Hi:
I’m about to install a ceramic floor in a kitchen and hallway area (about 120 sf). My wife wants me to install electric radiant mats under the tile. I have some reservations about this, mainly whether it will be a lot more expensive than the hot water baseboard that’s already present in the room, the cost (~$1000), the relatively short guaranteed lifetime for the mat, and the extra thickness of the floor due to the mat.
I was wondering whether it would be worth rerouting the hot water feed to the hot water baseboard already in the kitchen into loops of PEX under the kitchen floor that would provide floor heating instead. The basement below is unfinished and provides easy access to the space between the joists. ‘Any one have experience with radiant heating in one room, with hot water baseboard in the remainder of the house, all running off the same boiler at the same temperature?
Thanks
Replies
I have that same setup in the kitchen of my 25 year old house. I have radiators in the kitchen in a couple of unique places and the rest of the heat under the ceramic tile comes from simply routing the return lines back and forth through the floor joist bays and insulating under them with 6" fiberglass.
The kitchen is about 400 sq. ft. The tile is toasty warm when the heat is on. Just the perfect temperature. I have 1 1/4" of plywood under the tile.
This was before Pex, when copper was cheap and I did all the work myself, so it wasn't such a big deal. It was the first time I had tried it, so I didn't know exactly how it would work. I was very pleasantly surprised at how well it functions.
Keep in mind that copper is a much better heat radiator than Pex. If you use heat plates with the Pex, you can't use water at the temperatures you use now. Therefore your results may vary....but I do know it works great with 3/4" copper. I would just go with the copper instead of the Pex if I were you.
Thanks for your comment. I couldn't think of a reason why it wouldn't work. Your point about copper is well taken. If it transfers heat better, it might be a better choice.
Don't know why you'd use copper anymore. It's about 5 times the price of pex + a lot more work. Menards sells 250 rolls of barrier pex for about 70 bucks. Even if pex isn't as good a conductor as copper, it isn't like you lose the heat. It all winds up in your house or back to the boiler.
I think you're missing the whole point. He wants to lose the heat ( in the area under the floor he is trying to heat ) He's not talking about the rest of the house.
3/4" copper will radiate a lot more heat than Pex tubing as it passes through the floor joist bays. That's why they make the core of fin tube radiators out of copper instead of Pex!
If the water temperature going to his radiators is 160 - 180 degrees or so, he will have a nice warm tile floor without doing anything expensive or exotic.
With water at that temperature, you don't want to use any type of heat plate. Just suspending the copper tubing with regular plastic hangers under the subfloor works perfectly in a situation like his.
Running copper in a small area like that is not that costly.
Say what? This is the first time I've heard of someone pushing copper in a radiant floor application. Why? It's five times the cost for materials and much more work. Pex is the standard for radiant heat...why reinvent the wheel? It works. Suspended tube systems are cheap and they work. Did you check out the link I posted? Ask 100 plumbers if they use pex or copper in radiant floors and all 100 will say pex. What are you talking about expensive and exotic for? I don't follow you.
He asked about a certain situation and I gave him a recommendation based on my personal experience which includes 35 years of installing radiant heating systems in over 5000 homes. We use about 50,000 feet of Pex a year, so I'm pretty familiar with the stuff.
I told him why I would use copper under the floor area he wants to heat. I thought I made it pretty clear why I would do that.
If you want to do it another way, fine.
BTW, most "plumbers" don't know much about radiant heat anyway, so they might say almost anything.
I did something similar, only I have cast iron radiators. My radiators are supplied with pex, and I tapped into the one supplying the kitchen radiator and looped it under the kitchen floor. Two runs per joist cavity, with bubble foil beneath. Works great. My boiler is set at 140, so it could be a bit hotter. Cost me less than $200 for the tubing and the insulation, though I already had the tools to crimp pex fittings. It's made a world of difference in the comfort level of my kitchen.
Your situation is a little different in that you have fin tubes, which have a shorter response time. Worst case you have to add a zone. But I would wholeheartedly recommend it over the electric mat.
Post #8 in this thread (http://forums.jlconline.com/forums/showthread.php?s=f54b3b7e3a5b329c69715fa88ebbac14&t=45758) has some photos of a suspended tube system.
