In-Floor Heat Questions

[jeff5295]

I would not even bother hooking that setup into your system!

You need to STOP and insulate. Then install 2-3x as much radiant tubing. You only get one shot at doing this right. Honestly, whoever did that does not know what they are doing and is just taking your money for shoddy work.

Tim

Tim, If I understand the thread, this isn't his system, but one that a builder did in his area for example.

You definately do not want that guy doing your floor.

I can't believe he would actually share that picture with you. It just proves that he either truly knows nothing about radiant heat, or he believes that you know absolutely nothing and can B.S. you into thinking this is proper. Don't let him fool you into using the "bubble wrap" foil insulation either. It's worthless under a slab. You absolutely need some type of high density foam insulation or don't even bother putting the tubing in.

Do a little research to educate yourself. There's plenty of websites with great info on the subject. That's how I figured mine out. It's not rocket science, but there are a few basic laws that need to be followed or you're wasting your time.

I don't recall the websites I used, but I'm sure others can chime in with some links.

Do yourself a favor and get rid of this "contractor".

 

[jeff5295]

Do yourself a favor and get rid of this "contractor".

Sorry, that may be a bit harsh. Maybe he's a great builder, but just doesn't understand radiant heat. You either need to educate yourself to know you're getting what you need or possibly hire an experienced radiant heat installer to handle this portion of the build. It's quite obvious he doesn't quite know what he's doing. It's actually really easy. I've done two systems myself. If you've got questions I or someone else should be able to assist.

 

[GSSFC]

Sorry, that may be a bit harsh. Maybe he's a great builder, but just doesn't understand radiant heat. You either need to educate yourself to know you're getting what you need or possibly hire an experienced radiant heat installer to handle this portion of the build. It's quite obvious he doesn't quite know what he's doing. It's actually really easy. I've done two systems myself. If you've got questions I or someone else should be able to assist.

That is why subs are important. One contractor simply cannot know how to correctly do every phase of the job correctly. You need specialists in each category. There is so much more to building SCIENCE than just nailing boards together.

Tim

 

[livetohunt]

Thanks for all of your help, guys. Just to clarify a few things:

1. The picture I posted was sent to me by a fellow homeowner in our neighborhood who built a couple of years ago. I called him and asked how his floor heat worked, without having insulation under the tubing. He told me that he is very satisfied, and offered to send me some pictures. So the picture is of his house, not mine. I wanted to show you how they have done it in the past in our neighborhood.

2. It is our builders opinion that floor heat does not require insulation. It is our plumbers opinion that we should use "Slabshield", or at a minimum the 2" high density sheets.

3. The plumber who is doing our install is not the same plumber who did the work in the picture that I posted.

4. Based on your answers, research that I did on the internet, and talking with others, I have informed our builder that we will be using the pink 2" high density sheets of insulation under the pex, and on top of the vapor barrier.

5. Our floor heat installation has not begun yet, so if they use 1/2", how close should the loops be to eachother? How about 3/4"?

Thank you again, this has been a very informative discussion and has helped solidify my decision to use the insuluation.

Thanks!!

 

[livetohunt]

I would not even bother hooking that setup into your system!

You need to STOP and insulate. Then install 2-3x as much radiant tubing. You only get one shot at doing this right. Honestly, whoever did that does not know what they are doing and is just taking your money for shoddy work.

Tim

This is not our house, it is a picture that was sent to me by a homeowner in our neighborhood. We are using a different installer for our house

Is there a spec for how many feet of tubing should be used? Our basement is 1500 sq feet.

Thanks!

 

[havi]

My floor is 44x36, or 1584 SQ FT. I have 5 pair of tubes coming out of the floor. But looking at my pic, it's hard to tell which zones are which. Each "row" is a straight line one way, and half-circles the other, with two rows facing each other. Not sure if that helps any. I should mention there are no room specific zones.

 

[tdkkart]

5. Our floor heat installation has not begun yet, so if they use 1/2", how close should the loops be to eachother? How about 3/4"?
Thanks!!

Based on the information I gathered before doing my shop, for 1/2" tube I would go 12" intervals, slightly wider for 3/4" tube.

You said you had a wall that was only going to be 2ft into the ground?? This will be your highest heat loss area, so along that wall I would put the first 3-4tubes in 6" apart, then start your 12" spacing.
Use however many loops it takes to stay within the 300'/loop rule.

 

[nate379]

I have roughly 12" spacing on my tubes. The tubes are 5/8" I belive and the ones that run to manifolds on the back side of the house are 3/4"

 

[tdkkart]

See this thread for info and pics on my recent shop floor project:
http://www.garagejournal.com/forum/showthread.php?t=34473

 

[livetohunt]

Use however many loops it takes to stay within the 300'/loop rule.

Can you explain that a little more? What is the rule in laymans terms?

 

[nate379]

The run of pex shouldn't be more than 300ft.

