Radiant heat and domestic water on same system?

Users who are viewing this thread

Chris Haas

New Member
Messages
4
Reaction score
0
Points
1
Location
Pennsylvania
Hello all. I'm brand new to the site, but I'm nearly at my wit's end.

Bottom line up front: I need to learn how a combined radiant heat system and domestic hot water system should be properly plumbed. I apologize for this very lengthy post, but PLEASE read it all before replying. A lot of work has been done (at a price of over $4,000 so far), seemingly only to get me back where I started.

Facts:
1) The home, built in 2005 (including the radiant heat system), is fed by well water.
2) Hot water for the radiant floor heat and for domestic use is supplied by the same GE 80-gallon electric water heater. This water heater was installed in May 2015 - just 18 months before I bought the home.
3) To the best of my knowledge, the water heater is NOT equipped with a mixer valve, and the home is not equipped with a crossover valve.
4) I have yet to find anyone in my new area who knows/understands my home’s system. All are intimately familiar with boilers.

Background: I purchased my current home three months ago (in November 2016). I chose the home for several reasons, not the least of which was the radiant heat. I admit I knew very little about such systems, but I was impressed with what I read about them online. It has been a nightmare ever since.

Shortly after moving in, I noticed the water we were using was brown with a great deal of sediment – mostly when using hot water. Being a basic DIYer (my expertise is Navy fighter jets and fixing my own cars), I set about to flush my hot water and well water pressure tanks. The drain on the hot water heater tank clogged quickly. I successfully freed up the clog using a bicycle tire pump. It worked better than I thought possible, but it’s a process best shared on a separate thread upon request. Discharge from the hot water tank was unbelievable. Large scaly deposits, black sludge, etc. Eventually, after draining countless gallons, the water coming out became pale brown. At this point I shifted attention to the pressure tank for my well water. Surprisingly, this water came out crystal clear. So I went back to the hot water heater and drained many more gallons, although never achieving crystal clear water.

Now to the well water itself. Out of the blue one day, I observed a significant drop in water pressure. I narrowed it down to a clogged sediment cartridge - the only source of filtration at the time. I recalled the seller left us a replacement sub-micron cartridge. I changed the filter and restored pressure to the house. Problem solved – temporarily. A little more than two days later, the system pressure was low again. Thinking the problem was the sub-micron filter, I purchased and installed a standard 30-micron filter. Problem solved again – this time for about 10 days before clogging. Time to call a pro.

After finding a local water quality expert I could trust (the first two were remarkably bad), I had the standard sediment filter removed and a water softener system (plus a UV light, separate subject) installed in its place. The installer also noted the pressure switch for my well was set too low, which he adjusted. The difference was remarkable. I suddenly was able to take comfortable showers, and the water from my faucets was crustal clear. However, the installer did warn me I still had an issue with high total dissolved solids (TDS). Knowing I was a DIYer, he suggested I install my own reverse osmosis (RO) system under the sink for drinking, cooking and making ice.

I know – we’re supposed to talking about radiant heat. Just stick with me here. I warned you this was a long post, but I felt all of the background was important. It will all come together. I promise.

So three weeks ago I installed my own RO system. The taste of my water was now terrific. My coffee tasted better. Everything was wonderful. Then several days ago, my new RO system became noticeably slow to produce water. Finally, this morning I barely got a half-cup out of it before it slowed to a drip. Rather than tell you everything I did to find a cause, just know that I eventually determined the filters in the RO system are fouled.

In an effort to have some drinking water on hand, I broke out the old Brita water pitcher we used to use. I still had a brand new cartridge for it, which I soaked and installed. I put the Brita under the faucet and tuned on the cold water. I filled the reservoir, only to see the water was nasty brown again visible sediment. The trust I had in the guy who installed my water softener was suddenly fading. HOWEVER, after a few more observations, I don’t believe a water softener malfunction is to blame.

After seeing the nasty water in the Brita reservoir, I filled a plastic cup with what was supposed to be cold water. Lo and behold, my “cold” water was actually quite warm. My first thought was hot-cold crossover. I eliminated any of the faucets as the cause. At the water heater I found that the tee for the cold water supply was very warm. After a few checks, I eliminated the hot water heater as the problem. This is when I finally discovered what I believe is the problem. The warm return water from the radiant heat system was feeding the cold water supply. The return line from the radiant heat joins the supply line from the well water before going to the water heater. Basically, all the water (and associated sediment) in the 11-year-old radiant heat system is mixing with clean water from the well and water softener.

I feel like I was terribly deceived by a few folks during the purchasing process for this home, but buyers have little recourse. All I hope for now is a final solution. Standing by for questions and answers.
 

Dana

In the trades
Messages
7,889
Reaction score
509
Points
113
Location
01609
In many states using potable water in the heating system is expressly forbidden, and the radiant floor is heated with a captive loop of water isolated from the the potable side by a heat exchanger. This means there are two pumps, one on the potable side, the other on the heating system side, and the heating system side is operated at ~12psi, lower than the potable water, but high enough to limit cavitation on the pumps, and easy on the valves, etc.

hydronic-hot-water-heat-exchanger-wm.jpg


Whether the heating loop needs a thermostatic mixing valve or not depends on the system design, the heat load, and the BTU/ft^2 you can get out of the available floor at whatever temperature, etc.

