Many years of issues with radiant floor heat.
Where to start? Geez, I’m an idiot. My issue has been ongoing for years and I don’t even really have a good excuse for not addressing it properly sooner. It’s a long drawn out tail, but I will try to keep it brief and to the point.
25 years ago, my wife and I decided to build a new house, and being young and ambitious I took on the task of wiring the entire house, doing most of the plumbing including an inground septic system, all of the landscaping including retaining walls and unfortunately the heating.
At that time, at least to me, in floor radiant heating seemed like space age technology that no one where I lived seem to have a clue. I was intrigued with the thought of warm floors & feet. It was the birth of the Internet and I decided to use it to learn what I could and ultimately relied on a company out of Vermont to ship me all of my tubing, reflectors, Circulators and etc. for my radiant floor heat system. They also did the design based off the blueprints I provided for the square footage of the house.
The problem: it just has never worked properly, or it may be that things were not sized properly. The main issue I’m having is any time that the temperature drops below 20°F which it does often where I live, my great room with high ceilings and lots of windows, struggles to achieve anything above 62°. Today as I sit writing this, it is 11°F and my great room is at 61°. When I go into the basement and check the system, all of my circulators are running for each of my 3 zones. My Combi boiler has the water temperature up to 140°F and the return temperature on each zone is showing roughly 130° for a 10° differential.
My tubing is 7/8 inch staple up with continuous aluminum plates through out the house with hardwood floors being the majority of all the flooring material. My guess is I just do not have enough radiant tubes, creating enough BTUs to heat my great room properly. The other zones in the house work ok especially ones that have doors that isolate themselves from the huge great room. For example my master bedroom with carpeting has no problem heating at all but the kitchen dining room area that’s a separate zone is negatively affected by the giant great room and the heating deficiencies.
I should’ve the addressed this year’s earlier but I’ve always felt frustrated in the fact that not many people seem to have a clue here about my issues and radiant floor heat in general. I’m getting closer to retirement and do not want to have my house cold as I get older.
My question to the forum is, The circulators today have been running pretty much nonstop because of the Arctic cold and wind. Is the 10° differential possibly telling me something? I’ve read a little bit that says that it should be more like 20°? Should I possibly throttle down a return valve to slow the circulate Down to possibly get more heat/BTU’s out of the water? Or is it just that I need more tubing in my floor Joyce spaces? As a sidenote all of the joices bays have a reflective bubble wrap install insulation stapled up underneath each bay.
My hope is there’s an easy fix, but I’m a realest. Any help here would be greatly appreciated.
Comments
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you would need to do a heat load calc to know the exact answer. Are there two tube runs in each bay. Is the problem area over a basement? Bubble foil alone may not be enough insulation.
What temperature is the supply set at? Increasing the supply temperature may be a simple way to increase floor output.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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there is one tube run per Joyce bay.
Basement is below and previously was a heated finished living space when my kids where kids. Now the concrete slab is unheated and unused space.
Supply temp is set at 140*. I remember being told years ago by supplier, that my tubing had a 150* max. Can I/should I run it up to max?
Is the 10* differential not an issue?
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The 10F delta T is not an issue. In fact, a 20F delta T would make your problem worse! You want a higher average water temp, not lower.
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I suspected a single run when you mentioned 3/4 tube.
Can you see the data on the tube? If it is any version of Pex, it should handle 180 f or more.
The heat output limitation will be the floor surface temperature. Stay below 82F for a floor that is comfortable in bare feet. With wide spacing like you have you will see stripes of warm spots right over the tube.
Generally you want at least a 6” fiberglass batt below a system like that.
And no, 1/2” bubble foil is not equal to a 6” batt 😏
There are cases where radiant floor alone will not adequately heat a room or space. 10 delta is fine as @Hot_water_fan mentioned
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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Post some photos of your boiler, circulators, manifolds, etc
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I will take photos tomorrow
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Add some baseboard or radiation and create an additional zone. Put a 2-stage thermostat make stage 1 the radiant and stage 2 the baseboard.
I doubt you will get the floor hot enough to satisfy the heat loss without making the floor uncomfortably warm
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Ah, yet another Radiantec system that never worked. 3rd one this week. The 10* delta is not an issue and slowing the flow would make it worse. You can either turn the water temp up, or add more tubing and plates. Your finished floor and surface temp will determine which is the proper solution.
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The heat output of the floor is entirely determined by the surface temperature of the floor.
If you need more heat, you want to raise the temperature of the floor. The simplest way to do that is to increase the water temperature.
At a certain point the floor will get so hot that it's no longer comfortable to stand on. At that point, it's doing all it can. If the room is still uncomfortable you have to look to other heat sources like radiators, baseboard heat, convectors, etc.
If increasing the water temperature doesn't get the heat output to where the room is comfortable, it may be simplest to add another heat source like a radiator rather than redoing the floor.
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Radiantec® strikes again! Definitely ADD insulation below the radiant tubing! Reflective bubble wrap is not effective for 'driving' the heat UP. The great room with high ceilings and much window glass area will always be a struggle. 10°F delta t is fine. Floor surface temp should not be above 84°F. Adding supplemental radiation might be required. Panel rads?
