DIY Hydronic Floor Heating

[Drake]

Radiant installers/designers seem to vary greatly on pex size, even residential, from 3/8" for small area to 7/8" and every one seems to have a reasonable theory why their way is best. It is hard to sort out. Larger tube, longer loop, wider spacing vs smaller tube, shorter loops, closer spacing. Even in mass slab floors.

[berniebenz]

Originally Posted by Drake

Can different diameter pex be run off the same manifold if each loop has near equal flow resistance? Are there numbers for # of feet of various dia tubing for flow resistance? Like ?' of 1/2" is same as ?' of 3/4". Would the flow restriction of a max 1/2" loop be same as max 3/4" loop?

Q1: Sure, it can be done, but not suitable for in floor heating.

All parallel loops driven from a pressurized manifold, regardless of diameter and length will experience the same overall pressure drop. The flow through each loop will differ, dependent upon the length, diameter, and surface friction characteristics of the loop material. With equal loop spacing on the floor, the design objective is to achieve uniform heat loss, transfer per unit loop length. Why a simple design uses similar materials excepting for unavoidable slight differences in loop lengths. Why a good manifold will have a throttling valve in each loop to compensate for differing, shorter loop lengths.

[michael]

[QUOTE=AC_Hacker;29159I'd be interested to know what your loop spacing is, and I'd also like to know if your loop is all one circuit, or if it's composed of parallel branches. You did mention that there was a slab involved. Since you didn't indicate otherwise, I assume that your slab in on the ground. Is there any insulation under the slab? If yes, how much? Do you have any information about the insulation in your house? Walls? Ceiling? Window configuration? Single glass? Double or even triple glass? I did a Heating Degree Day check. Ukiah was the closest I could find, and your average HDD is 4886.
-AC[/QUOTE]

Hello AC...I can try to answer most of those. Our loop spacing is 6". In general, they are spiral loops running in and out next to each other 6" apart, and all loops are 200' long. The loops parallel each other for several feet right after they enter the floor area from the manifolds, but then they divide off and spiral. The pipes are in 1.5" of concrete on top of plywood with R-19 below in the crawl space. My son poured a similar floor except it is slab on grade with a foil backed air pocketed insulation below. Our house has R-30 + R-19 in the ceiling and R-19 in the walls. We have all double glazed windows, and they comprise about 400 square feet including doors, but the windows have a low U value because they have a very narrow internal space. The 4886 degree day figure is what I found for a 65 degree balance point, but it shoots up to 6200 for a 70 degree balance point. One final thing about the radiant system, there are ten loops, but one zone. The whole deal is controlled by one thermostat. There is no heat in the bedrooms.

[Mikesolar]

Originally Posted by Drake

Radiant installers/designers seem to vary greatly on pex size, even residential, from 3/8" for small area to 7/8" and every one seems to have a reasonable theory why their way is best. It is hard to sort out. Larger tube, longer loop, wider spacing vs smaller tube, shorter loops, closer spacing. Even in mass slab floors.

A 3/8" tube will be closer to 1/2" OD and a 1/2" is about 5/8" OD

[AC_Hacker]

Originally Posted by Drake

Radiant installers/designers seem to vary greatly on pex size, even residential, from 3/8" for small area to 7/8" and every one seems to have a reasonable theory why their way is best. It is hard to sort out. Larger tube, longer loop, wider spacing vs smaller tube, shorter loops, closer spacing. Even in mass slab floors.

Drake,

You might be asking technical questions that are beyond the limits of knowledge of anyone here to answer you properly.

Since you do have college degrees in art and science, as you stated in a previous entry, you should be able to get some of these answers yourself.

My recommendation to someone as educated and resourceful as yourself would be to obtain this free radiant heating simulation program called RadiantWorks from Watts Radiant.

Once you install it on your computer, you can go through the entire design process which consists of entering the design temperature for your area (it has data built in) enter the specific information for your building, go into detailed description regarding the various options available to you for heating, and look at the output.

