DIY Hydronic Floor Heating

[AC_Hacker]

Restored Roman Hypocaust (more pix...)

Hello all...

I have noticed that there is interest here at Ecorenovator in hydronic floor heating (AKA: radiant floor heating). Also, because of the friendly relation between Ecomodder and BuildItSolar, I should mention the great interest in hydronic heating on that site.

In my thread, Homemade Heat Pump Manifesto, there have been several posts that contain questions or information about hydronic floor heating, and I thought it would be a good idea to create a new thread as a repository for that information and for future conversation and information.

A few basics:

• Hydronic heating uses heated water flowing into some radiating device to provide heat to an enclosed space.
  
• Hydronic floor heating uses an entire floor as a radiating device to supply heat to an enclosed space.
  
• Since the area of the floor can be considerably larger than the area of a typical radiator, the possibility exists that the temperature of the working fluid in the floor can be lower than the temperature of the working fluid in a typical radiator, to satisfy a given heating need. It is because of the lowered required temperature that the potential for greater efficiency can be found.
  
• Typical hydronic floor heating schemes include (in order of efficiency):
  1. On-slab concrete floors with embedded water-circulating pipe. These floors are typically 3 inches (< 7 cm) thick and are insulated, at least at the perimeter, with plastic foam insulation, from the earth.
  2. Above floor installation, wherein a thin concrete (about 1.5 inch) or another thermal conducting layer carries water-circulating pipe.
  3. Under floor installation (AKA: staple-up) wherein water circulating pipe is affixed underneath the existing floor, often with aluminum spreader-plates to enhance thermal transfer. For this scheme to be effective, insulation underneath the water circulating pipes must be very good.

As I understand it, in Europe where energy costs are very high, hydronic floor heating accounts for around 80% of new construction, with the remaining 20% accounting for all other forms. In the US, where our energy policy is essentially subsidized by our military spending, hydronic floor heating accounts for less than 10% of new construction, with the remaining 90% accounting for all other forms.

The best reference book I have found so far on the subject is Modern Hydronic Heating by John Siegenthaler. It is expensive but very thorough.

However, it does not address DIY approaches and is pretty light on 'Heat Pump + Hydronic Floor Heating' which offers very high efficiency. Topics like 'Solar Assisted Heat Pumps + Radiant Floor' go un addressed.

(* NOTE: the URL for Modern Hydronic Heating does list other books, apparently by other authors that do address other interesting approaches (solar thermal, etc.) to heating. Also on this site is a download section where 15-day trial software, pertaining to hydronic design, is available. Much can be learned from trial software. *)

For approaches like DIY retrofits, where benefit per dollar can be greatly enhanced by scrounging, re-purposing and completely novel thinking, enormous potential can be found.

Yes, this time, David can really kick the Giant's butt.

Some useful links:

• Residential Design and Installation
  
• Keeping the Heat In - An incredibly thorough treatment of insulation.
  
• HEAT GAIN AND LOSS SHORT FORM
  
• Useful Hydronic info
  
• Directory of energy related software, some free
  
• Here' a boatload of on-line videos specifically about radiant floor heating. Some are about electric radiant, others about hydronic radiant.

Best Regards,

-AC_Hacker

Diagram of Korean Ondol (more pix...)

[Daox]

Excellent idea AC Hacker. I'm working on getting my own copy of that book for reading. It seems to be the only worth while one out there. Sadly, since hydronic heating is used in such a small amount of US homes, I doubt we'll find a ton of good material on it elsewhere. If anyone has any good links, please share them.

[AC_Hacker]

I found a link to a page with a very thoughtful discussion regarding radiant floor heating. I found it particularly interesting when radiant floors are considered in the context of High Performance Buildings, and how radiant floors may never develope that 'warm feeling' in a High Performance House because so much of the radiating heat is retained by the house, that lower floor heat levels are called for.

