*
I am installing a Heat-Link brand radiant floor heating system. The floor water will be heated from the house’s domestic hot water supply. The manufacturer recommends the use of a heat exchanger to keep the floor water separate from the domestic hot water. This set-up requires two circulation pumps, one on the domestic side to keep hot water flowing through the heat exchanger, another on the floor loop side, to push floor water through the heat exchanger and then on to the loops. Both pumps come on simultaneously.
Have you guys ever installed a system with a “isolating heat exchanger”? Other radiant systems I’ve seen either used a dedicated boiler, or circulated domestic water through the floor loops – this same water would eventually end up looping back to the domestic water heater, and used for bathing, cooking, etc.
Needless to say, Heat-Link’s recommended configuration implies the outlay of some serious cash. Thanks for your help.
Replies
*
My inspector required me to do that. Quoted a section of code to the effect that heating system water must be isolated from potable water. Typically this would be done through a check valve and pressure regulator to keep the hydronics topped off but at a lower pressure and without any backflow.
My argument for skipping the HX is that all the hydronic components (PEX tubing, copper pipe, bronze pumps) are all food grade materials. And I am certainly not going to add gycol to the system, knowing that it is intermingled with potable.
The added costs for the HX approach include the additional pump ($100), the HX ($125), and some relays if you want the HWH pump to only come only one a zone wants heat (versus leaving it on all the time). Plus the labor to install them and do the complicated piping. And an expansion tank ($50), because the hydronic side is now a closed loop. In the combined system, expansion takes place by going back out a little bit through your incoming water service line. You should plan on a tempering valve (like 85F to at least 120F, $80) in either set-up. And I would also recommend another tempering valve going out to the potable hot water piping. This allows you to crank the HWH setting if needed and corrects the damnably large hysterisis of new "energy-efficient" HWH's.
If your inspector is cool with it, I'd definitely do it without a HX, as you had planned. Also be aware that some natural gas companies get all paternalistic and think they can dictate the plumbing inside your house. Sometimes it is easier to get the gas connected with something simple (cooktop or clothes dryer) connected. And then do the interesting plumbing after they go away. Happy in the North Woods with warm feet, -David
*Pierre, Here's an article that has some additional info re: setups with and without heat exchangers.Regards, Mongo
*Yeah... just wait until you read up on legionaires disease. Research what the ideal conditions are for the bad stuff to grow. Then compare that to the conditions in your system. Then research how it gets transmitted. (Airborne through fine mist or droplets is the ideal way) Does that sound like your shower? Do you breathe while showering? (I don't want to know about anything else you do in there though!)Make your decision based on the facts combined with common sense combined with your level of willingness to take known risks...Sorry, David, I thoroughly disagree with you on this one. But your answer showed you are familiar with the subject. Exactly what DON'T you know? And that is a sincere compliment.PS. Anyone can argue all you want. Go ahead. If you want to install systems like this go ahead. I will not risk it because of what I have learned.PPS. I am not against using a WH for space heating. Lots of disagreement there... but... look at the risks and costs... and I will most likely do it on my own house.