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Need real insulation. with underfloor radiant systems, generally speaking it is ok to raise the supply temperature higher. The max you are using is a rule of thumb max thrown around for infloor heat, you have underfloor with a single tube in each bay, it will require a higher supply temp, or more tubing, and either way real insulation.
If it were my house I would probably turn up that supply temperature to 160 because it is the easiest change to make. Keep in mind if the plates are truly continuous, as the pipe expands and contracts it is probably really noisy? another possibility since you said the plates run continuous is that tubing has popped out of the plates and is not transferring heat in several areas.
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Before throwing more heat at the problem, I would start with a blower door test and some air sealing. There is a good chance that air leaks in the great room is the source of the problem. For example, I had a hallway with a bunch of old windows with storms that was always cold. Never felt drafty so I wrote it down as it is what it is and never looked more in detail. Finally got fed up and decided to do something about. Re-caulked the exterior frame of the windows and caulked the storms. After $20 of caulk, the place warmed up enough that I had to turn down the rad.
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If I recall some RT systems called for non barrier tubing and a water heater as the heat source. Making any upgrades very difficult.
Miss Hall's School service mechanic, greenhouse manager, teacher, dog walker and designated driver
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"Definitely ADD insulation below the radiant tubing!"
This sentiment has been expressed a couple of times and I want to caution about it. This isn't going to materially increase the floor temperature, which is the only way to increase the amount of heat going into the space above the floor.
Right now the water is dropping 10F. Let's say half the heat is going up and half down, and we could cut the amount going down to zero by insulating below. What would happen is the heat dispersed by the circuit would be cut in half, the temperature drop would be cut in half to 5F. The average temperature of the surface would increase by 2.5F. That increase would give a modest increase in the heat output of the floor, but you could get the same increase simply by upping the water temperature.
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Here are some photos
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I will need to get a ladder to see if I can get the tubing info.
I was initially told by the idiots “Radiant Tech” that sold me everything that there was no need to insulate the bays if under was a heated living space, so i didn’t insulate at all. Then after one winter of heat issues they said to add the bubble wrap insulation……and the basement was finished and now had a drop ceiling and furniture. Now 20+ years later hearing I needed to use 6” batt is infuriating.
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I would cut some 2" foam blocks and spray foam them in those rim joist spaces. If that is what we are looking at?
Then the fiberglass pieces over that. Anywhere you have a joist or rim board you have a potential infiltration. Spray foam can really help cut down on air leaks.
Raising the temperature is quick and easy, ideally I'd like to lower the temperature to boost efficiency and look to limit downward transfer, leaks out the joist ends, etc. The more you improve the shell, lower the losses, the lower the heating costs.
The heat output limitation will be the one tube per space. If you look at that floor with an infrared camera you would see some wide temperature variance across the surface.
Common transfer plate jobs have a 4" wide plate 8" on center, two in each bay.
Any idea of the flow rate in the loops? 2.5 gpm with 3/4" tube 16" on center gets you about 15 BTU/ sq. ft output. That is a low number unless you have a very efficient home.
Increasing the flow rate is another way to get a bit more heat output. If those are multi speed pumps, crank them up all the way. I think some of that companies pex was actually 7/8". That is why the odd hose clamp fittings.
Here is a pic of 6" on center radiant. And a shot where the tubes are 12" apart. I suspect yours are 16" apart
More rubber on the road, so to speak.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
"Increasing the flow rate is another way to get a bit more heat output."
He's already got only a 10F delta. Increasing the flow will decrease that delta, but there just isn't much room to make the average temperature higher.
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Anyone notice those "bronze" colored circulators? For non O2 barrier tubing maybe? That manifold is "pure" Radiantec. So is 7/8" (o.d.) pipe. I can also guarantee that those underfloor conduction "plates" are site- shaped aluminum flashing. I don't believe there are any extrusion plates for "snap-in" 3/4" i.d. pex pipe for residential applications. Isn't that an interesting concrete sill plate? Maybe it was formed when pouring the foundation walls. Unusual.
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In hind sight it was a bad move having Radiantec spec my heat. I definitely gambled and lost. For 20+ years it’s been deficient and apparently they have earned a reputation here, from your comments of 3 of their systems having issues this week. In the early 2000’s they were about it for info on the web.
When the outdoor temps are above 20* the system works great, we love the warm floors while having morning coffee in the winter. The somewhat good news is we recently added AC to our home via mini splits, which also provides additional heat “like now” when it gets Really cold, at least until it drops below 0*F and they stop making heat.
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Yes, I initially was heating with a Polaris 100kBtu hot water tank for probably 15 years. Just 4-5 years ago the tank went bad and switched to the combi. RT should be sued if they are still in business. What a awful way to do business, sell people on inferior system and components.
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Raising the max water temperature sounds like the easiest solution. I will have to dig into the exact tubing my system has, but recall it having a 150*f max.