I have been to some lectures regarding 'High Performance Buildings', and they don't use that term lightly. High Performance Buildings are very similar to the Passive House definition. To achieve those levels of performance, buildings needs to be High Performance by design. Stringent efforts to retrofit existing structures can result in achieving 35% to 50% of the Passive House standards.

So I think that 'warm feeling' would still be there.

Also, the discussion apparently assumes that no one would DIY a radiant floor. So their cost estimates are stratospheric by DIY standards.

Regards,

-AC_Hacker

[AC_Hacker]

I talked with a local hydronic guy who told me that around here, feed water temperatures are:

• 80 to 85 degrees for tube in slab
• 100 to 110 for on top of floor heating
• 120 to 130 for below floor (AKA: staple up) heating

* * *

And just to get the thought process moving, here are some radiant floor links...

• Here's a house heated with water from a solar shed, featuring DIY radiant floor heat. It utilized the large radiant area of the floor to compensate for the lower feed temperatures of the solar system. As a bonus, the solar collectors work more efficiently, too.
  
• Guy Marsden does a 3" solar heated slab in Maine (w/propane backup).
• (...the 'NEXT' tab at the bottom will take you to the other two pages...)
  
• Here's a solar shed with a hot water heat storage feature. No radiant floor, yet.
  
• Here's a link to a company that supports DIY. The web site is filled with grest photos & descriptions. They also have a free downloadable design manual available here. The manual pretty much duplicates the web site, photos not as good as the web version. There's good info here, but a fossil fueled boiler is assumed, so their 'rules-of-thumb' may not hold with the lower solar or hydronic feed temperatures.
  
• Here's a page from Radiantec, also supportive of DIY, with free manuals too numerous to list. Raniantec also has a list of Solar heating articles, why not combine the two?
  
• HouseNeeds hosts a Hydronic Heating University.
  
• InFloor has a free Deluxo Design & Installation Guide.

[Daox]

Originally Posted by AC_Hacker

I talked with a local hydronic guy who told me that around here, feed water temperatures are:

• 80 to 85 degrees for tube in slab
• 100 to 110 for on top of floor heating
• 120 to 130 for below floor (AKA: staple up) heating

Wow, that would indicate that in slab would be MUCH more efficient. Especially in a heat pump situation I'd imagine. I knew under floor had to be pretty hot, but its nice to see on top of floor in the mix too. Good info AC Hacker!

I'll hopefully contribute to this thread soon, been so stinkin busy lately.

[AC_Hacker]

Originally Posted by Daox

Wow, that would indicate that in slab would be MUCH more efficient. Especially in a heat pump situation I'd imagine.

As I mentioned, the hydronics guy is referring to conditions around here, and the weather is much milder here than in many parts of the country and world (must remember we have an international audience here!). The feed temps would be higher in areas where the heating demands are greater, but the ratios would stay pretty close.

Nicolas Léonard Sadi Carnot

Heat pumps, in their present state of development, have difficulty making feed water temperatures much over 120. And the Carnot theorem indicates that efficiency is increased as Delta T is decreased. So heat pump + staple up hydronic heating is not a good match.

Here's a table of Thermal Conductivity of common materials...

The reason a slab is more efficient is that concrete is a pretty good conductor (k=0.42 to 1.7), at least compared to wood or MDF (k=0.12 to 0.17), etc. Another reason favoring concrete and gypcrete (AKA: 'the wet system') is that the slab is poured over and around the PEX, so conduction from the PEX to the concrete is assured. The aluminum (k=250) plate idea , even with a U-bend in them are not in 100% contact with the PEX... conduction needs contact.

But weight is a big factor with the slab on a suspended floor, and I have been working and testing and researching this problem for nearly a year. I think I may have come up with a way to keep cost and weight down and performance at an acceptable level.

Stay tuned...

-AC_Hacker

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[TronHopper]

Originally Posted by AC_Hacker

I talked with a local hydronic guy who told me that around here, feed water temperatures are:

• 80 to 85 degrees for tube in slab
• 100 to 110 for on top of floor heating
• 120 to 130 for below floor (AKA: staple up) heating

* * *

And just to get the thought process moving, here are some radiant floor links...