With the heating water isolated it doesn't need or want to be replaced very often, and it doesn't contaminate the potable water. If the system has been using potable water, iron pumps & valves can't be used on the heating system (they'll have a short lifespan due to corrosion), and that will remain true if an oxygen permeable PEX was used for the system piping. Bronze or plastic pumps would need to be used on both sides of the heat exchanger.

That's how it SHOULD be done, and it's eliminates any possibility of feeding the (lower pressure) heating system water into any part of the (higher pressure) potable side. But there are a lot of so-called "open" radiant systems using potable water in the heating plumbing in states where that is allowed.

Does the heating system keep up at cold temperatures?

What is the water heater temperature set to?
 

Chris Haas

New Member
Messages
4
Reaction score
0
Points
1
Location
Pennsylvania
Dana, thanks for the prompt and detailed reply. I plan to learn if Pennsylvania is(was) one of the states prohibiting the use of potable water with radiant heat. If so, I will make some additional calls to see if I have any recourse with either the installer OR my home inspector (confidence is low). In terms of a solution, the schematic will be a tremendous help, especially if I can find someone around here who has experience with this type of system. Since starting this thread, I made several phone calls with no luck.

Regarding the ability of my system to keep up at cold temperatures, that's difficult for me to assess with any objectivity. I'm less than enthused about my utility bills so far, mostly because the seller bragged about never paying more than certain dollar amount per month, while I'm averaging well over twice that amount in my first three months in the house (albeit in late fall and into winter). Perhaps the difference will be made up during warmer weather and after I've been here 12 months, at which time I can get on the utility company's 'budget' program. Only time will tell. But to answer your question, the system runs excessively LONG when outside temps are below, say 20-25 degrees.

My water heater is set at 135 degrees (no kids in the house). It frequently displays a code (E05) indicating lower element failure. However, I was provided documentation from the company that maintained the water heater (via seller's disclosure) that this was normal because the water heater is wired such that the upper and lower elements fire simultaneously. It looked official, so I believed it. During really cold temps, when the pump(s) and water heater are working overtime, I experienced infrequent E04 codes (upper element failure). The first time I replaced the element. The next time, I learned to simply power down the water heater for a minute or so, then fire it back up. GE is prepared to send me a new electronic controller for free, but I'm waiting until I get the more obvious issues fixed first.
 

Jadnashua

Retired Defense Industry Engineer xxx
Messages
32,771
Reaction score
1,191
Points
113
Location
New England
Considering that the radiant heating loop may end up being stagnant for many months over the summer, why would anyone want it mixing into your cold water supply? There are good reasons why the two should be isolated.

While there are some WH that are designed for space heating as well, most of them are not designed for the continuous use you may need when it is cold out. FWIW, in most places, heating with electricity is one of the costlier ways of doing it.

Do you know what the pipes used for your radiant are made of? A typical WH is not really designed for space heating, and its lifetime will be shortened. Hard to say how long it will last. As Dana mentioned, if it is pex, it needs to be one with an O2 barrier, or it will be adding O2 into the water, and rust out typical pumps.

As Dana mentioned, a potable water system cannot use CI or iron or steel materials. They work in a normal boiler situation because it is not seeing fresh water all of the time. Your well may or may not have much dissolved oxygen in it, but still, you don't want iron components, as they will rust. Heat that water, and they'll rust faster in the presence of any oxygen. A boiler circuit can work with less expensive iron or steel components because shortly after filling the system, all of the oxygen gets used up (by rusting things), and is no longer free to continue that, so it stops.
 

Dana

In the trades
Messages
7,889
Reaction score
509
Points
113
Location
01609
Where is the pump located in that diagram?

If you can easily move the cold water feed line from the well to the "To House" side of the tee by the water heater, with a check valve between where it tees in and where the radiant return tees in at the water heater you shouldn't have any mixing of the cold with the radiant return.

The 135F storage temperature is not a problem. Independent of the storage temperature, code demands installing a tempering valve (or thermostatic mixing valve) between the water heater and the hot water distribution plumbing to any sinks/tubs/shower, but could be left untempered for lines to dishwashers or clothes washers. This is worth doing even if there are no kids in the house.

It's still worth re-configuring the heating with an isolating heat exchanger to keep the potable water from mixing with heating system water altogether. Alternatively, may be better or easier to simply install an electric boiler for the heating system, and using the water heater only for hot water, re-configuring the water heater to operate the elements as-designed. How many watts per element? (That would clearly put an upper bound on the size the electric boiler needed to be.) If it's a pair of 4500 watters that's 9kw. A 9kw electric boiler such as the Electro EMB-S-9 is under a grand at internet pricing.