If 150*f is my tubing max, am I ok to bump up against the 150? Or should I stick to the 140* I’m at now?
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Gezz, that truly makes me sick. You can add Pennsylvania to the list of botched designs now.
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I will have to dig out the specs on my components and get back to you. I think my tubing is 7/8”, but need to double check. The pumps aren’t multi speed. Will check on flow rates. Can you elaborate on where the rim joist space is, sorry uncertain that terminology
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Would it help @coldhouse to turn on the one basement zone and add additional heated mass inside the house in order to help heat up the house? Just wondering since I saw he mentioned earlier that the space was previously heated and I see now in one of the photos provided that the zone is valved off and possibly shut off at the thermostat since the space is no longer occupied by family members.
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here are some of my spec’s. I will dig for more tomorrow.
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Googling I found a spec sheet for Dura-Poly XL:
It says 60 PSI at 180F.
It looks like from the sheet that the first floor is 3300 SF? At 48,000 BTU/hr that's 14.5 BTU/sf/hr, that's not crazy.
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I sincerely can't wrap my head around how Radiantec is still in business. I've seen literal hundreds of their systems and at least 75% of them have been less than satisfactory. They put on a good show by giving you all the paperwork and "calculations", but they're always wrong. I feel like it'd be easier just to do it correctly, but I suppose then they'd lose their proprietary nature.
As a side note, whoever installed this new boiler for you piped it wrong so that's probably not helping matters either. Is the boiler set to 140* or are the zones actually seeing 140*?
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Yes, it is a Radiantec and 7/8" non O2 barrier tubing. I think the plates were pre-formed, but I'm not positive since that was many years ago that I did the installation. The manifold in the concrete was in a wood box and poured in place.
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I have also given this consideration, but since having had check valve issues with that zone and kids moving out, I just shut the zone down.
Fast forward a few years when the Hot water tank doing the heating quit, I had a plumber friend do the installation of the Combi. At that time I was told that the 3/4" manifold was sized too small for the BTU's required to heat the house "I thought may be an Ah-Ha moment" so we upsized the supply and manifold supply & return to 1.25" and replaced all the checks. It made no improvements to my situation upsizing to 1.25". Replacing the checks did help with recirculation issues.
This is another one of the many problems with my system. Since doing the manifold changes, the concrete/basement zone will not circulate. The plumber buddy says the pump is too small and needs upsized, though it worked for years with the 3/4" manifold & the Hot water tank. Summer came last year before I pulled the trigger on a new pump. I need to revisit the basement zone, but feel its a low priority since its an unoccupied space most of the time. If keeping the basement heated is the answer to help the upstairs zones, then I need to address it. What complicates the basement also, is plumber buddy said I shouldn't be sending 140* water to a concrete slab and said this after we just installed the new header, when a mixer could have been added. It's all frustrating, beyond frustrating. I like doing & having things done right and all of this heating system is so wrong………. I wish I could start over, but that is not possible without piles of dough at a time when piles of dough do not exist.
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I cannot find any info on that brand of tubing? If it was manufactured and listed to any spec, it is supposed to be printed on the tube every 2’or so
Sorry about the hassles, it seems you have tried some options.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Getting the basement heat running again will definitely help with the main floor heat. I don't believe that you would need a different circulator. Sounds like it is airbound to me. Your buddy was right, you do not want to run 140° thru your concrete so it will need a mix valve.
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The first floor/above the basement is 1,646 sq'. I just emailed the company shown to make the tubing "NIBCO" and see what they can tell me about the max temp. If you look at the design sheets, they all show 150*F max, but it is handwritten, not a spec sheet.
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Each zone has a thermometer at the supply pipe right before the circulator "see pics above" as well as one on the return side of each zone. Can you let me know what is piped wrong, I am hoping to get this system to be as right as it can be.
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No hassels, thanks for being here to help! I am going to try tonight or tomorrow to get a picture of the tubing to confirm the design paper work saying its 7/8" Dura-Poly XL. I also emailed a company "Nibco" who possibly made it? I'll report back .
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Radiantec put a lot of that pipe "out there." I've seen it frequently in my career. So you aren't the only one. You are right about NIBCO. I don't know if the 7/8" is i.d. or o.d. Your system was originally an open system with a Polaris domestic hot water tank doing heating for both dhw and radiant floor, hence the bronze circulators for oxygenated water. I believe that has changed now with the replacement LAARS boiler. That is good.
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Nibco replied and said they didn't start making PEX until 2005 and mine would have been pre 2002. I will get eyes on the tubing when I can get a chance and report back.
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Yes, the system used to be both domestic hot and heating completely commingled. The cold water supply would first travel through the entire heating system prior to feeding the cold water inlet of the hot water tank. It did work for years, just never great from a heating standpoint. The Laars now does both, but separately. The Laars has its shortcomings as well. Being on a well here, with the on demand Laars hot water is bad. I have to readjust my water temp the entire time I shower……….. as the water pressure changes, so does the temp of my shower!
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Do you know the max temp for that tubing? Nibco did not make mine.
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