Robert Koci
Install once and you will hate all others
Canadian Contractor Building Materials Business Damage Environment Fire HVAC LossThe best method of heat supply on the planet
By Tibor Kovacs
Our human comfort relies just as much on radiant heat transfer as it does on air temperature, yet the majority of heating and air-conditioning professionals think only in terms of air temperature. As a result, we are missing out on a truly comfortable living environment in our own homes or places of business. By controlling both the air temperature and the radiant transfer, radiant panel systems (hydronics) deliver a comfort that is unsurpassed.
The concept of circulating hot water for heat, as opposed to forced air systems, is becoming increasingly popular. In a forced air system we gather a lot of air, blow it through a fire box and use large diameter metal channels to distribute the hot air everywhere in the building. Air, however, is a very light substance with no thermal mass to it. What this means is that it carries a small amount of heat energy and loses it very quickly. In order to carry substantial heat around this way we need to move a lot of air, which requires a fan that may generate noise, through a distribution system (ductwork). The air may cool substantially before it gets to where it was intended to go. Then we recirculate it and heat it up again. The result is lots of hot air when the system is on followed by a cool down when it is not. The obvious result is temperature fluctuations.
In radiant hydronic systems water is run through a boiler and small diameter piping distributes heat throughout the building. Water has the best capability to absorb and move heat. It soaks up the heat, holds on to it and releases it slowly to the floor. The surface warms up and radiates in the room as soon as there is the smallest temperature difference. To sum up, hydronic systems use less transfer material, provide even heat distribution (due to the thermal mass) and reduce system noise.
Floor heating creates a temperature profile where the warmest part is the floor and the coolest is the ceiling. The vertical temperature distribution is practically even, with the exception of the few inches above the floor surface, which may be warmer. Remember, radiant heating does not heat the air. Heat transfer only happens when the radiant heat waves encounter dense material. This heating method heats up objects such as walls, furniture and the area’s occupants.
It is a direct heat transfer to the body, similar to the sun shining on you in winter, so we are not reliant on the surrounding air temperature. Because the walls are warm there is less heat drawn out from the body. Our feeling of warmth is mostly due to the constant low-density heat radiation with minimal changes. The temperature fluctuation in a radiantly heated room is about 0.5 degrees. Occupants get used to the constant conditions very quickly.
Heat emitters
After the water is heated by the boiler, or geothermal heat pump, it is circulated through the piping to heat emitters. Today the most popular methods of radiant heat emitters are baseboards, radiators and radiant floors, walls and even ceilings. There are a number of differences in the technologies.
Radiant baseboard is commonly a length of metal tubing with fins on it. Hot water runs through it, the metal heats up and transfers the energy to the air around it. The air heats up and starts travelling up, cooler air flows in then heats up, and so on. The main effect is the high temperature tube heats up the air and creates warm convective air currents, which eventually fill the room. There is not a lot of direct radiation coming off it.
Radiators, as the name implies, are the real thing. The hot water flowing through the radiator heats up the body of the radiator and that in turn radiates heat into the room. The surface area of a radiator is much larger than the baseboard and this creates the difference. The air around the unit heats up and starts rising and creates convective currents distributing the heat. There are two main heat transfers here, direct radiation of the surface and convection heating using the air. The main improvement is more even, stable heat distribution. The size and thermal mass of the radiator stores the heat and releases it slowly, evening out the distribution.
In-Floor delivers an even, continuous heat supply. As radiation is a direct function of the surface area it makes sense that the bigger the warmed surface the more heat we get out of it. Compared to the other two delivery methods the surface area available is large. In order to get the same interior warmth, much lower surface temperatures are required to the extent that the floor surface temperature varies between 21C to 29C, most commonly 22C to 23C. This is not a hot floor but is all we need to heat the space to our comfortable temperature. Sometimes it is barely warm, but a properly designed and operating system is never cold. A heated floor normally feels neutral. Its surface temperature is usually less than our body temperature, although the overall sensation is one of comfort. The exception is when maximum heat output is required and the floor may actually feel warm.
Low heat density and warm surfaces, two unique features of radiant floor heating, are two important factors in creating human comfort. The third is even, constant temperature. Lots of research has been done trying to identify the conditions in which the human body feels the most comfortable. We like to be surrounded by warm surfaces that do not draw heat away from us and we love even and constant temperature.
