# Hydronic radiant heating spacing ?



## Joasis (Mar 28, 2006)

I haven't poured the concrete yet, weather issues, but w have laid the lines, and as noted above, 1 foot spacing at the perimeter, and then 18 inches in...the point being that concrete 6 inches thick will warm pretty evenly, over time. 

The only concern to me with a longer loop, is simply head pressure. The idea that the temps will drop too much in a longer loop will not be a factor as the floor comes to temp. Also....in zoning, if one pump runs the entire system, and mixing valves/manifolds direct the flow through shorter loops, it would seem the same thing as a long loop. 

Anyway, next winter will be the first trial. But, there will be no ripping it out.


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## The Coastal Craftsman (Jun 29, 2009)

dakzaag said:


> No plumber will tell you this, but in concrete you can space 18" on the inside runs. A couple of outside loops at 8-12" and your good. The concrete will evenly heat over time, about a week for my 1600 sq. ft. basement. Once it is up to temp, the pump for the basement runs about 1/3 the time of the upstairs. Think of the slab as a big radiator, we go downstairs to warm up from outside.
> 
> I agree with the 300 ft. length. Temp drop is too much on a longer loop. Seperate zones for every room in the house is pretty much a joke as far as I am concerned. I honestly think if I had one zone upstairs and one downstairs, I would be fine. I put in 5 zones upstairs and 3 downstairs and played with the valves, but never really made any difference. I did however maintain a 325 foot max loop, thats why I ended up with 5 loops. Also upstairs the spacing is more like 9".
> 
> ...


 
You are wrong on quite a few things here. Like i said i have fitted maybe 40-50 underfloor heating systems on rooms from 100sqft to houses that are 5000sqft+ the 18" spacing is way to much under any circumstance. The largest centers we ever had were no more than 10" and that was because of being in areas where the pipe had to make a large radius turn to meet the drawings design. Like loneframer also says you should have even closer spacing on external walls also. some of these are as close as 4" depending on construction of walls. I have also done rooms that have had as many as 5 separate zones which all have there own stat under the floor that run to a central room stat. It's not uncommon at all to see this. Infact it has to be done so that the zones can be balanced if there's more than one zone in each room. 

But i have seen it put down like you say and it give a very uneven slow heat recovery. A underfloor heating system done correctly should heat up from cold in about 20-30 mins and give a even heat around every room with zero hot spots.


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## dakzaag (Jan 6, 2009)

I agree that as the slab temp reaches your set point, the longer loop will be less of a factor. I think the longer loop may require more time to get there, but I am not sure how much longer. 

An additional concern I had in the concrete was if there was a line failure, repair would be a major issue. Several shorter loops can allow the system to still function by abandoning the failed loop. Obviously the bigger the area a loop covers, the less likely the system can compensate for a failed loop. I have seen some systems in concrete that alternate the loops every other coil so that a failure will still allow the system to function.

Head pressure really shouldn't be an issue as you want the water to travel slow enough to transfer the heat before it returns to the boiler. In this area, your longer loops will most likely have an advantage of more time to transfer heat. 

I have an intermediate loop that circulates water from the boiler to my secondary pumps and a heat exchanger in my forced air system. The upstairs and downstairs pumps take water from the initial loop and feed the secondary loops through out the house. After the secondary pumps, the manifolds are mounted to allow zone control. 

Like I said earlier, after the initial setting, I haven't touched the manifolds for 8 years. How many pumps you install really determine how much control you have. I can control my upstairs and downstairs seperately and also the back up forced air can in theory run independently although it is designed as a secondary source, if the radiant falls behind.


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## The Coastal Craftsman (Jun 29, 2009)

joasis said:


> I haven't poured the concrete yet, weather issues, but w have laid the lines, and as noted above, 1 foot spacing at the perimeter, and then 18 inches in...the point being that concrete 6 inches thick will warm pretty evenly, over time.
> 
> The only concern to me with a longer loop, is simply head pressure. The idea that the temps will drop too much in a longer loop will not be a factor as the floor comes to temp. Also....in zoning, if one pump runs the entire system, and mixing valves/manifolds direct the flow through shorter loops, it would seem the same thing as a long loop.
> 
> Anyway, next winter will be the first trial. But, there will be no ripping it out.


