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Radiant Heat is Affordable! – Who Knew?

by Chad Ludeman on December 17, 2007 · 6 comments

in budget,Building Science,Development,HVAC

I mentioned in our last design meeting, we had decided that radiant heating was definitely a necessity and no longer a want. Well, I did a bit of research last week on various radiant heating systems and just received my first call back from a company called Radiantec who confirmed that radiant systems can in fact be affordable!

Don Vance from Radiantec is handling our quote and roughly estimated that the materials needed for our radiant system would most likely come in under $2,000. This is much less than our original estimates of $10K or $15 psf for a complete radiant heating system for the home. As I was doing research on radiant I found that this is a common misunderstanding and most people not familiar with radiant assume it is a premium system that is only available at equally premium pricing.

It is true that not all radiant systems can be affordable, especially those that use fancy products that combine your subfloor with the PEX tubing to heat the floor in one sheet. Here is a brief rundown on what should make our radiant system a very affordable and comfortable heating option:

  1. The house is small and well insulated. The average home is large and very poorly insulated, requiring multiple zones and large heating sources or multiple heating sources.
  2. The house will have only one zone on the ground floor. With our open, loft floorplan we can easily heat the second floor without installing radiant heat on the second floor at all. The heat will simply rise to heat those areas.
  3. Concrete slab installation. There is added expense and complexity for installing radiant under a wood framed floor. With concrete slabs it’s as simple as zip tying the PEX to the steel reinforcement prior to pouring the floor. The use of the slab will also add mass and retain the heat for a much longer period of time than a thin, wooden floor.
  4. Potential sweat equity savings. Anybody can zip tie PEX in place prior to pouring the concrete. No need to pay an expensive plumber or HVAC installer for this step.
  5. Zero floor coverings. By eliminating the need for floor coverings in our design we have allowed the heat to be transferred directly to our feet with no insulation loss to a floor covering. The heat will also rise through the second floor much easier with an open truss design and no floor covering on the second floor.
  6. Utilizing an existing “free” heat source. Since the home is so small and well insulated we should easily be able to use one water heater to heat the floor and the hot water for the home. Since we need to buy a water heater no matter what, this makes the heat source “free” for the radiant system.

The most efficient method for radiant in the home will most likely be an “Open Direct System” as seen in the diagram below from Radiantec’s site.
Open Direct System for Radiant Heat

An open system allows you to mix the radiant system’s water freely with the home’s hot water and use one water heater while adding the fewest amount of plumbing accessories to the system. It is also the perfect type of system for adding a solar hot water array to the system which is still an option for our homes. Radiantec has a solar division that operates as a non-profit in order to provide the best cost solar systems as possible to the public. Here is a diagram of what our system could look like with solar added to the equation.
Solar supplement to radiant heating system

Don will be quoting this option for us as well which I am excited to see. Either way we are currently planning to provide the hookups for a solar supplement in the future if we can not afford one up front in the $100K figure. We like solar hot water systems as they can be much more cost effective and efficient than solar PV systems. If the homeowner wants to add a PV system in the future to become zero energy or carbon neutral, their required system size will be much smaller with a solar hot water system already installed.

Radiantec was not the only company I contacted so here is a brief list of some other good resources I found:

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{ 6 comments… read them below or add one }

1 brandon December 18, 2007 at 2:33 am

That’s great to hear. Lots of great info on this post as well as the links you provided. Gives me hope for my next house. Now if only I can find a reasonably priced shell in a nice neighborhood. Haha.

2 Derek January 31, 2008 at 2:06 pm

Hi from downunder,

I did some research on this.

The economics is based on several factors:

* Energy source
* Climate
* Occupancy

The cheapest is solar followed by natural gas.

Hydronics are best suited for buildings in cold temperate/alpine conditions with high occupancy rates when the system needs to be used all day.

Constantly switching off or re-zoning wastes heat and requires recharging the slab each time you use the area.

The problem with solar hot panel is that there is not much sunshine when heating is most important. You need a lot of them to adequately heat the slab.

I have also read that a good direct passive solar gain design eliminates the need for hydronic. Better to heat the slab directly by the sun then suffer efficiency losses from the solar panel or hydronic system.

3 Derek January 31, 2008 at 2:06 pm
4 loretta reidy October 23, 2008 at 10:10 am

How do you stop heat loss is a house that has a loft. Even though I have 2 zone heating all the heat from downstairs rises to the 2nd floor loft area leaving downstairs cold and a high energy bill. Any suggestions, this is a new house and the nergy bills are high.

5 chad October 23, 2008 at 2:02 pm

Insulate the envelope better. A well insulated house that is very tight will not have significant variations in temperature like a normal house.

6 Derek October 23, 2008 at 7:48 pm

In radiant floors lot of heat actually conducts out of the slab into the surrounding ground. Insulating the slab is also critical for these to function efficiently.

Convected hot air will naturally stratify regardless of your insulation. Either prevent it rising to the loft by closable openings or use a forced convection system (fan) to recirculate it back down again.

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