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Radiant Floor Heat

See our 22 Myths companion page
how radiant myths get spread.

This is a list of what gets said on the internet by so called experts and our rebuttal with the facts.

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This article has unwound some wound up personalities so if you only think in black and white, believe straight lines are natural and have no sense of haha then you are far too serious to read this text.

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Radiant Heating Myths

Radiant Mythology
22 Myths About Radiant Under Floor Heating

Have You Heard of A Myth and Want Us To Explore It?

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A NEW (Old) Myth

Myth: Radiant heated systems have lower air temperatures at the ceiling so there is less heat loss.

The Facts: Whilst it true that radiant floor heating systems tend to have more consistent air temperatures from floor to ceiling, and possibly lower ceiling air temperature than some homes heated with furnaces...the fact is  radiant heated floors will raise the temperature of the ceiling mass by radiation. Any surface in the room for that matter, which is cooler than the floor will absorb its heat in the endeavor to equalize the mean radiant temperature throughout the space. 

This heat balance does  create excellent comfort but does not necessarily create less heat loss at the ceiling.

Myth: Radiant tubes shall not be longer than...fill in the blank.

The Facts: There is no magic number for loop length.* The length of a radiant loop is driven by hydraulic evaluations based on fluid velocities.

Flow velocity is a function of the pipe diameter. Head loss (∆p) is a function of velocity.

Total differential pressure (∆p) requirement  is a function of length amongst other losses. Overcoming the resistances is based on the circulator selection with motor efficiency the prime objective. For greater details read:
Heat Loss to Head Loss.
*Some codes like CSA B214 restrict lengths for good practice.

Learn how to avoid six common mistakes

Radiant Installations - The Good, Bad and Ugly

Radiant Mythology
22 Myths About Radiant Under Floor Heating and Cooling
Copyright 2004-2016, Robert Bean, All Rights Reserved

2014 was the 10th Year Anniversary for, "Radiant Mythology: 22 Myths About Radiant Under Floor Heating and Cooling". Since 2004 this single article has caused more tightly wound up individuals to explode/implode than any other thing I've written. It has brought me countless hours of entertainment and wonderful nastygrams and I hope to wring out the last bit of joy right up until each myth is vaporized.

For additional support visit our visitor services page.

Myth #1 - Modern Radiant Heating and Cooling

Myth #2 – Everyone Knows Heat Rises

Myth #3 - Radiant Floor Heating Emits Harmful Rays

Myth #4 - Radiant Floor Heating Causes Varicose Veins

Myth #5 - Radiant Heating Is Slow

Myth #6 - Radiant Heating Systems Are Susceptible to Freezing

Myth #7 – Radiant Heating is 30% More Efficient Than Air

Myth #8 - Efficient Homes Heated with Warm Floors

Myth #9 Radiant Floor Heating Dries Out Hardwood Floors (Facts on Humidity)

Myth #10 - Radiant Floor Cooling Doesn’t Work and It Causes Condensation

Myth #11- Radiant Heating Causes Pink or Yellow Floors

Myth #12 - You Don’t Need Radiant On The Main Floor, The Basement Will Heat The WHOLE House.

Myth #13 - Use a Water Heater Instead of a Boiler.

Myth #14 - If You Use Radiant You Have to Increase Your Slab Thickness

Myth # 15 - The Bigger the Radiant Pipe The More Heat You Will Get.

Myth #16 - If You Use Zone With Circulators Instead of Zone Valves You’ll Never Lose All Your Heat.

Myth #17 - You Need To Have A Furnace For Air Movement For Indoor Air Quality.

Myth #18  - Radiant Heated Pools and Water Beds

Myth #19 - You Don’t Have to Spend Money On Light Weight Concretes or Gypsum Poured Floors – You Can Use Sand. (…or pick another favorite and silly substitute)

Myth #20 - You Don’t Need To Buy Pipes With Oxygen Barriers When You Can Use Chemicals to Control Corrosion

Myth #21 - Floor Coverings Are Damaged By Floor Temperatures Over 85 Deg F

Myth #22 - You don’t Need That Expensive Rigid High Density Slab Insulation When You Can Use The Low Cost Reflective Bubble Foil Insulation.

Read All the Details - Download the Complete Article  

Advisory on Reflective Insulations from Canada, United States and New Zealand.

More myths coming to you via the rumor mill...

Myth #23 - Radiant output...can you really get 40 Btu/hr/sf?
Not if you want to stay comfortable!
Click here.

Myth #24 - The bigger the zone valve the better...oh really?
According to Decision Analyst (tm), over 50% of homeowners are dissatisfied with their HVAC of the reasons - oversized equipment! This is a technical topic which you can learn about here.

Myth #25 - Water heaters vs boilers...
We shake our heads daily over this...
Click here.

Myth #26 - Radiant pipes will leak.
PEX is a product not like copper, or rubber or some plastics like polybutylene. There are uninformed people roaming the earth claiming to be experts who just haven't been paying attention to the past several decades. All over the world the very same PEX pipe used in military applications, bridge decks, helicopter landing pads and other brutally challenging applications is installed in your home.  In fact the PEX used in residential applications is overqualified for the application!
Click here for more info.

Myth #27 - Radiant heating saves energy. 
Lets get back to basics.  The first law of thermodynamics states energy can neither be created nor destroyed...ergo it can not be saved by any type of heating system...not even radiant. All one can control is how effective energy is converted into useable heat without creating a lot of parasitic heat transfer.  Ask yourself this question..."why am I creating temperatures of thousands of degrees by burning fuel when all I need is less than a nominal 120 deg F?" How logical is that? To improve the effectiveness of energy conversion we can use low temperature devices like condensing boilers and heat pumps, which are better matched to low temperature systems.  Conversely we could burn fuel to create steam and use it to generate power and then use the condensate to heat the space.  For more details on this myth read about exergy. That’s right ‘exergy’ – not energy.

Myth #28 - When it comes to radiant; tile and concrete are better than carpet and wood.

The ability for a material to radiate heat is based on a term called “emissivity” and every material including your skin has a rating.  The rating scale is between 0(zero) and 1(one). One is the perfect emitter and zero is the worst. 

There is a relationship between emissivity and reflectivity. In very general terms what makes a lousy radiator makes a good reflector.

Shiny and smooth materials like aluminum foil or polished steel have emissivities as low as 0.04 which is why they are good reflectors. When it comes to floor coverings, tile, concrete, wood, or carpet have very high emissivities between 0.9 and 0.96. What does this mean? It means these floor coverings when operating at the same surface temperature will radiant the same amount of heat. The confusion lays between people’s lack of understanding in emissivity and thermal resistance. Carpet has a higher resistance (makes a better insulator) which means (all things being equal) it will require higher fluid temperatures in the pipe and or more pipe to get it to the same surface temperature as the tile or concrete. Carpets may feel warmer than tile, but not because of the surface temperature - carpet feels warmer because it does not draw heat out of your feet at the same rate as tile.

When it comes to radiant heating 99.99% of all floor coverings work equally well as radiators.

Learn more about emissivity here.

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