Heating with a Hydronic Radiant System

Hydronic heating is a system which uses water or steam  as a heat transfer medium.  Radiant heating is a method of heating objects by heat radiated from a warmed surface.

Unlike forced air heating, or gravity furnaces, there is little, or no reliance on convection.  In other words, heat is not distributed by moving heated air.  The heat may be radiated from floors, walls, or overhead ceiling panel

The heating system I am going to discuss uses the floor as a radiator.  This is the system I have used in several houses, either partially or as the total heating system.  It is the sole source of heat in the home I have just built.  The same source of hot hater is utilized for domestic use.  I have just installed a more complicated, three zone system, in my sister and nieces new house.  I had also installed a similar system in my sister’s previous home which has operated very well and trouble-free for the last six years.  This system utilizes piping, run under the floor surfaces, to distribute the heat.

This climate reqires a robust heating system

Our heating system has to deal with this climate. This photo was taken in mid November.

While my research and experience is not sufficient to qualify me as an expert, I have certainly gained enough insight for competent comment.  I am going to use a question and answer format, Some of these questions have been  asked of me, and many are questions that I have researched  for myself.

Q/  What about cost?  Isn’t hydronic heating more costly to install?

Not necessarily.  utilizing a single heat source for both domestic hot water and heating reduces cost considerably.  A high-efficiency tankless water heater, and pex pipe, can reduce the cost to less than a conventional forced air system and separate water heater.

Q/  Is Hydronic radiant heat more efficient and have lower operating costs?

I can’t be certain of that without a controlled experiment, but logic would indicate that it is, and my experience seems to reinforce it.  Comfort seems to be achieved with a lower air temperature. As there is little air movement it seems that less heat is lost when a door is opened.  It is ,however a little more difficult to lower the temperature for short periods, such as during sleeping or work hours.

Q/ Doesn’t the floor get uncomfortably warm when the system is working?

A warm floor with hydronic heating.

Toasty toes on a warm floor. It looks as if I should trim my toenails

No. In fact the floor remains at an almost constant temperature, which is only slightly above the room temperature, and always comfortable.  So comfortable, in fact, that I hardly ever wear slippers.

Q/ Under slab heating has become common in garages.  Is it necessary to have supplementary heat for fast recovery when large garage doors have been opened?

Actually, recovery seems to be faster than with conventional fan forced heat.  This is likely because less heat is lost through the loss of circulating heated air, and because of the large heat sink of the floor.

Q/  Do we need to place insulation under the floor?

Yes and no.  In the case of an upper level floor, the heating will need to be isolated from the space below with some degree of insulation.  R12 fiberglass seems to work well, and it is low-cost.   A reflective surface above or below the insulation may also be beneficial, but likely not critical.  Ordinary foil food wrap placed shiny side up is an economical approach. Some jurisdictions have building codes which require insulation under heated slabs.  Experience has shown me that this is largely a waste of money except in certain circumstances.  If the water table is within a couple of feet of the underside of the floor, then insulation may be beneficial.  It is, arguably, also beneficial if the slab rests on solid rock.  While reasonably dry dirt is not a good insulator, it is nevertheless an insulator, and you have an almost unlimited depth.  The difference in temperature between the earth and the slab is also not great.  In most places it is only about 20 to 30  degrees fahrenheit (11 to 22 degrees celsius.)  Of course, if you are building on permafrost it must be protected from the heat of the floor.  The extra heat sink provided by the soil can actually be beneficial, by aiding in recovery, and in case of system failure.  It is important that the foundation walls are well insulated to at least 24 inches (.6 meters) below the surface.

Q/  Can this or a similar system be installed in an existing home?

Yes, there are several ways it can be done.  It is not likely that it is cost-effective though.  You would, probably, be better advised to spend money on increasing insulation, and on sealing air leaks.  Even replacing windows with more efficient ones may be more cost-effective.

Q/ Could this be a DIY project to install?

Yes, if you have basic plumbing skills.  Electrical skills would also be useful.

Q/  What is the best heat source?

My preference is a gas-fired, high-efficiency, tankless water heater, although almost any source can be used.  The difference is largely in the control mechanisms.  Your choice would depend on what sources of energy are available, the level of heating required, and cost.  Because heating requires so little of the capacity of many tankless heaters, it should be used for domestic hot water as well.  This will ensure that it, at least occasionally, runs at full capacity and should reduce maintenance issues.

Q/  How large should a tankless water heater be.

In our climate, with incoming water temperatures at about 40 degrees F. (about 4.5 degrees C.), a tankless heater needs to be about 200,000 BTU per hour input. This will supply two or three hot water outlets at once.  The space heating needs of a modern well-built home, should require only a portion of this.  Since hot water needs are normally only for short periods, there should be plenty of excess capacity for this purpose.

Q/  Are there any situations where you would not use a tankless?

Some water can damage, or quickly reduce the efficiency, of a tankless water heater.  The water heater,  in this case, could be isolated by using heat exchangers and tanks,  which are less costly to replace.  It may be easier to use a boiler in a closed system. Water softeners,  Filters or other water purifying systems may be in order.  Water heaters are available with stainless steel heat exchangers, which may be a little less susceptible to corrosion, than copper.

Q/  Is a high-efficiency, condensing, water heater worth the extra cost.

If you use high volumes of hot water, I am sure it is. I am not sure the efficiency is as great for heating, as the heater will run at far below capacity, when in use for heating alone. The cost difference is not so much that I would be discouraged from going with a condensing model.

Q/  What effect has the choice of flooring have?

It doesn’t seem to make much difference.  My preference is for wood, laminate, tile or vinyl flooring. Carpet is not an advantage when the floor is always warm.  I am writing at my desk this morning, in a house coat, and with bare feet on a laminate floor.  It is minus 25 celsius outside with a minus 30 wind chill.