 
You would be surprised at how much pressure drop there is on longer runs. There's a few reasons to try and keep lenght runs as close as possible. It helps the system to be more balanced which is very important. Even though you should have flow meters on every valve on each manifold and adjust to suit, it's best to keep runs on the shorter side, mainly because of recovery time and even heat distribution.


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## Joasis (Mar 28, 2006)

There are multiple factors that determine what will work, for any given climate, and for any given material. 

For instance, 6 inches of concrete on sand. Soil temps constant at 64 degrees when shielded, and temperature of water. The volume of the pump, and the drop of temps after one pass.....lots of factors.

For anyone to say what will or will not work, in every given environment, is ludicrous. 

BTW dakzaag, as this is not a primary system, if a loop fails, then it isn't a big deal. Kind of like running a 1000 foot loop in the garage...if it keeps the vehicles warmed up during the coldest months, all good.


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## The Coastal Craftsman (Jun 29, 2009)

joasis said:


> There are multiple factors that determine what will work, for any given climate, and for any given material.
> 
> For instance, 6 inches of concrete on sand. Soil temps constant at 64 degrees when shielded, and temperature of water. The volume of the pump, and the drop of temps after one pass.....lots of factors.
> 
> ...


 

Thats the whole reason to have a proper company and who do all the tests they do. I have not had one system under or overheat an area in all them installs. The thing is dont cost anything to get the company to come out and size the system. I have installed on almost every different soil base in the UK. Mostly clay though. Im not sure if that make any difference but between the clay and the concrete there would be 6-10" of insulation then after the concrete another 2-3" of insulation then the grid and then the screed. Soil temps didnt really play a part in sizeing the systems. Some of the block and beam floors took into account the fllor type though.

But like i said those centers sound far far to big no matter where the system is installed. You will get slow uneven heat distribution without a doubt in my mind. The system will also cost you far more to run than it should if correctly installed. Just as a example do a goggle search for images on underfloor heating. You will see the normal ranges of centers are anything from 2-10" with 10 being pretty uncommon and for houses with exceptionally high r values.


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## beenthere (Mar 5, 2009)

joasis said:


> There are multiple factors that determine what will work, for any given climate, and for any given material.
> 
> For instance, 6 inches of concrete on sand. Soil temps constant at 64 degrees when shielded, and temperature of water. The volume of the pump, and the drop of temps after one pass.....lots of factors.
> 
> ...


People that increase center distance on the interior loops often need a secondary heating system. Or use hydro coils in the air handlers.

Its also a reason why many in floor radiant systems don't respond well to outdoor temp changes. They can't because they are short on loop length.

Hope you are using floor temp sensors.

If it takes a week to heat up a 6" slab.
You either don't have it insulated, or you don't have enough pex installed.
Or, you had a heating system failure for a few days and the house temp drop to 40°.


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## TimNJ (Sep 7, 2005)

Make sure that slab is up and away from any ground water. My first floor is slab and I put 5-6" 3/4 clean stone then 4" of styrofoam, then poured my slab 4"-5". If the bottom of your slab comes in contact with water it will never heat up. Those long lengths are going to drop the water temp by the time the water gets to the other end. I had to raise my water temp to compensate for the larger spacing. Instead of the design temp of 120 I am operating it at 135 and maintaining the 20 deg delta T. 
I would rather have extra tubing in my slab and either not use a loop or two or run the system at a lower water temp than not have enough tube and having to run at a higher temp. Once the floor is poured your screwed.


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## beenthere (Mar 5, 2009)

TimNJ said:


> Those long lengths are going to drop the water temp by the time the water gets to the other end. I had to raise my water temp to compensate for the larger spacing. Instead of the design temp of 120 I am operating it at 135 and maintaining the 20 deg delta T.



How long are your loops, and what circ are you using for what flow rate.


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## TK03 (Feb 2, 2009)

1000 ft loop?????? Never work much less be comfortable. If you get the flow you need it will be noisy and the delta-T is going to be ridiculous. The comfort thing can be overcome with auto reverse flow. Run one direction for awhile then got the other direction. The flow is going to take a honken big pump.


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## TimNJ (Sep 7, 2005)

beenthere said:


> How long are your loops, and what circ are you using for what flow rate.


The longest loop is 175'. I have it in two zones, one with 5 loops and one with 4. One zone carpet and one zone ceramic. The boiler is piped primary/secondary. Each zone has its own circulator. The 5 loop zone has a Taco 0011. Heatway had me switch to this pump when I was dealing with their staff. This is a noisy pump. When I changed it it made no difference from the 007 that was there originally. I just kept it in place since it cost so much:furious: Everything else is Taco 007 (primary boiler loop and pump for radiant zone. The 4 loop zone gets its hot water source through a Boilermate and the 5 loop zone gets its hot water source directly from the boiler with a mixing valve piped in. Someday I would like to put the 5 loop zone on a Boilermate too. Aside from the ease of setting the water temp to the slab, that zone seems to respond faster since when the stat calls for heat I have 40 gal of preheated water pumped right out on demand. If the boiler has been off for a while the other zone has to wait for the boiler water to heat up first.
Not sure what my flow rates are. I have large file with all the info on flows for different size tubing, BTU's per ft for different size tubing. I did a lot of research when I repiped everything and since I don't do this for a living everyday it gets put in a file and stored away for future reference ... if I can ever find it again


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## Joasis (Mar 28, 2006)

TK03 said:


> 1000 ft loop?????? Never work much less be comfortable. If you get the flow you need it will be noisy and the delta-T is going to be ridiculous. The comfort thing can be overcome with auto reverse flow. Run one direction for awhile then got the other direction. The flow is going to take a honken big pump.


Several years ago, we did a large shop, done the same way, 1/2 inch pex, 18 inch average spacing, 6 inch floor. 5000 sq/ft, all loops continuous, and a commercial water heater for a boiler. It works, and works fine, says the owner. 

This ain't rocket science guys, and this is not a primary system for me. I don't doubt that many of you have a lot of expertise in hydronic systems, but what I am doing is not in the book, and will work. How well is not that important, but again, we are not flying the space shuttle.


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## beenthere (Mar 5, 2009)

joasis said:


> Several years ago, we did a large shop, done the same way, 1/2 inch pex, 18 inch average spacing, 6 inch floor. 5000 sq/ft, all loops continuous, and a commercial water heater for a boiler. It works, and works fine, says the owner.
> 
> If it isn't costing him a lot to heat with. But the shop is cold and his office is warm. An owner will say it works fine. Even though the people in teh shop are cold.
> 
> This ain't rocket science guys, and this is not a primary system for me. I don't doubt that many of you have a lot of expertise in hydronic systems, but what I am doing is not in the book, and will work. How well is not that important, but again, we are not flying the space shuttle.


I would think how well it really works is important. If your giving info/instructions to other people on how to do it.


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## beenthere (Mar 5, 2009)

TimNJ said:


> The longest loop is 175'. I have it in two zones, one with 5 loops and one with 4. One zone carpet and one zone ceramic. The boiler is piped primary/secondary. Each zone has its own circulator. The 5 loop zone has a Taco 0011.


What size pex did you run.
How many GPM is a is the longest loop suppose to move?
Is it 100% water, or do you have glycol added?


Thats a lot of circulator.


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## Joasis (Mar 28, 2006)

beenthere said:


> I would think how well it really works is important. If your giving info/instructions to other people on how to do it.


I am not giving instructions to others, I was seeking a few opinions for thought. 

Lets do some calcs. 

1/2 inch pex will have a volume of .92 gallons per hundred feet, right? 1000 feet, 9.2 gallons in the loop. 

OK so far? 

Now...lets assume a solar panel with a pass rate of 10 degrees, which is what we go in the dead of winter on a solar greenhouse many years ago, 4 - 4x10 foot vinyl panels.....in parallel, probably higher in series. 

The basic I am working on is simple. When the water out of the collector is say 100 degrees, pump kicks on. When the water out drops below that value, pump off. If the floor temp reaches 85 degrees, pump off. No auxiliary heat source or boiler...strictly solar. Drain back system. 