It's also possible that you can go even smaller on the boiler, not that it would save a lot on the boiler end, but if you're running out of capacity at the breaker panel it could be an issue. You can come up with a reasonable estimate of the actual heat load by comparing power use against heating degree-day data between meter readings, using the methodology spelled out here.
 

Chris Haas

New Member
Messages
4
Reaction score
0
Points
1
Location
Pennsylvania
Dana - the pumps for both zones are essentially where you see the "TO Radiant heat (Supply)" banner on my diagram.

I sincerely appreciate all the information shared here. Isolating the systems is clearly in my best interest, and I will do just that when the weather breaks. There is some temptation to go with a gas boiler, which would require the addition of a storage tank and plumbing it to the boiler. I need to analyze the advantages and disadvantages of each. I guess that dream garage will just have to wait :mad:

Based on a couple online resources, I determined a rough requirement for just under 72,000 BTUs (heating two floors totaling 2,600 square feet in a moderate climate). I will take the recommendation under advisement for the Electro brand boiler, but I'm also considering a SlantFin Monitron based on a few reviews I found. I will also look at reducing the size of the water heater since 80 gallons is far more than I will ever need for the two of us.

As always, I'm open to any additional suggestions you might have. Thanks again!
 

Dana

In the trades
Messages
7,889
Reaction score
509
Points
113
Location
01609
That's an extremely rough heat load estimation- only the order of magnitude is correct. Unless you insist on sleeping with some windows open, 72,000 BTU/hr would be the heat load of a 2600' TENT in a moderate climate, not a house that was built to code-minimum standards (probably IRC 2003) in 2005.

A typical 2600' 2x6/R19 house with U0.35 double-panes would come in at about 30-35,000 BTU/hr @ 0F, and it's not clear if 0F would be anywhere near your 99% outside design temperature. With foundation insulation it might come in under 30,000 BTU/hr @ 0.

Also note, assuming the hard-wired double- elements are (4500 + 4500= )9000 watts, note that 9000 watts (x 3.412 BTU/hr per watt=) 30,708BTU/hr- do you really think you'll need anywhere near 72,000 BTU/hr?

Since you have a heating history on the place, run a power-use based load calculation at your 99% outside design temp to get a handle on it. You might be able to get away with the smallest of the line 8kw Monitron, but you'll almost certainly do just fine with the 10kw version, and it would be downright insane to install the 20kw or 24kw versions, since that may even require upgrading the power service to your house (!).

With any house heated with an electric boiler driving radiant floors it's worth considering using a floor thermostat to control the floor temperature to some comfy level, but buy ductless mini-split heat pumps to control the room temperture. A 73F floor in a 68F room is mighty comfortable, but is emitting a lot of heat, and using a lot of power. A 73F floor in a 73F room is even more comfortable but is using essentially no power to keep the floor warm. A better class ductless mini-split keeping the room at 73F would use about 1/3 the amount of electricity that an electric boiler would use keeping the place at 68F. A mini-split sized correctly for your heating loads will also provide very high efficiency air conditioning.

When we have a better idea about the whole-house heat load (based on power use) we can get more specific about which electric boiler makes sense, and more specific about heat pump solutions too.

There are hydronic reversible chiller solutions (eg a 2 - 3 ton Chilltrix ) that could run your floor at mini-split type efficiency too, but it's difficult to find local support and competent design talent in most places. A really brave & talented DIYer can probably handle it, but it's a lot harder to get it right (= designing the system so that it is both highly efficient and covers the load) than sizing & dropping in an electric boiler.
 

Phil Reierstad

New Member
Messages
1
Reaction score
0
Points
1
Location
Vancouver,British Columbia,Canada
Here's a rudimentary schematic of my existing system....

View attachment 38290
To me, based on the information provided, the best solution is a separate electric boiler dedicated to the space heating, but , like some of the commenters have recommended, an accurate heat loss calculation for the structure is important to solve the issue. You would have to see if the existing electrical supply would allow for this, smaller domestic hwt, and separate electric boiler, if possible. Continuously introducing oxygen rich make up water into a hydronic heating system is a big no-no, even if all critical components are non-ferrous, and/or engineered to prevent oxygen absorption due to the physics of various types of hydronic heating systems.

Regards,Phil.
 

Fitter30

Well-Known Member
Messages
4,260
Reaction score
769
Points
113
Location
Peace valley missouri
Heating systems don't like fresh water especially one that has high tds. Sediments should be taken out with a whole house filter like a big blue filter 4.5x 20"housing with 30 micron then maybe a second one in series with a 1 micron.
minerals ( TDS) should be taken out by the softener but it has to be setup correctly. Pull a couple of faucet aerators see whats in them. Radiate floor systems usually have multiple zones water temp runs 5-10* over room setpoints. Flooring and floor coverings are very important they have to rated for radiate and have temp limits. Do you have any idea how much tubing was used and the lenghts, size of tubing, lenghts of loops. Some electric companys offer a energy audit which includes a blower door test ( tells how air tight the house is) my coop charge $50 virus has them shut down for now. Boilers have to find out how much total cost of electric per watt with taxs, type of gas btu content and total cost x efficiency of boiler.
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks