DIY Hydronic Floor Heating

[berniebenz]

Originally Posted by Vlad

Here is my radiant floor project:
As mentioned before I used:

1. 1x2 wood strips
2. Aluminum foil HD 2' wide from Costco
3. Strips are stapled down and top layer of plywood is screwed down to subfloor through wood strips
4. I used Omega shaped aluminum heat distributing plates. They distribute heat and hold Pex tubes suspended from subfloor (omega shape helps holding Pex tubes in place while you install top layer of plywood. This is very critical)
5 Top layer of plywood is painted black from the bottom.

Seems to me like a lot of extra work for little gain. Qs about the details:

1. The ¾” thick strips confine the PEX which is apparently spaced at 1’ intervals. You must have used ¾” ply for the cover floor, thus your system adds 1.5” to the sub floor.
2. What does the Al foil accomplish? Apparently trying to reflect radiant energy upwards. Only works where reflective surface is in contact with air, i.e. the 3/4” wide space directly under the tube, maybe also somewhat from your heat distributing plates across the 1’ span?
3. I don’t understand the “Omega shaped aluminum heat distributing plates“.
Why not just space your PEX closer?
4. Lots of still air in your heat transfer path, a very good insulator! Top ply not much better.
5. 1” or 1.5” of light weight gypsum poured directly on the sub floor would have achieved much higher conductivity to the surface and across the surface with 6” tube spacing, possibly less expensively.

[AC_Hacker]

Originally Posted by berniebenz

3. I don’t understand the “Omega shaped aluminum heat distributing plates“.
Why not just space your PEX closer?

These pix are of a below-subfloor install, but the principle is the same for above-subfloor install...

below-subfloor staple-up


below-subfloor staple-up with aluminum heat spreader plates

It should be pretty clear what the advantage of heat spreader plates actually is.

-AC

[berniebenz]

Originally Posted by AC_Hacker

It should be pretty clear what the advantage of heat spreader plates actually is.

-AC

I didn’t question the possible advantage of heat spreader plates under some circumstances, only the economics of their use relative to obvious alternatives, such as spacing the PEX closer and imbedding it in a better conducting material than air.

[Vlad]

Originally Posted by berniebenz

Seems to me like a lot of extra work for little gain. Qs about the details:

1. The ¾” thick strips confine the PEX which is apparently spaced at 1’ intervals. You must have used ¾” ply for the cover floor, thus your system adds 1.5” to the sub floor.
2. What does the Al foil accomplish? Apparently trying to reflect radiant energy upwards. Only works where reflective surface is in contact with air, i.e. the 3/4” wide space directly under the tube, maybe also somewhat from your heat distributing plates across the 1’ span?
3. I don’t understand the “Omega shaped aluminum heat distributing plates“.
Why not just space your PEX closer?
4. Lots of still air in your heat transfer path, a very good insulator! Top ply not much better.
5. 1” or 1.5” of light weight gypsum poured directly on the sub floor would have achieved much higher conductivity to the surface and across the surface with 6” tube spacing, possibly less expensively.

1. Yes pex is spaced 12" apart. 6" spacing is impossible in my case because it will make pex loops too long. Plywood is 5/8" and not 3/4".

2. Read this first: Physics of Foil: Radiant Barrier Stops Heat Gain & Loss in Buildings

3. Omega shape is a slot or bend shape in aluminum plates. It locks pex tube.
http://www.pexuniverse.com/store/pro...ates-htp122100
http://www.warmfloorcenter.com/heattransferplate.html

4. This is a point to insulate top plywood from subfloor. For this reason I didn't want to fill the gap between loops.

5. I checked concrete / gypsum options. Very expensive in our area. Also I didn't want all that mess....

My set up is

1. Super DIY friendly

2. Very light weight and makes your floor concrete solid almost without adding extra weight.

3. Small thermal mass makes it possible to shut down when not needed.


Unfortunately I don't have extra time to do some tests and compare performance of different systems.

My set up is not something new it is hybrid between staple up and top floor installation. This set up is possible when your house is finished and you will need minimum intervention in it's existing structure. Stair case is a real pain and unavoidable.

[berniebenz]

Originally Posted by Vlad

1. Yes pex is spaced 12" apart. 6" spacing is impossible in my case because it will make pex loops too long. Plywood is 5/8" and not 3/4".

2. Read this first: Physics of Foil: Radiant Barrier Stops Heat Gain & Loss in Buildings

3. Omega shape is a slot or bend shape in aluminum plates. It locks pex tube.
http://www.pexuniverse.com/store/pro...ates-htp122100
PEX Heat Transfer Plate - Stamped Heat Transfer Plate

4. This is a point to insulate top plywood from subfloor. For this reason I didn't want to fill the gap between loops.

5. I checked concrete / gypsum options. Very expensive in our area. Also I didn't want all that mess....

My set up is

1. Super DIY friendly

2. Very light weight and makes your floor concrete solid almost without adding extra weight.

3. Small thermal mass makes it possible to shut down when not needed.


Unfortunately I don't have extra time to do some tests and compare performance of different systems.

My set up is not something new it is hybrid between staple up and top floor installation. This set up is possible when your house is finished and you will need minimum intervention in it's existing structure. Stair case is a real pain and unavoidable.

Valad,
The point of my critique is not at all to put down your design nor your decision to implement it for your purposes, rather it is intended to give others insight to alternatives from my perspective and experience, which I hope will be constructive, such as they are.

