Water temp for in concrete heating

Tracey

Hi all,

I'm getting ready to pour a concrete floor in my shop. Currently we heat the house and shop with an outdoor wood burning boiler, (Central Boiler), through a heat exchanger forced air system. (House and shop). I would like to install a radiant in floor system when I pour the new floor in my shop. (960 sq. ft)

Question 1;  What temp should the water be in a radiat in floor heating system?  Somewhere I seem to remember reading it should be around 80 degrees or so?

Our boiler runs at around 185 degrees water temp and is not adjustable. When/if the water temp drops to 120 degrees or so, it is quite noticable in the way the blower fan runs inside the house and shop. (the fan runs for longer periods)

Quesion 2; How would I lower the water temp for the in floor system without effecting the house forced air system?

Sorry for the "simple" names/descriptions. I'm definately not a HVAC expert...LOL



Thanks

Charlie from wmass

You need to move this question

It will get more attention under Radiant heating. the temp is based on the tubing spacing and the heat loss for the area. It is also based on the temperature you want to get the room up to. The closer you have the tubing the lower you can run the water temp. Lower temp means less fuel. SO pay for more tubing on the installation and less for fuel for the life of the system.

Tracey

Can I?

Can I move the thread? Unfamailiar with this type of forum. All the other forums I'm a member of a moderator would have to move a thread.

If a mod can move it I would appreciate it. I wasn't sure where to post it and was reading the hot water section when I decided to post.

How would I go about figuring the heat lose?



The tubing spacing is yet to be determined, but I think I had I had figured it at 1 foot spacing with 4 250 foot loops. I'll have to dig out my drawings and refresh my memory.

I guess my main concern is the high water temp being hard on the concrete. Seems like I read somewhere that temps above 80 degrees or so could crystalize the concrete arond the tubing, reducing heat transfer and weaking the concrete. True or false?

This water temp issue will be the deciding factor as to wether I go ahead with the Pex install.

 I already have the tubing, (1/2 in), and the boiler has been heating the house/shop for the last 8 years already, so fuel cost/consumption is a nonissue. It'll just be a change from one style of heat to another.

Charlie from wmass

I will just cut and paste the thread

over to Radiant. Your handle will be the title

Gordy

Temps

 140* is the max for tubing in concrete with no issues.  I do not know where you got the 80* from.  Other than there is a limiting Surface temperature for comfort in high traffic areas, and wood flooring products of 85*.



 You really need to do a heat load calculation, and look at what the radiant floor will service to decide tube spacing, and water temps needed.





 Example being if it were a garage then 1' or even 15" centers may be exceptable depending on load because you will not be walking bare foot in the garage, and notice stripping.



 If it were say a kitchen, or bath where there is high traffic, and bare feet then the centers should be tighter 6" to 9 " to avoid noticable stripping.





 Stripping is a term used to describe when you can feel the areas where the tubing is being the warmest, and the areas between the tubing being the coolest. Tighter spacing keeps the heat even through the whole floor.





 Tighter centers also allows cooler water temps to be used to a degree which translates to less energy needed to heat the floor.  





 But in the end you really need to do that heat load as a first step. This will help you determine if radiant heat can handle the load with out a secondary heat source.  It will determine what water temps you will need to deliver to the floor. And it will determine what flow rates you will need for the loops, which in turn determines the pump sizing to drive the system.

Brad White

Some items to consider

Tracey, I am not sure where you are in the process (you did mention drawings), but the first order of business is insulating below and around the edges of that slab of yours. Yes, it is basic and obvious but I do not know what you know, so would rather not have you (or the lot of us), slapping are foreheads over lost opportunity.



And yes, perform a good heat loss calculation. This will save you aggravation down the road at all points.



Some basic principles once the insulation issue is done, if I may and in no particular order: (And with apologies to Gordy, who covered these as well):



1. The tighter the spacing, the more even the floor temperature.

2. The tighter the spacing, the lower can be the water temperature.

3. The deeper the tubing, the more even the floor temperature. BUT

4. The deeper the tubing, the longer it will take to heat the slab surface.

5. The lower the R value above the tubing (concrete is nearly bupkes in R value), the less even the floor temperature (more "striping"),  Conversely,

6. The higher the R value the more even the floor temperature but it takes warmer water to get it there.

7. The cooler the water temperature, the more even the floor temperature. (Less "Striping"). Conversely

8. The warmer the water, the less even the floor temperature (more "striping").



Sort of a confluence of variables to get under control in the name of the best shop you ever set foot in. I am jealous.