Radiant hydronic floors are usually run at a lower temp than e.g. hydronic baseboard. Radiant floors around 90-105 roughly while baseboard is often much higher temp. You could install a 3 way valve maybe to reduce the temp to the floor. Your hydronic floor will boost your floor thickness by much more than the electric matt ... which I think would be a minor impact on thickness (like maybe 1/16inch, I'd think) vs. the radiant floor will add 3/4" to the floor ... unless you go underneath (which come to think of it, may be your more likely choice; I did mine on top. The electric heat Btu for Btu is likely substantially more expensive than your other heat. How you are able to configure your hydronic system may impact your final choice. Just a little food for thought to get you started here. Others should offer some other helpful thoughts.
"Radiant hydronic floors are usually run at a lower temp than e.g. hydronic baseboard. Radiant floors around 90-105 roughly while baseboard is often much higher temp."Suspended tube systems run at a much higher temp than 90 to 105. Mine is working at 140 and I think it could be warmer yet.
Good point, although the radiant floor will still probably run cooler than baseboard. In your neck of the woods, baseboard will go up to 180 degF easily.
You don't need to worry about the lifetime of the electric mats, they have a very long life. 1/4" is all the mats add to the floor height. Control is via a wall stat with infloor sensor.
Avoid using copper in the "cement" as it can have a reaction and end up with pin holes. Levitown near Philly had this problem with many of the in floor systems there but the people loved it till it failed!
For the "wet" infloor in the concrete you will add at best an inch. You could install it under the floor, a little slower to react but will work. Make sure you insulate to direct the heat where you want it.
I suspect an underfloor system will react no slower than an infloor w/ e.g. gypcrete or cement based bed. I've never heard of the cement based taking only an inch max. I've always thought they take say a minimum of 1 1/2 inches. What size tubing? 3/8?
I meant to say a minimum of an 1" and thats pushing it to the very thin side. Only a touch slower due to the layer or wood for the sub-floor. Makes the insulation more important for directing the heat.
We have radiant thermoplastic mats in our bathrooms that are great at heating the rooms, inexpensive to run, and add very little to the floor height (the thickness of the wire running along the edges).
That said, if anything goes wrong we would have to rip up the floor. Also, if future owners decide to change the flooring then the radiant heat could get damaged, even though it is under a mud base. If you have access to the floor from underneath I think it makes long term sense to put the radiant heat there, especially since you already have the system in place for it. Given that you have the option of putting in traditional radiant floor heating, I would do it that way.
You normally need mixing valves to use water no more than 114° for floor radiant hydronic heat.
As I scratch my head on this here, I can't remember all the reasons why tho.
I believe one is efficiency - you could end up with the basement under this getting 3/4ths of the heat delivery unless you really do some good insulating under this.
Another is thermal integrity of all associated materials. How long will the thinset and tile remain adhered well to the subfloor when using higher temps? Will having some areas at 70° with others at 120° a few inches away be detrimental to the life of the system?
Maybe somebody else would know.
Controlling comfort level would be a concern to think on - what are your existing zone controls? Will making the kitchen comfortable with this setup end up making the living room too warm or too cold? Will this make the floor end up trying to heat adjoining rooms and waste heat energy?
You are essentially doing an experiential thing.
it might work fine, or it might be an expensive disaster.
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I think you guys are trying to scare the OP. All he has to do is snake one run of 3/4" copper down each floor joist bay as a return to the boiler from his radiators.
As I said, I have exactly the same setup in my own house and it works perfectly. I don't know how anything could be easier to do and get such good results.
All he is doing is creating a cheap radiator below his floor. We are talking about 110 feet or so of 3/4" copper in his situation. That certainly isn't going to break the bank.
To the OP...As I said before, you will need water temps in the 160-180 degree range to your radiators. If you have fin tube radiators, that's probably the temps you have.
Go for it. You had the right idea in the first place....but use copper under the floor area. You probably have 3/4" copper there now, so it's just a simple cut into the return line.
"I think you guys are trying to scare the OP. All he has to do is snake one run of 3/4" copper down each floor joist bay as a return to the boiler from his radiators.As I said, I have exactly the same setup in my own house and it works perfectly. I don't know how anything could be easier to do and get such good results."Some other guy might be, but I'm just sharing fact based information. He can make up his own mind. If you know anything at all about systems in houses and how to design them, you know that there is not a good reason to assume that what works perfectly in your house may come close to working in his house. You have no idea what the layout is there. Every variable in the calculations might be 100% different. This is like saying, "I painted my log home purple and it looks fine to me so it will for you on your stone cottage too."
or "I used ICF forms for my foundation so you should too" not knowing that the OP might have a slab on grade.
or to tell somebody, " My archy dimensional shingles work great for me so they will do you fine" without realizing that the OP has a 2/12 roof.