*WHW: You raise the concern about Legionaires disease in a thoughtful way. My review of the disease has only dealt with open-air situations (swamp coolers, ductwork below the dew point, etc.) You argue (and have in the past?) that it can develop in enclosed piping systems.My combined system has a total of 13 gallons in it. A typical house with potable piping only, might have 4 to 6 gallons, depending on how close the plumbing fixtures are to each other. Adding the HWH, I have 63 gallons in the house versus other houses at 55 gallons. So the water stays in my plumbing a bit longer, but not much.If I go to New Zealand for 6 weeks and return to a normal house, should I flush the plumbing with a disinfectant solution? I don't think anyone does. And my water is never idle that long, by a long shot (except if I go to NZ).Now, I do have dead legs, like the hot and cold lines (both!) to the hose bibs. But lots of people don't use their hose bibs for 6 months and therefore have stagnent water for a long time. A bit of it would slowly intermingle with the rest of the potable water and a long-stagnent slug would come out each spring with the first use.I don't want to be saying, "Everyone does it (to some extent) so it must be okay." Smoking, overeating, and too much sun exposure all disprove that logic. But that various forms of stagnation exist in everyone's house and Legionaire's remains at a low incidence rate suggest to me that other important factors are at play when it does arise.I get chlorinated city water and I would certainly see more possibility for the introduction, development, and continuation of a problem with an un-treated private well. Do you feel that that is a factor in the risk equation?Stuff I don't know? Jeez, where to start? I'm crap at complicated roof framing. I wouldn't fly a multi-engine airplane. Nor almost any type of surgery. Many aspects of "high-culture" - art history, classical music, biblical scholarship, etc. Harvesting warm-blooded critters (the freezer's full of slamon and halibut). Foreign langauges. The list goes on. -David
*You know what? I really can't argue with anything you said. The only thing I will argue on this subject is that it is not smart for me as a contractor to do it this way for liablity reasons. In this day and age I am sure you will agree with me.Here is another point I really don't know what to think about. I have seen a number of these systems. They have always been installed by the scum of the plumbing profession. I don't say that because of these systems but based on the rest of their work. (Venting boilers into the garage, plugging leaking relief valves, installing boilers on combustible surface without required plates -almost burned the house down-, etc) I am sure good plumbers install these systems too, but I haven't seen any. Any thoughts? To me there seems to be a connection... but I don't know. It is actually cheaper in most cases to install the second water heater than do the heat exchanger, etc.
*One more thing... I do not have a lot of answers on Legionaire's. There is so much conflicting data out there it is hard to say what is true and what isn't. Lot's of paranoia perhaps including yours truly.The latest thing is a scientist saying that most Legionaire's is not that at all but a poisoness gas?????Lot's of controversy.
*I could toss out a few theories about bottom feeders and simple systems. If you only understand a few plumbing components, then you lean towards using only those. I think boilers and complicated control schemes are scarier to some newbies than a HWH (everyone has one. Install in it an afternoon, etc.).My sense of many plumbers is that as they gain experience, they have call-backs and have to fix other contractors bad designs. So they start to pro-activitely (and perhaps unconsciously) install more general-purpose system (oversized boilers, flexible controls, lots of zones).It takes both skill and science to utilize a simple system when it is appropriate. To match areas of similar heat loss characteristics and put then in the same zone. To view the house as a system (insulation, air leakage, solar gain, occupancy patterns) and balance a system (mostly) during specification and installation rather than after the fact.Sometimes I spend hours watching a piece of equipment and its response times, cycling, etc. And run around with a IR thermometer to track small temperature differences, heat losses and such. A plumber that has that kind of interest in his craft will hit the mark much more often. And will find ways to accomplish the goal with simpler components.So maybe some sub-standard plumbers go this route (for dumb simplicity's sake) as you have seen. And a few excellent plumbers would use them when appropriate. But all those run-of-the-mill plumbers out there are installing run-of-the-mill heating systems. Not pushing the envelope in either direction (neither stupidity nor clever, elegant simplicity). Just installing what the supply houses and manufacturers are presenting in their seminars.
*Wow! The concepts you speak of are the very ones I have been studying and applying a lot lately. I even went back on a system with the fancies and applied my new knowledge. Cost me a couple days and a couple hundred bucks. But I know they now have a better system without losing any performance. He offered to pay. I declined. Sure wish I could sit down with you for a cup of coffee a couple times a month. Coming to CO soon?About boiler sizing. I sized one 25% under the called for size. Near design temp it ran about 40% of the time. Makes you wonder...
*Thanks to all for coming through with lots of useful and relevant info/references. I will definitely keep the domestic and floor waters separate, by dedicating a hot water heater to each of the tasks.No heat exchanger, no serial or parallel plumbing between the heaters either. A simple back flow prevention valve on the floor water heater's inlet side. Pierre
*And an expansion tank, please. That P&T blow-off valve is for emergency malfunctions, not routine use.
*Many multi-family and apartment complexes here doing combined systems with no HX.-RobP.S. - My own office I am in right now has a loop of baseboard off my water heater.