The practical parts you will need beyond tubing and manifolds is a good automatic mixing valve, circulator, controls, slab sensors and space sensors. All work together. The heart of things is the mixing valve. This will blend relatively small amounts of your hot boiler water with larger amounts of recirculated floor water to make it the right temperature -automatically!

EricAune

Find a contractor

You may have a handle on the installation, or you may not. In both cases you have read responses to your questions by some of the best guys in the industry.  The common thread in all of the above is that you need to start with a heat loss calculation.  Whether you decide to do the work yourself to save money or not, either way your best bet is to find a contractor (there is a convenient place located at the top of this page) who will figure this information for you.  Be prepared to at least pay for his/her knowledge, but it is that knowledge you seek...



Good luck. Oh, you are going to like the radiant more than the forced air.   

Gordy

No apologies Brad

  I like your 8 point coverage much better on the pros, and cons of tubing placement with in a plane of concrete.  More importantly I forgot to cover the insulation detail.



 If we had sticky notes on this forum that should be one.



 To many people think you just throw a bunch of pex in concrete, and wahla radiant.





Gordy

Tracey

try again...

Let me try this again.... I spent about a hour typing a reply to this last night and it got lost somewhere between typing and the sumit button... LOL

The 140 degree max puts my mind at ease a little. And now I understand how a mixing valve works. That clears things up considerably.

This project has and still is in the dreaming stage. The shop was built 10+ years ago and the boiler was installed in 2003. I started dreaming about the heated floor when the boiler was installed. I've just been putting off pouring concrete until I could afford it. I've since come to realize I'll probably never be able to actually pay for it out of pocket so I've made up my mind to go to the bank... The drawing I was refering to are just my own drawings of the pex layout, (to scale on graph paper). I did these years ago and still have to find 'em.

Insulation under and around the slab is part of the plan also. 2 in under and probably 4 in around the perimeter. The 4 in is just because I'll be using the 4x6 poles to support forms and will just fill in the gaps between the support poles and inner/outer 2x6's with polystyrene? (Notsure if that's the correct name). A buddy of mine calls it green board.

Did I mention this is a pole building with studs added to support fiberglass insulation and 3/4 in plywood inner walls already in place? I have learned a valuable lesson with this building though. Never, ever build a building and pour a floor later..... This is going to be alotmore work this way than it would've been to do the floor first.

I keep seeing heat load, heat loss. Are these the same thing? Anyone care to explain how I can do these calculations on my own. I'm just the type of person that feels the need to understand how these things are done, not just get the final info from somebody else.

Brad White

Hate it when that happens

losing typed work, that is! The female of my cats, she knows to jump on my lap and with one paw-stroke, wipe out 20 minutes work. Then looks at me and says, "What?"



Ahem. To your questions.

Heat load and heat loss are the same thing.



I am not sure if you said where the shop is, (climate, location, city), but that is a factor of course. Your local code will govern regarding insulation but 2" below and 4" around the perimeter is excellent for our climate at least (MA). I believe our code (newly the IECC) has it as R10 bottom and sides. You beat that on the sides, the more critical of the two dimensions. Extruded polystyrene (XPS) is what you want. Not the "Styrofoam cup" crumbly white stuff. Most XPS is either blue or pink (Dow or Owens-Corning respectively). Green? Maybe a different brand. But the R value should be 5 per inch thickness. That is the key.



Heat loss calculations, how to do them? The attached is an essay I used when teaching at the Boston Architectural College some years back.  OK, you asked!



But here is another Radiant Factoid: We do not yet know what your heat loss is, or if your floor, properly irradiated, will heat it to your needs.  A limit of most radiant floors for personal long-term comfort is a surface temperature of 85 degrees maximum. This corresponds to a BTU per SF of about 35 BTU's per Hour per SF (BTUH/SF) density with the space temperature at 68F.



Truthfully, a more comfortable range is lower, 80-82F surface temperature and about 26 to 30 BTUH per SF in rough numbers. Warmer than 85F and most people feel "flushed", warm on the face and body, because your body surface is about 85F. Met with an 85F surface, your skin's ability to dissipate internal heat is all but stopped.



So what I am suggesting in the above paragraphs is, no matter your heat loss, your available floor should not exceed those surface temperatures nor the heating densities mentioned. If those temperatures and densities cannot meet the heating load, you may have to supplement them in other ways at least on the coldest days.



EDIT: The attachment did not "Stick: at first, so I just posted it.  Here it is.

