I've got a closed system . . there are NO heat exchangers anywhere in the entire system . . . . dedicated boiler pumps directly to the zones / tubing . . that's it.

I'll also point out that it's simpler plumbing / two independent systems: domestic hot water / heating system => one can be worked on without shutting both down . . . .

Bob

Bob,
if you heat your water with an indirect tank, you need a heat exchanger. I assume this is what early1 meant.

Early1,
I still donÂt see a benefit to open direct. Yes, you donÂt need a heat exchanger, but now you need all stainless pumps, valves, etc. If those costs are not a wash, it must be close. Where is the efficiency savings for not having a heat exchanger? With a heat exchanger, all heat lost in one goes to heating the water. The fact that some places donÂt allow open systems should be enough of a red flag that it is a bad idea. And it is now a more complex system requiring special care for maintenance forever.
Since I donÂt see any real benefits to an open system, why would I put it in?
The risks of Legionnaires is very, very small, but why do something that is out of the norm, may not be allowed in your town and has no benefit in order to get a more complicated system that increases the risk?

Jeff

The upcharge for potable equipment is small. Valves are just normal valves used for the domestic water system. I don't agree that all heat lost goes to the water. Nothing like a cool floor in the summer. Sorry, not much time to discuss right now - I'll check in later - early.

While I do agree that cool floors in the summer would be "cool", and it has been done to actually cool the house, great care must be taken to manage the humidity when using radiant cooling so that condensation does not appear on the floors. I doubt that would happen too much with this type of open system, but if you have 40-50 degree water running through the pipes while filling hot tubs, doing laundry, even watering the lawn or filling kiddie pools, it could be cause for concern.
Anxious to hear more from you when you have a chance.

Jeff

Just a few more thoughts in response:

Under conditions that would cause the condensation, floor cooling would not be able to keep up alone. An A/C system would be needed. Typically floor cooling supplements rather than replaces A/C. The floor cooling only occurs when domestic hot water is called for. That activates the supply water to circulate through the floor tubing. The highest efficiency of Open Direct is achieved when a high efficieny domestic hot water heater (95%) is used in lieu of a boiler. Heat exchangers work at 75% so efficiency is reduced. The open direct system is not very complicated - its beauty is actually in its simplicity. The heat exchanger of the closed system adds complexity. Another nice thing about open direct is that it can be supplemented with solar - preheated incoming water can be stored and fed to the dometic hot water heater for use both with heat and domestic water - most environmentally friendly system I can think of. Jurisdictions and codes are slowly coming around to recognize advantage of open direct, but as with many new ideas, change is slow. don't get me wrong - I don't sell or benefit form open direct except for my own system. I orignally posted here because the original question was about safety which I wanted to address directly.

Hello,
IMO, Open Direct is just a name. Most commercial buildings over 1 story have circulating pumps for hot water. This is basically the same thing. They do not need stainless piping. The only difference between hot water circulation and cold water circulation, is the hot water pump is bronze instead of iron.

Using Solar to preheat water will always reduce energy requirements. The real trick is to use solar to cool also. Then I am very interested. I live in a hot climate, where cooling is needed more than heat. Very few companies have sold standarized equipment to cool from solar heat. It has been done thousands of times, in commercial and residential systems, for over 100 years. Why not now.

I think it's more than a name. Open direct means that the same water that is used for domestic use is also used to circulate through the heating system. Shower water is one in the same as heating water. Water used in the dishwasher has circulated through the heating system. The hot water tank is used to heat and is part of the heating loop. Way different than a closed system where water for heating never mixes with the potable water. Hence the need to use pumps for potable water.

Not sure how solar cooling would work - explain?

Responding to rcjmr's comment on needing to shut down entire system to service, unless it's the actual heat source being serviced, valve isolation works well to shut off parts of the system. Regarding the comment on closed system with 2 sources being separate, that's true, but I was assuming that the radiant water was using the domestic hot water heater - apples to apples when comparing with the open direct.

I have a quick question on utilizing the cold water for cooling. I assume to cause this during the summer you have a diverter valve on the cold water feed to the hot water heater causing it to flow through the the pex. When the cold water hits my zoned manifold what causes my pumps to fire causing the cirulation? Or do I cut a second diverter valve in to my zones after the pumps?