Now...14 GPM pump, panels 9 feet above the floor line. The only interest I have is the head pressure from the length of the loop. I know it will heat, I know it may be slow, but, it fits what I am doing. Oklahoma is not a northern climate, soil temps are higher, and if the floor gains heat to 80 degrees, great. If not, I am out a little time and a few bucks for pex. 

BTW guys, just one room in my new home is 1080 feet...and it has one 1000 foot loop. The garage is a shade over 2000 feet and earth sheltered to the north. Another 1000 foot loop, and finally, another 1000 feet divided between the kitchen, den, master bedroom. I hope this makes a little more sense, but it is what it is. The tubing is laid, and all I need is a few warm days and the floor willbe poured, changes locked out. :thumbsup:


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## beenthere (Mar 5, 2009)

Head from length of loop, and the solar panels.
What GPM per loop. Hope not 14 per loop.

Your going to need a big circ. And you'll have some noise.

Should have been ¾" pex for that long of a loop. But 5/8 could work, depending on GPM needed per loop.


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## 747 (Jan 21, 2005)

There are all kinds of factors which go into this. Everything from windows to insulation to room size to geo location of home.. Basically there is a computer program where you input the data and it makes the determination for you. Basically you just bring in a guy with his laptop and inputs the data into the programs fields.

I think it looks good in the pic. Push comes to shove you can just increase water temp.


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## Griffino (Dec 3, 2007)

Key information I abide by and have been succesful in each application:

1. 250' loop length (1000/4 loops = economy)
2. closer the spacing, the better. 6" for hard surface, 9" for carpet.
3. have a professional specify a pump for your system req.
4. no couplers in your loops.
5. never use in-floor hydronic under a subfloor without heat spreaders.
6. Closely spaced lines under windows and entry doors.
7. extra close spacing in bathrooms and under tubs.
8. stay clear of toilet wax rings, 12" should suffice.

Let me explain why "closer is better". Tubing is cheap, screwing up a job and neglecting return business is not. Widely spaced loops force you to turn up the water temp in the lines, this limits system efficiency and could damage some hard surface flooring products. Also, widely spaced loops will give you a noticeable difference in floor temps, (even with carpet) this matters a lot to the HO. You will get called on this in the future.


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## beenthere (Mar 5, 2009)

joasis said:


> Now...14 GPM pump, panels 9 feet above the floor line. The only interest I have is the head pressure from the length of the loop. I know it will heat, I know it may be slow, but, it fits what I am doing. Oklahoma is not a northern climate, soil temps are higher, and if the floor gains heat to 80 degrees, great. If not, I am out a little time and a few bucks for pex.


½" pex with 100% water at 100°F at 1 GPM has a head loss of .0360 per foot.
So 1000X.0360=36 foot of head(15.6PSIG drop).

At 1½ GPM at same temp, it has a head loss of .07443 per foot.
So 1000X.07443=74.43 foot of head(32.26PSIG drop).

At 2 GPM at same temp, it has a head loss of .12467 per foot.
So 1000X .12467=124.67 foot of head(54.03PSIG drop).

At 2 GPM. Depending on your actual/average OC. You'll get between 16 and 20 BTUs an hour per sq ft of exposed floor surface. At a 20° differential at the loop.


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## TimNJ (Sep 7, 2005)

beenthere said:


> What size pex did you run.
> How many GPM is a is the longest loop suppose to move?
> Is it 100% water, or do you have glycol added?
> 
> ...


Like I said that 0011 was a waste of money.Tubing is not pex. It was Heatway's "own" tubing, "entran" was its trade name. Glorified miniature auto radiator hose is what it looks like to me. Goodyear made the hose for Heatway. All water in the system. I don't have flow meters on either of the zones. This was designed almost 20 years ago now. The industry has changed in leaps and bounds as far as what controls are availble now for radiant systems compared to back then. The system was first operational in '96. I repiped everything back in '99 and I had to hunt far and wide for a supplier that could get SpiroVents for me, let alone even heard of the company. A lot has changed since then. I am planning on redoing my floors. I am hoping to grind my slab down a half inch or so lay out new pex, and pour gypcrete over everything and abandon the old "entran".


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