Radiant Heat Systems



The basics

The process begins when either a boiler or a geothermal system heats water that is then pumped through tubing underneath the floor’s surface. The heat generated from the hot water will then rise and warm the floor above.

There are many different ways to install hydronic radiant floor systems. While each method may go by a different name depending on a contractor’s training, the process is the same.  Here are four common types.

A “slab-on-grade” system usually refers to a concrete thickness of 4″ or greater.  The tubing is tied to wire mesh above rigid insulation, then poured concrete is added above.  This system might commonly be found inside large buildings, garages, or basements.  This system stores heat for a long time due to its large mass.  But this also makes it able to respond quickly to re-heat the room when a window or door is opened.  Snowmelt systems would be also be classified as slab-on-grade if they are heated by liquid.

A Dry Below (dry meaning without concrete slurry) or “staple-up”, has tubing installed underneath the subfloor from the room below. Metal plates are then installed as the tubing goes in to help spread out the heat on the floor above. Before a subcontractor finishes the drywall from the lower room, usually foil-faced insulation must be placed below the tubing to reflect the heat upward and prevent heat from escaping to the lower level.  This is slightly less efficient than some of the other methods as the water temperatures have to be higher to achieve the same results.

In a “Dry Above” system, the tubing is installed directly onto the sub-floor. The tubing is fit into place into recessed plywood forms and/or furring strips with aluminum plates, and the finished floor is installed above this.  Floor covering could be tile, stone, or carpet.

Most experts agree the most efficient method is an in-floor radiant system or “Thin-slab”. The tubing is installed directly onto the subfloor with gypsum poured over it, making the tubing part of the floor. The flooring material is then placed on top.  This system can use the lowest water temperatures and is a good fit for a high efficiency boiler or even solar systems.  It can store enough heat to work well, but also cool down more quickly to avoid overshooting desired target temperatures.  This method can also produce very even surface temperatures and has the added benefit of making the floor very quiet.

Conveniently, radiant floor heating works with most any type of flooring material, but solid surfaces produce a better heat transfer. Regardless of the flooring material you choose, it is imperative to have the right amount of insulation underneath the tubing so the heat will go where you want it to go.

The design

In order to implement a radiant floor heating system, contractors must first consider the home’s design and solar gain potential because they can affect the process. These factors can then determine the complexity of the design.

We look at the structure of the home, windows, doors, the insulation values, and how it’s built to prevent heat load or loss. The heat loss will be calculated by one of our specialists, so we can design systems around those calculations, and they tell us how much energy we will need to heat the home on the coldest day of the year.

The next step is to talk about what our customers want out of their heating system, how they will be using each room and how warm they want their home when it’s freezing outside – so we can design the system accordingly.

Although we try to keep our systems as simple as possible to hold down the energy costs and maintenance requirements, we can zone as many areas to different temperatures as you desire.  More zoning increases overall system cost and complexity, and usually the old rule, “simpler is better” applies to many of our systems.  Our newest systems focus on using the least amount of energy to do the job.  We are always doing research to find the best products that are proven to work well.

Radiant floors are not really “hot”.  They should feel neutral or maybe just warm depending on the outside temperatures. It is recommended to separate common areas or rooms of the home into “zones” depending on solar gain potential and the usage.  Most of our boiler systems use “smart boilers” that only heat the water to the necessary temperature to heat the house on any given day.  We also use “smart” pumps that use less energy.

The benefits

The best reason for deciding on a radiant floor heating system is to understand the benefits. While the initial expense of an effective system may cost more than a traditional forced air heating system or even hot water heat,  you will be reaping the rewards for years to come. It likely could cost less than your new car but last many more years.

Even though radiant heat systems can be located in the walls or ceilings as well, the most common radiant heat systems are in, on, or under the floor.  They all heat the objects and the people in the room, rather than just the air or the room itself. With radiant floor heating, everything in the room is that specific temperature. You’re comfortable. You can sit by the window or door and not feel a draft.

Radiant floor systems are quiet since there is no blower. And without a blower, the air quality in the home is significantly increased since there are no dust, dirt or allergens circulating throughout the air.

Radiant floor systems heat the space for a much lower cost. By using an infloor radiant system as opposed to a forced air system, you can save as much as 30 percent in utility costs. This was proven by building identical houses side x side and installing radiant heat in one, and a forced air system in the other and comparing energy costs over time.  The boiler and the furnace had the same AFUE efficiency ratings to start with, but the delivery method is totally different.  Forced air systems cause more heat loss and less even heating in the room.

Toasty-warm floors feel great underfoot. But how does a hydronic radiant in-floor heating system stack up to other heating methods?

What are the major advantages of hydronic radiant in-floor heating?

  • It puts the heat where you are. You’ll feel the heat through the floor everywhere in the room.
  • You can avoid installing duct-work or registers, which both take up space and restrict how you arrange your furniture. “It’s invisible—your floors become your radiators”. Water is a much more efficient way to deliver heat inside a building than a heated air system.
  • It’s cleaner than a forced-air system because you aren’t blowing dust or other allergens around.
  • It’s efficient. While it’s difficult to compare precisely, hydronic radiant in-floor heating doesn’t NEED to heat the whole room space ABOVE YOUR HEAD focusing on your body trunk only. Rooms or zones can be controlled independently. You can save money by keeping certain rooms cool. In addition, radiant heat does not dry out the air inside thereby keeping good humidity levels higher which contributes to better life for household furniture and computers with less static electricity.
  • Because in-floor heating is considered a premium heating method, it may add to the resale value of your home.

Are there any disadvantages or tradeoffs? 
It’s just a heating system, not a full HVAC system. You may want to install other equipment, such as air conditioning. With some systems we install high velocity stand-alone air conditioning systems to take care of the cooling loads. These systems mix the air better and give better overall comfort levels.

Is it possible to combine radiant cooling and heating within the same system?
Yes, there is a method to accomplish both heating and cooling with the same system, even though the tubing itself may be in the floor and on the ceiling.  The control becomes more important with these systems and the water temperatures in the cooling mode have to be closely regulated.

How does a hydronic in-floor heating system work? What are the key components?
A heat source warms up water. (Usually, that’s a boiler; but, in some small installations, a hot-water heater certified for space heating can be used.) That warm water is then circulated through pipes in the floors via a circulation pump. A radiant thermostat allows you to control the water temperature by zone or room.

What’s in those pipes?
Most residential hydronic systems use water, but a glycol solution, which freezes at a much lower temperature than water, may be used in seasonal homes or cottages. (The freezing point of the glycol solution depends on the concentration of glycol used.)  We typically add other agents to the water to stabilize the system and prevent corrosion to components.

Could the system leak?
Of a typical hydronic installation with PEX (which is “cross-linked polyethlene” pipe), any leaks we ever had were man-caused, (such as someone drilling through a pipe already in place).   Properly designed, installed, maintained— most piping is guaranteed for 25 years if installed to the manufacturers specifications.  If your home will go unheated for more than a week in subzero conditions, you may want or have to add a glycol solution to your system fluid.  Draining or blowing out a system can have other negative effects as air can cause rust damage to an open system without fluid.

We have whole house pex plumbing and radiant heat systems that are already over 23 years old with no leaks. Most bad reviews on radiant heat systems are caused by “untrained homeowner type installations” or kits from online resellers that have improper designs.  That said, we do work with “do-it-yourself installers” and provide training to make sure it works properly.  Most of the time, we will install the boilers and other components that require more professional knowledge to work properly and to guarantee good warranty coverage from the manufacturers.

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