Top Five Customer Questions
1. Can you heat the entire house with radiant floor?
Yes you can and you should. This is the best way of creating maximum comfort.
2. What if the pipe breaks?
The pipe does not break on its own. It only happens if somebody damages the pipe. When that happens a qualified installer should repair the damage.
3. Why is it more efficient?
There are a number of factors adding up to the increased efficiency. Radiant heat does not overheat the air, so the heat loss through the building envelope is less. Radiant heat provides direct heat input into the human body, so the air temperature is less important.
Usually lower thermostat settings result in the same level of comfort.
4. What fuel source can be used?
Any fuel that is available may be used, including natural gas, propane, oil, wood, and electricity. The systems are also well suited to geothermal applications.
5. What happens to cooling?
Ductless or mini split air conditioning systems are becoming increasingly popular. In some situations, they offer the opportunity to “zone cool” resulting in an efficient use of energy.
To see more advanced technical articles related to hydronic heating, please go to www.hpacmag.com and choose “hydronics” in the “search by topic” field.
Tibor Kovacs is the owner of Hydronic Panel Systems/Hydronic Comfort Systems Inc. He can be reached at info@hydronicpanels.com.
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There’s an alternative to hydronic radiant heat – electric radiant heat. These can be either installed in the floor or the ceilings. Their chief advantage over hydronic systems is that they usually cost half of a hydronic system, there’s no need for a boiler to take up valuable floor space, and they are a lot easier to install – especially in renovation type applications. They can also be added on a room-by-room basis as time and budgets permit.
But there are severe limitations to the installation of electric radiant heat, aren’t there? There are governors on the degree of heat you can supply and they can’t be installed in most residential installations because of fire regs, no? And the cost of electric heat is brutal everywhere in Canada except Quebec.
What limitations would those be? Electric radiant heat is installed in all kinds of projects – be it residential, commercial, industrial, etc.
They can certainly be installed in just about any residential application. The only restrictions might be in some very rare cases where the covering material wouldn’t be the most appropriate choice – but hydronic radiant heat is subject to the very same kind of restrictions.
The cost of running electric radiant heat is very cheap, frankly. My own home (approx. 4,000 sq. ft on one floor) was just over $541 last year. Annual average over 5 years was $830. You can read more here: http://www.thermaray.com/greenbuild/sustainable_energy_savings.html
If you’d like a direct comparison between an electric vs hydronic hot water system in identical buildings in the same location, you can find a comparison here: http://www.thermaray.com/greenbuild/electric-radiant-heat-vs-hydronic-radiant-heat.html
While it’s a common perception that electric heat is costly (and this can certainly be true when one is talking about electric hot air systems), the facts are entirely different when you’re dealing with radiant heat.
If you check out the hydro rates in Manitoba you will also find very good rates here.
And as the moderator of this website I must mention for my readers that Steve has an interest in the electric radiant heat as he has some connection to ThermalRay (http://www.thermaray.com), a supplier of electrical radiant heat. Steve, if you could address some of the issues I raised in response to your comment, I am sure my readers would appreciate it.
Sorry about that particular point. It was not my intention to hide any kind of affiliation. Most blogs publish the author’s website URL if provided. I provided such – it’s just that your software doesn’t make that information public. 🙂
I am sure you didn’t do that intentionally.
So, what can you tell me about the issues I raised?
I mention it because I recommended a electric radiant floor to someone for a small room. On my recommendation she installed it, but found that the floor couldn’t keep up with the cold in winter because the floor pad would only heat to a certain temperature because there was a governor on the system that would not allow it to bet any hotter. The room ended up being way too cold.
A number of times I have considered installing electric heat on my own bathroom floor and was told again and again, that i could not do it legally because electric heat was considered a fire hazzard in anything but a concrete bedding under tile.
So, let me be more specific; is there a max temp that the coils can heat to in radiant electric regardless of how much heat is needed to get the room up to livable temps?
And regarding legal installation; can you install radiant electric heat under carpet? under tile? under wood floors?
Sorry that I couldn’t get back to you sooner.