Ironman

A Couple More Things

If I may add a couple of more things to what my distinguished and very knowledgeable brethren of the fluids have said:



1. You'll need to add a plate heat exchanger between the O.D. boiler and the radiant along with the usual necessary hydronic devices. The reason for this is so that that radiant side can be pressurized. Your boiler is un-pressurized and the radiant side will require pressure for purging, filling and proper operation.



2. I would highly recommend that you use oxygen barrier pex. I would personally use pex-al-pex in a slab, it's easier to work with. If you don't use o2 barrier pex, then you'll have to use a stainless steel pump, as well as all the other components would have to be non-ferrous. Also, glycol and o2 are not a good mix. So if you're planning to add freeze protection, you'd want to use o2 barrier pex.



3. Because a slab is a high mass system, it has what we call a "fly wheel" effect. That means it can take alot to get it going and alot to slow it down when it gets going. If your water temp is not closely controlled to match the load, it can get away and over or under heat very easily. The best way to achieve good control is to have a mixing valve or pump that modulates the water temp in the loop based on outdoor reset. This means that the warmer the outside temp, the cooler the water will be in the loop, and vise versa. I prefer using a variable speed injection pump controlled by an electronic reset control like a Tekmar 356. You don't want to use a constant temp control like a thermostatic mixing valve. That's OK for low mass, but not high mass.



I' got to go for an appoinitment, so that's my $.02 worth for now.

Brad White

Excellent, excellent points, Ironman!

Essential in fact. I glossed over the fact that it is an open system. Good call on all points.

Tracey

Back to school...

Thanks for the essay Brad! Hahaha. It may take me a bit, but I THINK I can digest all those formulas and come up with a close heat loss calculation... Math class was a long time ago... and essay questions to boot...Sheesh! You're gonna make my head hurt. hahaha

I'll try to give you as much info as I can so you can get a better idea about the heat loss. I'm located in northern Missouri. Not in the city so basically no code to worry about. The building is a metal pole building with 1-1/2 in XPS, (see I'm learnin...LOL), between the 2x6 runners, (?horizontal boards running between the poles to screw the sheathing to). Then 2x4 studs on 24in centers with 3-1/2 craft faced fiberglass insulation. Then 3/4 in plywood, (not OSB, good ol normal plywood) interior walls. The roof and interior ceiling is metal sheathing. No insulation at all up there yet. Still debating on roll in fiberglass or just blow in. (Open to suggestions!) One roll up insulated garage door, (9ft W x 8ft H Unknown R value). One walk in door (42 in x 72 in. 1-1/2 xps core, 3/4 in plywood exterior, 1/2 in plywood interior. 14in x 18in single pane window). No other windows in the building.

Tracey

Pressurize?

Ironman, I hadn't thought about the radiant system needing to be pressurized. You say I'll need a plate heat exchanger for that? (I just glanced through the link you posted. I'll check it closer tomorrow when I'm a little more awake. It's4:30am here now...LOL)



I'm not sure if my boiler system would be considered pressurized or not, but I think you are correct because it is vented to outside air. But the pumps create pressure to push the water through the pex and heat exchanger?  Does a radiant system actually need to be pressurized like a cooling system on a car? Does a plate exchanger isolate the the radiant system from my boiler system other than transfering heat? 



I better go to bed so maybe I can make more sense tomorrow.... LOL

RobbieDo

Wood Boiler

You stated that your heating your house and shop from the boiler through a plate heat exchanger. All of the wood boilers that I have installed are a open system, have glycol in them. What is the BTUs the boiler is rated for? Do you have a boiler other than wood hooked up to this system also? I did a very large barn this winter heated with wood boiler, had a backup Buderus boiler and the customer says the system works good. Have to figure if the outside boiler can handle extra load. Great system when installed right.

Brad White

Sorry for the

volley of information! Just figured it was the best way to get it out over a shorter time span. Well, you *did* say you wanted to know the "whys", so, "why not?". I am all about that.



Got Advil?



The biggest wildcard in your building, (most buildings but especially yours), is infiltration, -air leakage plain and simple. Pole buildings are not space capsules nor submarines. Your best insulation thickness means less when you have potential gaps where materials meet. Sort of like having a full-length thick down stadium coat, but leaving the zipper open.



So, some allowance to be made there.



For the roof, assuming it will be finished on the inside, a spray closed-cell urethane is hard to beat, but if in direct sunlight, that roof can get hot hot hot, which can degrade it. I am not a fan of dense-packing (blown in) roof insulation and would take batts as an alternative. But batt insulation needs to be all but perfect (unrealistic), or you can lose half your R value with a few percentage points in gaps. With me here? Integrity of the insulation, the perfection of coverage, beats thickness!