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My father the plumber, when he ran a hot water heat system he would always run a small section of fintube under the kitchen sink area. "gotta keep the little lady's feet warm"
Run 3/4 copper naked, in the center of each bay, no need to run under the base cabinets, just the useable floor area. Hang it down under the bay area, hang it loose, give it room to move. Bingo!!! Lots of BTU's, maybe a little lower return temp to the boiler. Run after you supplied the rad's, don't steal BTU from those!!
"Run after you supplied the rad's, don't steal BTU from those!!"That would solve any concern about water too hot and no mixing valves - just using the water on the way back to the boiler to dump the last few btus into the floor warming. Would not make the cellar below too warm.
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Yep!
"Run after you supplied the rad's, don't steal BTU from those!!"
That would solve any concern about water too hot and no mixing valves - just using the water on the way back to the boiler to dump the last few btus into the floor warming. Would not make the cellar below too warm.
Cameraman just repeated almost word for word what I told the OP. You didn't believe it before and now you are finally enlightened??
I think you need to stick with giving advice about things you are familiar with!
I didn't read all the post, had to go back and read your!
Your dead on! IMO.
I have quite a few lengths of 3/4 fintube that I salvaged.
I plan to run that, I don't have to make it solid fin, I can break it up in sections to make a even coverage. That part of the basement is colder than the rest, will help both up and down.
He may have said what you INTENDED TO SAY or maybe WHAT YOU WERE THINKING but you never said anything about running it off AFTER the radiator when it was cooler, and you specifically referred to a possibilty of him running 160° water through copper. I took the main thrust of your position to be arguing for the use of copper on this instead of PEX, a subject I never even commented on as I didn't see that it much mattered for this project.So if I appear suddenly more enlightened, it was because Cameraman said sensible things that had never been introduced to the conversation. Things that would make a big diff in whether this was a help or a problem. Things that answered at least half the concerns I would have if I were doing this job professionally. Things that you might have intended to say, or had considered, but never once mentioned.So why don't you just add to the conversation without taking my neglect of you so personally. I did not take a position of arguing with you.What I did is the same thing I do as a GC or a designer. I brought up goals and concerns that needed to be adressed to my satisfaction if I were to sign off on going ahead with the plan. Then various subs on the job present ways of dealing with those concerns and we work together to craft a plan that we know will do the job without causing other problems. every sub I work with knows more about his specialty than I do, but I bring it all together. I don't get too narrow of a focus on only the immediate "heat this floor". I bring up questions and let them be answered.In this little conversation, Cameraman answered some of them.Sounds to me like you are a prima dona on jobs. Play your way or no way and pat you on the back for having all the good ideas. Get jealous and throw a jealous tizzy if anyone else contributes something good or explains it better. You want to use copper on this? Fine, Doesn't bother me if he uses copper. Personally I'd rather not do that much soldering up overhead in a 14" space, but it's your idea - take the ball and run with it.
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Thanks everyone for your opinions. They've been very helpful and informative. The hot water baseboard in the kitchen is the last one in the circuit, so it seems the ideal place to tap into and to put tubing under the floor between the joists. The rest of the house in that zone (there are three zones in the house altogether) will get the higher temp water as it does now and the remaining Btu's would go into the floor before the water returns to the boiler. The temp set point is 180 degrees in the boiler, though I don't know what the return temp is. However, it may very well be approaching the lower temps normally used in radiant floor systems by the time it gets to that point. I'd plan on insulating to direct the heat between the joists upward toward the kitchen floor in any case.
just make sure the water temp and pressure of your system and the max pressure at the temp of the pex are compatible. Some pex ratings are as low as 150 deg F. I have mixing valves to keep the temp around 120, but I have wood floors. Also, you may not want the floors to be too warm, or your feet will sweat in one room then feel clammy when you go back to the others.---mike...
'Good points. Thanks for mentioning them.
Really? A good grade of an oxygen barrier pex should be in the 100 psi @180 degree area.
My hot water system runs about 20 pounds, before you should be worried about blowing up your pex, your PRV should be doing it's job.
Any way the OP is talking about running copper, other poster were talking about pex.
Go back and READ my posts. I said to run the return lines back through the floor joists. Plain and simple, if you take time to read and comprehend.
