Hot Water Heating

In floor heating solid state home inspections

No home is complete without some mechanism of adding heat for the winter months. Providing heat for our houses and condominiums requires an energy source and a delivery mechanism. For hot water heating, the water plays an active role as a heat delivery medium.

How Does Hot Water Heating Work?

Common hot water heating systems are made up of a boiler, water piping, circulation equipment, and distribution piping. Each component plays a key role in delivering heat in out homes:

  • Boiler - The boiler is the heart of the hot water heating system and is similar to the role of a furnace. The boiler controls the combustion of natural gas and transfers the heat from gas combustion to a water supply which is then circulated around the home to distribute heat. Unlike furnaces which activate when a thermostat calls for heat, most boilers attempt to maintain a constant temperature in the heating water by monitoring the water temperature going through the boiler.  As overheated water can be a safety concern, boilers have safety features similar to domestic hot water tanks to prevent and discharge any overheated water.
  • Hot Water Supply Piping - Piping is a complex network around a boiler.  They still need to be connected to the home water supply for initial filling and any replenishment. They need back flow preventers as the heating water cannot be allowed back into the homes drinking water. Heating water is re-circulated which means the piping needs to be in a loop at all times, even when individual 'zones' may not be calling for hot water. Water pressure is also a concern for the piping. Hot water heating systems operate at a very low water pressure level but with a common 'closed' heating system, the piping needs to handle pressure changes in the piping when water is heated and cooled. This is accomplished with an 'expansion' tank which acts like a shock absorber for the entire system. All this piping around the boiler can be very intimidating for hot water system novices.
  • Circulation Equipment - Hot water in the boiler needs to be mechanically circulated through all the piping in the system. This can be accomplished with one or more pumps that push (or pull) water through the system. Many hot water heating systems are broken up into 'zones' in the home with each zone controlled by a thermostat. The zones are activated or deactivated by either pumps or isolation valves in response to each zones requests for heat. When no heat is requested in the home, the boiler typically just circulates water through a short loop in the utility room to prevent overheating damage to the boiler.
  • Distribution Piping - Hot water heat distribution can be done through radiators, baseboard heaters, or in-floor radiant heating. In all cases, a 'loop' of heated water from the boiler is created and the distribution system transfers heat to the 'zone' in the home asking for heat. In floor radiant heaters are common on the Canadian West Coast and are often considered superior to furnaces as the heat provided is more even, it does not require creating an air draft, no room space is used for heating equipment, and the system is nearly completely silent.

Piping Concerns

Oxygen is the biggest enemy of a boiler system as oxygen in the heating water will rust out the boiler and other metal piping components. Preventing this rust is the reason hot water heating systems re-circulate the same water as once the initial oxygen in the water has oxidized, the water becomes 'inert' and won't do any further damage. 

Early plastic piping used for distribution, particularly in-floor radiant piping, was 'gas permissible' and it became a source of oxygen entering the heating system. The result was the weakest points in the boiler system would rust out and spring leaks in as little as 3 years after installation but certainly much earlier than the expected minimum life expectancies nearer 20 years. The worst culprit for piping was the bluish grey poly butylene piping which is also flagged for issues in domestic water use. PEX (cross linked polyethylene) has largely replaced all the other piping systems and has not been associated with any large scale issues.

Combination Heaters

With hot water needs for domestic use (showers, sinks) and water heating, it would make some sense to consolidate the water heating equipment in the home. This is not as simple as it may seem though as the heating water cannot be mixed with the domestic water for 2 very good reasons:

  1. Oxygenation - We don't want to introduce any new oxygen from the municipal water supply into the heating system water. Oxygen is also a problem for the domestic system but this problem is partially managed through a replaceable 'sacrificial anode' in the domestic hot water tank, plus, hot water tanks are significantly less expensive to replace than heating boilers.
  2. Non-Potability - Warm water is a breeding ground for dangerous bacteria like Legionnaires Disease. Domestic hot water tanks reduce the risk of bacterial growth as they constantly cycle in fresh water when operating, and even when left for a period of time, a minimum tank temperature of 54 degrees Celsius (130F) prevents the growth of any bacteria. In hot water systems, heating and cooling cycles may allow bacterial to grow for long periods of time. This water cannot be allowed to mix with domestic water or people could get sick.

To overcome the problem with combined water supplies, combination hot water heaters use a 'heat exchanger' to transfer heat between heating water and domestic water. The most common configuration for this is to run a loop from the boiler through hot water storage tank. An aqua stat (a water thermometer) measures the temperature in the domestic hot water tank and requests hot water as needed from the boiler to maintain a safe and optimal domestic use level.

The upside should be money saved on heating equipment and dual-purposing the energy used to heat water. The down side risk is that the costs of hot water storage tanks are not that high and the increased energy needed to maintain domestic hot water heat levels through the non-heating season will prematurely age the more expensive boiler system. That said, there are conditions where this configurations is beneficial.

What do Home Inspectors Look at with Hot Water Heating

Home inspectors are observing the installed equipment for make, capacity, and signs of deterioration or maintenance needed. They are also testing the system to see that it functions according to the operator controls.

As hot water heating systems can take hours to come up to temperature, it can be very difficult to test the distribution of heat in each zone when the system has not been in use for some time. Home Inspectors with Infrared cameras (FLIR systems) have an advantage here as they can detect rising heat levels perhaps hours before it can be detected without the equipment. Enquire with your Home Inspector about the availability of FLIR detection equipment as due to its costs, it is not yet a readily available piece of home inspection equipment.

Final Thoughts

No matter the type of heating system in your home, all heating systems require regular maintenance and testing by home heating contractors. Hot water systems present added risks from leaking components and overheated water and equipment should be tested before each heating season to help keep you, your family, and your home safe and solid.

By James Bell - Owner/Operator of Solid State Inspections Inc.