Q/  Can I heat multiple floors or separate areas with the same system?

Heating casn be controlled with a line voltage thermostat.

A simple line voltage thermostat.

Yes you can.  It may necessitate  more complicated system utilizing several zone valves or circulating pumps.  Separate pumps can be controlled with line voltage thermostats or with low voltage thermostats and relays.  Low voltage thermostats can be used to control zone valves which in turn will control pumps through line voltage end switches.  I will detail these systems in a my next post.

Q/ Where can I find parts and supplies?

Most of what you need can be found or ordered at local hardware stores at a reasonable price.  The more uncommon parts are available from plumbing supply and electrical supply sources.  You can often find the more unusual parts through the internet at dramatically lower cost.

Q/  How much piping will be needed?

I like to space pipe runs at 16 inches or less.  If more than 250 ft. of pipe is required, then manifolds should be used to provide several circuits. This is using oxygen impervious pex pipe designed specifically for hydronic heating.  Pex, or cross linked polyethylene, is not very conductive and is not efficient at transferring heat.  This does not affect the efficiency of the system at all, but it does mean that more piping is needed than with metal pipe.  More piping does mean a more even distribution of heat. Plumbers will sometimes tell you that glycol is needed for efficient heat transfer.  Once again, this does not effect the overall efficiency of the system at all and only adds extra cost and an element of risk.  Glycol is poison, and I do not want it anywhere near my water system.

Q/  Is placement of the pipe in relation to the floor surface important?

It doesn’t seem to be.  If in a slab, the depth of concrete over top of the pipe seems to be insignificant.  If in a joist space, it doesn’t seem to matter as long as the pipe is between the insulation and the under surface of the floor.  Expensive metal plates for heat distribution seem like a unecessary expense.  Simply fasten the pipe where it is convenient, and the least susceptible to damage.

Q/  Is this an environmentally friendly system?

As a rule of thumb, the most environment friendly system is the most energy-efficient.  Secondly the least use of material and whether that material is recyclable is important.  This system compares favorably with other methods. the use of natural gas as fuel releases the least pollutants to the atmosphere.

Q/  What about building codes?

If using a water heater for both domestic hot water and space heating, the most recent Canada codes I am familiar with, requires a circulation system to replace the water in the heating portion periodically. An alternative is to separate the heating and domestic with a heat exchanger and this is required in some jurisdictions. These are bigger concerns if you are using untreated water. Some authorities will even require a double wall heat exchanger so that a leak between will be visible. A double wall heat exchanger is much less efficient at heat transfer, and requires a much larger and more expensive unit.  North American codes in relation to this type of heat are still in flux due to unfamiliarity.  The biggest concern seems to be with legionnaires disease although I cannot find a single case that has been traced to single family residential heating . It is possible to route all water use through the heating system so stagnation is not possible.  I have used heat exchangers in mine and my sisters houses.  Do your own homework, in regards to codes, for your locality.

Q/  How hot should the water be?

I have found 140 degrees fahrenheit (60 degrees celsius) to give efficient heat transfer. This temperature also keeps bacteria growth low.  This temperature is easily regulated with a tankless. Most boilers need to operate at higher temperature for efficiency.  If using a boiler, mixing valves will be required to lower the water temperatures.  You may want to use a mixing valve, to lower the temperature for domestic use, if you have small children.

Q/  Are there maintenance issues?

If your water is hard, you will need to flush a tankless water heater with vinegar periodically, to remove scale.  This is a simple procedure that you can perform yourself with some garden hose lengths, a small submersible pump, and a pail with about 4 gallons of vinegar. How often this needs to be done depends on the water.  There is at least one in line water filter which may need to be cleaned if flow slows down.   With soft water at my last house, the heater required no maintenance in 6 years.  A forced air system requires filter changes several times a year at the least.  In case of failure, the various parts of a tankless, are replaceable with no need to replace the entire unit. Scale build up in a conventional tank type water heater usually means that the entire unit will need to be replaced.

Q/  What about safety?

A simple hydronic heating system.

The simple hydronic system in my house.

This is a low pressure, low temperature system that poses very little danger of burns or explosion. Temperatures are just high enough to restrict bacteria growth.  By using a direct vent system for the water heater, the chance of carbon monoxide release into the house is practically eliminated. There is no duct system to facilitate the spread of fire, smoke, or airborne pathogens.   No chemicals are used.  I believe this is one of the safest heating systems.

Q/  What are the space requirements?

From 4 to 6 ft. of a ouside wall should be sufficient.  A chimney is not required. The equipment can be located in a basement or upstairs mechanical room or in a crawl space.  In warmer climates it can even be located outdoors with minimal protection.

Q/  What happens if the system is meeting space heating requirements when you need hot water?

Domestic hot water can be given priority simply by taking hot water before it reaches the heating system.  I have never noticed a significant water temperature drop if the heating kicks in while I am showering.

Q/  What are the major advantages of this system?

No air movement to stir up dust and carry it around the house. The system is almost totally silent. Comfortably warm floors.  Using a tankless means you never run out of hot water.

Q/  what about disadvantages?

It is difficult to make quick temperature changes.  It may be difficult to find a plumber familiar with hydronic systems, or tankless heaters, if repairs are needed that you cannot perform yourself.

If you have any questions that have not been answered here, I will reply to comments. I will go into detail and include some drawings in my next post. I will discuss a couple of specific systems I have installed that are in use. Until next time

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One thought on “Heating with a Hydronic Radiant System

  1. rabradford

    God Bless you for this. There is so much crap on line, and most of it is just plain old stubbornness.
    How can I email you some questions I have to help me finish my system?


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