I know you said 960 SF (as I recall), but what are the dimensions inside the "insulation bathtub"? I can draw up a layout for you with various options if you like, no charge. I know you have one, but I can make some alternates easy to see.



Now, remember what I said about upward limits on floor temperature and output? If you have 960 sf (which I will verify when I go back to the earlier posts), at 35 BTUH per SF maximum, that is 33,600 BTUH heat load available for you. That should be easily within reach of the smallest wood boiler. Thus you MAY want to consider, if the heat loss is higher, getting some panel radiators in there for spot use. At least have some valves at the ready so you can add them without a fuss.



The good news is, radiant floor heat "cheats" the way your body feels about comfort. In other words, because you are bathed in radiant heat, the building can be a bit cooler than you normally would set for comfort. If you like 68-70 in your house, 64-66 may well work just fine in a radiant heated building. Not an absolute, but in general.



The pressurization question: The brazed plate heat exchanger that Ironman mentioned is as much to isolate "open to atmosphere" (your wood boiler) from what should be a closed, oxygen-free system. Yes, your outside boiler has some pressure but at its least, it has zero, that of the atmosphere.  Your indoor (pressurized) circuit will be about 8-12 psi at rest and may rise to 15-20 when hot. (Lots of variables here, but you get the idea, this is an isolated beast.)



Post a sketch if you can of the basic layout, where windows, doors and stationary features are, (where the tubing will enter the slab, too), and I can generate a plan for you to chew on. (Or look at.).

Ironman

Plate Heat Exchanger...

As Brad pointed out, the plate heat ex. is necessary for hydraulic isolation, i.e. a non-pressurized circuit on one side and a pressurized on the other.



A circulator does not create pressure in a closed system; it only creates a small pressure differential between supply and return to induce flow in the circuit.



The link was to show one means of controlling temp in the radiant loop, in this case using a variable speed injection control with outdoor reset.

Tracey

Arrgh! I did it again...

Scrolled the page up then hit backspace, boom reply gone.... Wish I had a cat to blame it on...LOL



No advil, but I do have ibuprofen! Why not is good. That's usually my philosophy also!



Infiltration, (that's another new word for me. See, I'm learning!), will be a big factor for my building, but not as big as most pole buildings I'd say. The ceiling has metal sheathing attached to the bottom of the roof trusses. It is similar to the exterior tin except it is a thicker gauge metal with taller ridges so it will support the weight of insulation. The spray in urethane would be great but I'm guessing the cost will put a damper on that. Fiberglass batts or blow in will probably be what it gets.



Yea, 960 sq ft is what I stated, but you are correct in thinking it will differ from that. The building was originally 30' x 32' with 10' eve height. A few years ago I had to move one of the side walls in 6" on one end, 3" on the other. That's a long story, but lets just say unfortunately my neighbor is still breathing...



Take into account the thickness of the walls, my relocated wall, the roll up and entrance doors, and my "bathtub" looses about 60 sq ft. Total wall thickness will be 5-3/4". Interior height is 9' 4". I'll see what I can come up with for a sketch. I can draw it on paper easy enough, but on the computer that's another ball game! Maybe I can talk out scanner into a little cooperation and just use paper.



Is 35 BTUH per sq ft a good average number? Considering your 33,600 BTUH heat load I'd guess double that at least... LOL The heat exchanger coil I have in there now is rated at 125,000 btu if I remember right. But I do have alot of infiltration at the base of the walls and no ceiling insulation as stated above. I left the base of the walls unfinished on the inside due to not knowing how I was going to do the concrete. I'm hoping the XPS and concrete will eliminate that infiltration source.



Pressurization... I'm struggling with this. Not how, but why. My current system pumps, (circulates), water through pex tubing in the ground to the heat exchangers in the house and shop without pressurizing the system. Why is pex tubing in concrete any different than what I have now. (I still haven't completely read the links you guys provided so bear with me if the answer is in there. I'll get there I promise).



The only thing that's coming to my mind as to why I would need to isolate one system from the other is due to the mixing valve and multiple loops to get a uniform flow for each loop? 



Also my current system uses no anti freeze of any kind. Just straight water with some sort of additive to get a specified Ph level. I'll have to dig out my Pex to see if it o2 barrier or not. I bought it a few years ago and it's just laying around...patiently waiting... LOL



RobbieDo, Nope, my heat exchangers are copper tubing looped back and forth through aluminum fins that just fit into the forced air furnace duct plenum. No plate exchanger.