Then start modifying the layout, change the pipe diameter, change the layout, change the floor covering. See for your self what difference these things make to a radiant heating system. Before you know it, you will have a real system-understanding of how it all works together.

Then you will be in a position to answer these questions, from a keen basis of understanding, for yourself and others.

Sincerely,

-AC

[Drake]

Thank you AC for the direction. One never knows what answer one may get to a question until it is asked and one never knows to whom it may being asked on the open internet. Regrettably I am of the Mac world and the Radiantworks software doesn't look compatible but will look for someone I may know w/Windows that might let install it.

One the most important things I learned from education is that very little knowledge is absolute and that there is a very real difference between theoretical knowledge and applied knowledge. Experts of theory are not often the best source of innovative ideas. On the five radiant install companies I have inquired with so far only two have agreed on the "best" size pex let alone at what level to place it in concrete. I greatly appreciate the input from those that have working systems being used(or nonworking and why) as a real world balance.

[berniebenz]

Originally Posted by michael

but the windows have a low U value because they have a very narrow internal space. .

The heat loss of double glazed vertical lites is the combination of conductive and convection losses. The optimum being ½” to ⅝” spacing for minimum heat loss.

[Mikesolar]

Originally Posted by Drake

Thank you AC for the direction. One never knows what answer one may get to a question until it is asked and one never knows to whom it may being asked on the open internet. Regrettably I am of the Mac world and the Radiantworks software doesn't look compatible but will look for someone I may know w/Windows that might let install it.

One the most important things I learned from education is that very little knowledge is absolute and that there is a very real difference between theoretical knowledge and applied knowledge. Experts of theory are not often the best source of innovative ideas. On the five radiant install companies I have inquired with so far only two have agreed on the "best" size pex let alone at what level to place it in concrete. I greatly appreciate the input from those that have working systems being used(or nonworking and why) as a real world balance.

1/2" nominal (5/8" OD) O2 barrier tube is what you need. It is used for 99% of residential floor heating system. In a slab with 250' lengths, 9" spacing and good XPS under the slab, you can easily get 35btu/ft with a dT of 20F. Depth in the slab is debated quite a bit but my practice is to keep it at the bottom especially if the slab is not going to have a big setbacks at night. Having the tube at the bottom gives a more even surface temp.

[AC_Hacker]

Originally Posted by Drake

...One never knows what answer one may get to a question until it is asked...

You might include the string "John Seigenthaler" in your queries to the open web regarding the more arcane aspects of radiant heating.

On the 'tube placement' issue, he has done some really interesting finite element analyses you'd be interested in.

-AC

[cbearden]

Originally Posted by Drake

Thank you AC for the direction. One never knows what answer one may get to a question until it is asked and one never knows to whom it may being asked on the open internet. Regrettably I am of the Mac world and the Radiantworks software doesn't look compatible but will look for someone I may know w/Windows that might let install it.

One the most important things I learned from education is that very little knowledge is absolute and that there is a very real difference between theoretical knowledge and applied knowledge. Experts of theory are not often the best source of innovative ideas. On the five radiant install companies I have inquired with so far only two have agreed on the "best" size pex let alone at what level to place it in concrete. I greatly appreciate the input from those that have working systems being used(or nonworking and why) as a real world balance.

Drake,
Why not install Virtualbox on your mac, setup a trial or a 2nd-hand copy of windows, and then you can run whatever software you like on it?
That's what I did with my radiant software, LoopCAD. I ran it in a virtual machine under Win XP, and rolled the date back on my machine so I could keep running the cad software in its trial mode.
VirtualBox download (for mac too):
https://www.virtualbox.org/wiki/Downloads

Windows 8 trial download:
http://msdn.microsoft.com/en-us/eval.../jj554510.aspx

It would take a little work to setup, but if all you need is something temporary and free, then you can't beat it.