Run several runs if you need more coverage. Like in my 24x26 garage I have 3 loops.

 

[tdkkart]

Can you explain that a little more? What is the rule in laymans terms?

Rule of thumb for 1/2" tubing is that you should not have more than 300' of tubing for each loop.

A couple reasons for this.
1. The longer the run, the more "head" pressure the pump sees. Using a reasonable size pump 300' is the max you can run before running into trouble with pressure. You can use a bigger pump to push more water, but bigger pumps are more expensive, cost more to operate, and take up more space. "Standard" heating system pumps sort of dictate the 300' rule.

2. The longer the run, the more heat you draw out of each loop. Most systems are designed to drop approx. 15-20* of temperature out of the water as it flows through the system, any more than this and you risk having a hot spot on one end of the loop and a cold area on the other end.

If you read through my thread above you will find that I used 850' of tubing
for a 24x30' area, or approx. 1.2ft of tube for each square ft of floor.
The tubing is in 4 loops, so I used approx. 212ft/loop.

Take a look at this manual, study it and it will answer alot of your questions:
http://zurn.com/images/pdf/ZPM02101.pdf

 

[ScaldedDog]

Here's a photo of mine with 1/2 tube. I wanted 9" between the runs, but that turned out to be a pain when tying it to 6" mesh. I opted instead for some 12" spacing and some 6" spacing. Not a great idea in a house floor where you notice and will care about hot spots, but fine for a garage, IMHO.

Mark

 

[GearBeer]

Radiantec has some information for the length and spacing of runs of different diameter PEX. I do not know how accurate their information is, but most of the people I have consulted agree with it. *shrug*

To opine on the foil and air or foil and foam insulation versus the conventional foam board discussion:

You should consider the principles of heat transfer that are occuring here. Heat will be transferred to the ground from the slab by conduction. Conductive heat transfer is a function of the thermal resistance of the insulating material and the thickness of the insulating material. Therefore, thicker sheets of insulation with higher thermal resistance will impede the heat transfer better than thinner, reflective sheets.

These reflective insulation produts are probably not a very effective form of insulation in this application. Consider that radiation requires a medium (air) with a high transparency. Therefore, there is very, very little radiation through concrete and the high reflectivity of these products is wasted.

 

[redsky49]

Thanks for all of your help, guys. Just to clarify a few things:

1. The picture I posted was sent to me by a fellow homeowner in our neighborhood who built a couple of years ago. I called him and asked how his floor heat worked, without having insulation under the tubing. He told me that he is very satisfied, and offered to send me some pictures. So the picture is of his house, not mine. I wanted to show you how they have done it in the past in our neighborhood.

2. It is our builders opinion that floor heat does not require insulation. It is our plumbers opinion that we should use "Slabshield", or at a minimum the 2" high density sheets.

3. The plumber who is doing our install is not the same plumber who did the work in the picture that I posted.

4. Based on your answers, research that I did on the internet, and talking with others, I have informed our builder that we will be using the pink 2" high density sheets of insulation under the pex, and on top of the vapor barrier.

5. Our floor heat installation has not begun yet, so if they use 1/2", how close should the loops be to eachother? How about 3/4"?

Thank you again, this has been a very informative discussion and has helped solidify my decision to use the insuluation.

Thanks!!

Holy cow! The blind leading the blind.

Spacing of the tubing is based on:
Flow rate of heating fluid (tubing size is a result of this requirement, not the other way around)
Temperature and specific gravity of heating fluid
Design temperatures, indoor and outdoor
Insulation values
Etc.

There is no "rule of thumb" for hydronic systems. No way, no how! Btu requirements are what drives the layout. You cannot "ball park" these systems. They must be sized, by an experienced, knowledgeable designer to each particular installation. Each project is essentially a prototype, with its own individual needs and requirements. In some cases this designer will be a Contractor. In other cases a Vendor or an Engineer. In any case, if you want to be successful, get a professional opinion.

Some of the opinions posted here are simply wrong. Don't be penny wise and pound foolish. If nothing else, at least get a professional to sign off on what you intend to install. My hard-earned cash is too precious to gamble on a heating system that you will have to live with for years to come. I suspect that this applies to the OP as well.

Do it once. Do it right.

As always, offered only as opinion

 

[livetohunt]

UPDATE

Thanks for all of the info. I met with the builder & HVAC installer, and I insisted that we use insulation. So here is the stack of insulation sheets that is onsite & waiting to be installed. 2" thick sheets of high density foam.

 

[kvom]

I used 5/8" Pex in my floor, and it's difficult to bend as tightly as 1/2". That said, my system works really well. We are in a much milder climate zone. Were I to do another I would use 1/2" PEX and run more loops, esp. in a cold climate.

 

[livetohunt]

Insulation is down and tubing went in today. Thanks again for all of the advice on insulation