This medium (short of writing a novel) isn’t the best for this kind of discussion, but I’ll see what I can do. 🙂
First, there are a lot of misconceptions imbedded within your statements. All heating systems have an upper limit as to what temperature they can or are willing to supply. For the most part, that’s a safety issue. You can’t reach temperatures that are beyond the safe value for the application. That’s true of electric radiant heat, hot water radiant heat and even hot air heating.
The proper approach to any heating (or cooling) project is to first perform a heat (or cooling) load calculation. This will tell you the total capacity that is required to do the job. Then you select the means that will get you there.
You seem to focus on floor heat. Radiant ceiling heat is often the more cost-effective and efficient choice.
In the case of your recommendation for a small room, what was the room’s total heat loss? What was the capacity of the floor heat installed? If the floor heat couldn’t match the heat loss, then you can expect that the room would be cold on colder days. But that’s true no matter what heating system you choose. Capacity must meet or exceed the heat loss.
As for electric floor heat being illegal except when embedded in concrete, that’s a misconception too. You have to consult the manufacturer as to what is acceptable for their particular product and perhaps the local codes (no manufacturer can keep up with every local code, as much as they try to.)
Often one can install electric radiant heat under carpet, tile and wood floors but you’ll certainly want to consult with the manufacturer of those materials too. (Typically tile is not an issue.) Most manufacturers of hard wood floors say it’s fine provided an upper limit isn’t reached. That upper limit does vary depending upon the manufacturer and the species of wood.
But consider this: when dealing with these floor coverings, is floor-based heat your best option? In many cases it may not be. Ceiling radiant heat tends to be cheaper and offer better performance than its floor counterpart.
Choose the right tool for the job. 🙂
Steve:
Thanks for your thorough reply. I think you responded to the issues I raised well. What is the manufactured max. temp of your products?
In BC electric is much more expensive than gas, with the way BC Hydro now charges extra for homes with above average consumption, the expected 25%+ increase in rates over the next few years, and the current low price of gas.
Unless natural gas prices increase or the carbon tax continues to go up, I don’t see electric heat becoming too popular.
I guess electric radiant heat might be good for homes with severe hot/cold spots who dislike the idea of baseboards- so long as they’re willing to put in a new floor as well.
Steve as to your comments that electric floor heat is cheaper to install then hydronic floor heating you are true with that point. but should you also say that it is more expensive to run than hydronic (warm water) floor heating.
I have had some people say to me that you should do electric snow melt? That sounds rich to run!
What is the payback on one of your electric systems on energy savings?
Is your home floor heated and if so, is it electric or water?
Yes, I have a contracting company and we specialize in Floor Heating and Plumbing. We have been installing floor heat since 1992 and we find that we are still educating people who have never heard of floor heat even at home shows we do every year…
We do recommend electric only when the area is so small (bathroom) that the pumps, controls make the cost out of reach.
I believe in what it can do for my comfort level in my home The one comment is once you have floor heat, you will not have any other heat! TRUE
The 4000 sq. ft home I heat costs me less then $100.00 / month in fuel (natural gas). This includes 110,000 BTU/hr condensing / modulating boiler, all our hot water (80 usg), cooking, dry clothes, and BBQ.
I notice the delivery charges are higher then my gas bill.
You mentioned that if you want you can add a room at a time, as we recommend that as well to our customers. As long as the main controls and piping are setup to have the add-on done, then you are good to go!
The other beauty of hydronic (water) heating is the energy saving in all factors, being fuel, and electrical, as most of the modern system we install run on low voltage 24V and most of our pumps draw less then 1 amp.
Electric floor heat has it place, but I don;t think you would do your whole house or snow melt with it, Would You?
No room in your home for the equipment, then use a recommended absorption heat pump, and maybe cool your home with chilled water, instead of a condenser AC unit.
Water is the most energy saving way of doing heating and / or cooling. Remember the lower the water temperature, the higher the efficiency.
Do it Right, Once!
“Kiss Your Cold Feet Goodbye”
I would like to convert my high efficient forced air oil furnace to electric forced air….
I am considering floor heating in my 200 year old home. Is it possible to heat the existing floors on my main floor? All of the floors are accessable from the basement.