Back to your numbered comments to my critique:

1. A major problem with PEX. ½” ID PEX is too stiff to comfortably conform to 3” radius, 180 degree return bends. Not so with polybutylene, which I have used effectively within this constraint.

2. Some pragmatic physics of IR radiation in heat transfer that you may have overlooked: Polished Al is effective in reflecting IR only under specific circumstances. The radiation must be traveling thru free space, i.e. clean air, at the point of impact with an absolutely clean, dust free reflecting surface. Why such surfaces facing up very shortly become ineffective reflectors because of dust particle accumulation . The reflecting surface must be facing free space, not in contact with another solid or liquid, clean air being an acceptable compromise. Thus, your upward facing Al foil is of questionable long term value, even where it is exposed to space radiation, overhead air, and not in contact with wood strips.

3. Your sheet metal Al heat transfer plates being only 5” wide are obviously designed for 6” tube spacing to be at all effective in a non conductive environment such as yours. At almost $0.70/ linear ft, that is at least $1.50 per sq ft of total floor area with tubing spaced at an optimum 6” on center, inasmuch a they can not be bent into any return or even a slight bend. Their cost effectivity is very much in question!

Again, no put down intended, just another perspective for others to consider.

[Vlad]

berniebenz,

As I said before, unfortunately I don't have extra time to test and compare concrete VS sandwich installation.

I don't claim this set up as my design. I just didn't want to deal with concrete. My house is 3 store so I would need concrete pump to pump and whole crew of concrete workers (most of them used to work like "animals" and would damage pex tubes by walking on them etc...)

Under subfloor is a pain to install especially if you have drywall already in place. The sandwich option I found on YouTube was kind of start point for me. I made some changes and I like them.

We live in 2012 and I don't think somebody uses polybutylene tubes any more. The only material for radiant floor heat nowadays is pex.

To place pex @6" was not needed in my case. Actually I have 10 heating zones and my large rooms exceeded maximum recommended 300' length. 300' length @6" only gives you 12'x12' room plus you need extra to run to manifold. My smallest room (den) is 12x12. In my case some runs to manifold from 3 floor were about 50' each, that left me only 200' of pex for room heating. I did insulate all runs with 1/2" pipe insulation.

Also as I mentioned before my actual supply temperature and flow rate are much lower then most guru recommend. The temperature in supply most of the time in 85-87F range and flow is less then half of what is recommended. If I had a problem with delivering heat my loop temperature would be much higher and flow rate as well.

Even in winter time every time I touched manifold I was thinking "this hardly even warm water can't heat up the house" but it did.

Now some numbers. Last year we used only electric heaters. We only heated parts of the house we needed. Our electric bill was extra 300$. This year with 65% efficient (max) DHWT we pay extra 100$ for gas (100$ VS 300$ ). Also we heat up 24/7 whole house 3000 sft.

I do like comfort but I still need to work on ventilation part of HVAC including central AC. Also I want to go toward GSHP (my drilling project finally started to show some progress ) and keep DHWT only as an emergency back up. If ground loop performs well I will use another GSHP for DHW.

Many people asked me to post more info about my radiant floor project but I wanted to make sure it worked first. Now after this winter I can say it does work and works very well. I don't sell it or make money from it I just want to share this as I think successful project.

If somebody wants to compare it to conventional concrete set up please go ahead I just don't have time for this.

[Vlad]

Originally Posted by berniebenz

Valad,

3. Your sheet metal Al heat transfer plates being only 5” wide are obviously designed for 6” tube spacing to be at all effective in a non conductive environment such as yours. At almost $0.70/ linear ft, that is at least $1.50 per sq ft of total floor area with tubing spaced at an optimum 6” on center, inasmuch a they can not be bent into any return or even a slight bend. Their cost effectivity is very much in question!

Again, no put down intended, just another perspective for others to consider.

I ordered 1000 plates and still have about 200 left. 800 plates was enough for 3000sft. You don't need to bend them. You only use them on straight runs. Why would you bend them?

If I set loop temperature to 110-115F as many recommend and recommended flow I will simply fry everybody in my house. So efficiency is good.

[AC_Hacker]

Vlad,

I have read all of your radiant floor install report.

Thanks for the information, but I have more questions...

What kind of PEX did you use?

• PEX-AL-PEX?
• Oxygen Barrier (coated)?
• Non-Barrier?

Did you use any kind of silicone glue or silicone lube between the PEX & the aluminum spreaders?

Do you have any heat-up or cool-down noise?

You said that your house is three-story high...

• Is it on slab?
• Is there a basement?

...if it has basement, is the basement insulated?

How much insulation do you have in the walls of the house?

Are your windows

• Single-glass?
• Double-glass?
• Triple-glass?

How much is your roof/attic insulated?

• Did you have any especially cold weather during the winter?
• What was the temp at that time?
• Did you measure the water temp coming out of the DWH at that time?
• Did you measure the water temp returning to the DWH at that time?

Thanks,

-AC

[berniebenz]

Originally Posted by Vlad

If I set loop temperature to 110-115F as many recommend and recommended flow I will simply fry everybody in my house. So efficiency is good.

I don’t think that is a qualitative measure of efficiency.

[Vlad]

Originally Posted by berniebenz

I don’t think that is a qualitative measure of efficiency.

Sorry, I meant effectiveness. In my language this two words are interchangeable.