• Here's a house heated with water from a solar shed, featuring DIY radiant floor heat. It utilized the large radiant area of the floor to compensate for the lower feed temperatures of the solar system. As a bonus, the solar collectors work more efficiently, too.
  
• Guy Marsden does a 3" solar heated slab in Maine (w/propane backup).
• (...the 'NEXT' tab at the bottom will take you to the other two pages...)
  
• Here's a solar shed with a hot water heat storage feature. No radiant floor, yet.
  
• Here's a link to a company that supports DIY. The web site is filled with grest photos & descriptions. They also have a free downloadable design manual available here. The manual pretty much duplicates the web site, photos not as good as the web version. There's good info here, but a fossil fueled boiler is assumed, so their 'rules-of-thumb' may not hold with the lower solar or hydronic feed temperatures.
  
• Here's a page from Radiantec, also supportive of DIY, with free manuals too numerous to list. Raniantec also has a list of Solar heating articles, why not combine the two?
  
• HouseNeeds hosts a Hydronic Heating University.
  
• InFloor has a free Deluxo Design & Installation Guide.

Hey AC_Hacker,
Its really great idea. I will also work on it.

[Christ]

Good information! I plan on using radiant floor heating with a solar/water setup that thermosiphons, and using valves and a bypass loop for excess heat energy, with ~1000 gallons of stored fluid in thermos-like insulated tanks under ground, for the times that there isn't sufficient sunlight for days on end.

For fluid, I plan on either using salt/water, if I can get enough plastic tubing, or using a methyl/water solution. The fluid should never freeze, since the lines and tanks will be buried under the ground, so that they should maintain an atmosphere of at least 50*.

I may have to go against the thermal siphon idea, though, because it may not work fast enough to actually keep the home warm.

The floor is most probably going to be insulated poured concrete (which may end up being mixed with styrofoam beads) with an overlay. Some rooms may have partial brick/stone floors as well, which add thermal mass and thermal dispersion potential. (Acting like a heat retainer that also helps disperse heat across a larger surface area.)

[AC_Hacker]

Originally Posted by Christ

The floor is most probably going to be insulated poured concrete (which may end up being mixed with styrofoam beads) with an overlay. Some rooms may have partial brick/stone floors as well, which add thermal mass and thermal dispersion potential. (Acting like a heat retainer that also helps disperse heat across a larger surface area.)

The styrofoam beads will reduce the thermal conductivity of the concrete...

Last summer, I was testing the thermal conductivity of various aggregates in concrete, and one of my test aggregates was aluminum chips. Made sense, beings as how aluminum is light and a wonderful conductor of heat. What I didn't count on was that the alkaline nature of concrete made the aluminum fizz, and the concrete+aluminum puffed up with a ka-jillion little bubbles and was a worse thermal conductor than plain old concrete.

The rest of your ideas sound really great.

[Christ]

Originally Posted by AC_Hacker

The styrofoam beads will reduce the thermal conductivity of the concrete...

Last summer, I was testing the thermal conductivity of various aggregates in concrete, and one of my test aggregates was aluminum chips. Made sense, beings as how aluminum is light and a wonderful conductor of heat. What I didn't count on was that the alkaline nature of concrete made the aluminum fizz, and the concrete+aluminum puffed up with a ka-jillion little bubbles and was a worse thermal conductor than plain old concrete.

The rest of your ideas sound really great.

What I meant by overlay is that the water pipes sit on top of the concrete. The foam beads mixed in the concrete are a recycling method for stryrofoam, which doesn't biodegrade, and help act as insulation against thermal transfer, as I understand it.

So the actual floor layout is concrete/hybrid slab, fluid lines laid on top, flooring options laid over that.

I figure 170* is more than enough to heat the floors and the rest of the house, right? (The temp that solar thermal setups can reach, even on not-so-great days.)