My boiler is a Central Boiler Classic 5648 (It's current equivalent model is a 6048). Rated at 500,000 BTU max. House heat exchanger is a 60,000 BTU unit and the shop has a 125,000 BTU. Both seperate systems, (other than the boiler), each with their own Taco brand pump. I forgot to mention the boiler also heats our hot water with a simple double wall single pass copper tubing heat exchanger. Our electric hot water heater has been shut off all winter and we haven't ran out of hot water yet!







Robbiedo

NRT_Rob

outdoor boiler MFGs

often cut many corners to get the apparent cost of their boilers down. they go unpressurized, and advocate for unpressurized heating systems. However, there are several issues they introduce there:



-the need to treat the water with anticorrosive substances (money, maintenance),

-lots of potential air problems in many systems (because of unpressurization)

-High parasitic electrical draw from constant circulation pumping



and they do this to keep the boiler cheap. If only they would fit the boiler with a plate heat exchanger!!



That said, if you are doing a single level heating system and all of the heating system is below the boiler level, you can do an open unpressurized system and be fairly sure you won't have air problems. any multilevel buildings though and I wouldn't do it. Lots of people around maine get heat exchangers cut in after the fact.



If the water is not maintained perfectly, it can get really skungy which isn't good for the system either.

Tracey

NRT_Rob

Ahh, Another thing I hadn't thought about. Our house is 2 story, but the boiler system is just single level since it just uses the forced air ductwork in the house.



 The additive for the water in our system was about 50 bucks when the boiler was installed. I've never had to add any more and they recommend testing it once a year. (I haven't done that this year yet. Now that it's been brought up I need to do it.) The test kit came with the boiler and is rather simple. The tests Ph level and nitrite now that I looked at the kit.



The pumps are very low electrical draw if I remeber right but I could be wrong. I can't find the wattage requirements right at the moment (My pumps are Taco 007.)



I'm a firm believer in the K.I.S.S. principle. If you're unfamaliar with that it it's Keep It Simple Stupid. (Don't take that personally...LOL) Everything added to any system is something else to go wrong. If you've ever worked on an old car and a modern one you would know exactly what I'm talking about! I envision more problems with a pressurized system than an unpressurized system.

More initial cost, more stress on the pex tubing and other parts.



I can see the need to pressurize the system to assist in bleeding air bubbles when first installed, but after that...?



Just from looking at plate heat exchangers on ebay last night I can see that a presurized system is definately higher priced. I would need some sort of expansion tank also in a pressurized system?



So since my radiant system is below the level of the boiler I shouldn't need the plate exchanger and pressurized system, correct?

NRT_Rob

if it's laid out properly

and lower than the boiler you'll probably be fine. doesn't sound like you're really anal about maintenance though so that is a concern.... it's a much bigger issue with open systems than with closed systems.



007's are not "low draw" but they are lower than what many people are using. Still, that's easily $10/mo in electricity in most areas or even more. You can ballpark it at a quarter a day per ten cents/kwh price tag on your power for that pump.



components in a closed system will typically outlast components in an open system.



further, if you have to glycol for any reason you can. say you have to leave town for a month because of a sick relative or something.

Tracey

Thank god I'm not

anal! Hahaha How did anal become a good thing anyway....?? LOL



That's good news to me! (no pressurization needed) The way I'm looking at it componenets may last longer in a pressurized system but there are more componenets to go bad. Sick relatives are just going to have to go to the doc...Glycol ain't happenin! LOL The boiler itself holds 385 gal of water, plus whatever is in the rest of the system. To glycol it would cost as much as the system did to begin with.

For the radiant part of the system I will plumb in some way of isolating it from the other part for maintainence. (Changing a pump, changing a valve, and possible glycol if an emergency did arrise). I think that would be pretty much standard procedure though?



Speakin of glycol, I know there is a specific kind used for these systems What's it's first name?



Still lookin for my drawings Brad... I know they are here somewhere... Headin out to check what kind of Pex I have now. It will be labeled on the tubing itself I hope? Is o2 barrier still needed in an unpressurized system?

NRT_Rob

obviously

if you were going to glycol you would want a heat exchanger, that is why I mention it in the plus column for heat exchangers. You never know when life will strike, and basically closed systems can let someone do anything they need to do with confidence.



open systems, much messier that way.



Certainly put in an isolation point and leave room to cut in a heat exchanger should it prove necessary.



the glycol that would be used, if necessary is inhibited propylene glycol.