My beef with you is that you so often jump on somebodies advice when you don't really know what you're talking about.
I never comment unless I've had personal experience and can offer some constructive advice.
You should try that approach. Have a good day!
I already re-read yours before my last post.Beef all you want. I did not criticize your advice so you are just paranoid and taking it personal that somebody didn't notice you. And when I enter a conversation where I don't know as much as I should I am careful about how I word things so maybe you should be the one to re-read things. Probably five times a day i will state something here that another person later restates and it is then when it gets noticed, because they explain it different of better. I don't get all bent like you have here just because somebody didn't notice that I said something first.
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Piffin, your numbers here are completely incorrect.Infloor radiant heat can run at a wide variety of temperatures depending on installation method.suspended tube in a joist bay with no plates can easily REQUIRE 160+ degree water to provide adequate heat.using some suspended tube... copper, as BoJangles notes, or much easier to install PEX which will heat up the joist cavity to very nearly the same temperature, or maybe PAP to reduce expansion noise concerns... is a time honored way to get some floor warming into an area that needs a little heat on the way to a baseboard.I don't know where your 114 is coming from, but that's not a number relevant to anything... nothing personal, but it's just not real.low temp heating is great, and high temps have issues in some cases (notably when you are in the thinset itself, you would have to limit to 130 or less), but in some cases high temps can, and really should be used.-------------------------------------
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"I don't know where your 114 is coming from, but that's not a number relevant to anything... nothing personal, but it's just not real."Nothing personal taken.It is coming from memory and designing some of these back about 16 years ago when the technology was new enough that the plumbers here were still afraid of it. I studied a 2"thick book and had consults with a heating engineer to walk the guys thru their fist installs.The system itself can surely handle those temps, but wood floors do not like them. Constantly expoosing woodto high temps degrades the wood and shrinks it.
And I distinctly recall a chart for in slab concrete that and varying mixing temp limits that changed according to the size and spacing of the PEX laid in.
And in all the installs I have seen in slab since, I do not recall one that had the mix higher than 120° cracking of the concrete was a concern - more so before it was fully cured for 90 days. My own runs at 111°F and I would hate to think of water any hotter than that in the floor slab. It is more than warm enough as it is.An overhead in frame floor is certainly differentI think where the difference in your thinking and mine ,may be is that you are looking at what the system can handle and I am approaching it from an overall general design POV where comfort, efficiency, and not ruining the materials at hand are also concerns that the heating guys often overlook. I step back and look at the whole picture while the specialists have a more narrow focus.That said, if you have info to convince me that running at higher temps is more efficient without hurting the goods, I'd love to see it.
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more efficient? no. but in the case of a one room add on doing suspended tube in a joist bay, there is no downside to running the higher temps. You save a ton on material costs and in this type of case, you aren't losing much in efficiency either: it's a small area on a system already running high temps.I doubt you'll find anyone as "anal" as I am about running low temperature systems (I consider 110 average these days) or as concerned with comfort, efficiency, and problem free systems including flooring integrity and a hundred other concerns: but it's not a real concern to worry about "constant stresses" in this type of application: the suspended tube just isn't strong enough to cause any damage (and it's pretty limited in output too). There are literally thousands of these systems running with no such problems... and many with problems too, but they are poor design choices outside of the max temperature of the system itself. Some have had problems with wood floors, but that problem is a bad wood floor install, not the radiant per se. If the moisture content was watched it would have been fine. If you go back and install such a system on an old, well cured floor you definitely are not going to create a new problem there. In gyp/concrete, the hard limit is somewhere between 130 and 140.. I forget the mechanism you are avoiding there, but it's actual concrete integrity, nothing like just cracking. In other systems, such as an above floor sandwich, I stick to a 120-130 max, but frankly that is as much superstition as anything.we've learned a lot in the last 16 years ;)-------------------------------------
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Thanks - I know you know your stuff, having read you before.
You point out that having it suspended instead of direct contact will keep the high temp flow from making the materials too hot. I had thought you were saying previous that 160° in contact was OK.There was another concern I had voiced before.Nobody knows what this house layout is and if the kitchen is isolated form other areas with doors or if it is an open floorplan with good airflow throughout. I am assuming the latter now that OP has said it is all on one zone.But the thought I was considering and would want to KNOW before proceeding is whether adding extra heat to the kitchen would make it too warm while other spaces suffered. This would depend too on where the thermostat control is located also.
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