Home Heating Basics: Residential Boiler Systems
Home heating systems are an amazing innovation bringing comfort to families around the world. When the winter season begins, you immediately appreciate how convenient it is to have central heating. The heart of a heating system is the appliance responsible for producing heat. In most households around the US, this is either a furnace or a residential boiler. A furnace heats air which circulates around the home, while a boiler heats the water.
The working principle of a residential boiler is simple. The appliance heats water, distributes the heated water through pipes and radiators, then water returns to the boiler for the cycle to begin again. Different fuel types used for boilers include natural gas, propane gas, electricity, and wood.
To force hot water through pipes that circulate around the home, a boiler uses a pump instead of a fan or blower. There are some residential boiler systems that also include radiant floor heating. To control a boiler, the system includes a thermostat, an aquastat, and valves. These devices regulate water temperature and circulation.
For a more advanced heating system, you can also install zoning thermostats for individual rooms. Boiler heating systems can include additional features such as:
• Underfloor radiant heating
• Driveway heater
• Pool heater
• Towel warmers
These add-ons provide for a more luxurious and comfortable home but come with additional costs. In most cases, any additional feature may require renovations.
The efficiency of residential boiler heating systems
Residential boiler efficiency is also measured by the annual fuel utilization efficiency (AFUE) rating. Boiler manufacturers need to clearly display the AFUE rating of each product for consumers to easily compare the efficiency of each model. The energy-efficiency of a residential boiler is important because half of a home’s energy consumption goes to heating or cooling. You can easily compare high-efficiency, mid-efficiency, and low-efficiency models not only by the assigned AFUE rating but also through the features of the equipment.
Older, low-efficiency systems:
• Bulky and heavy heat exchangers
• Continuous pilot light
• There is a natural draft which creates combustion gas flow
• 56% to 70% AFUE rating
For mid-efficiency heating systems:
• There is an exhaust fan that controls the flow of combustion gases.
• Electronic ignition instead of a pilot light
• Smaller flue pipe
• Compact size and design
• 80% to 83% AFUE
While high-efficiency systems have the following:
• Condensing flue and secondary heat exchanger
• Sealed combustion
• 90% to 98.5% AFUE
If you currently use a low or mid-efficiency heating system, you are spending more than you should and produce more greenhouse gases. If replacing is not a feasible option because of the cost, you may consider retrofitting an existing residential boiler to increase its efficiency. However, this still depends on the compatibility and cost-comparison of retrofitting versus getting a replacement. If you have an older model that will soon reach its maximum lifespan, the sensible solution is to start saving up for a replacement.
Is a residential electric boiler efficient?
The fuel source is often the determining factor of a residential boiler’s efficiency and cost-effectiveness. Electricity is convenient and readily available anywhere in the country, but depending on where you are located, paying for electricity to fuel your boiler may be more expensive than other fuel options. Although new electric boiler models feature an efficiency rating of 95% to 100%, the price of electricity could make it a more expensive choice.
Features of a residential gas boiler
You can picture your central home heating system as a continuous loop of hot water coming from the boiler and moving through the pipes to reach radiators and revert back to the boiler. It is a simple enough mechanism to understand, but some homeowners still have a lot of questions about how to work and care for their central heating systems. What are the steps in the heating cycle of a residential boiler?
1. Natural gas piped through the municipal line enters the system through a residential connection.
2. The residential boiler will start burning gas and the heat exchanger transfers heat to water.
3. A pump pushes hot water through the pipe system.
4. Water flowing through the loop reaches the radiators. Radiators will emit heat and cooling down the water goes back to the boiler and the cycle repeat.
5. To control temperature and boiler operation, a central thermostat detects room temperature. When the room is hot enough, the boiler turns off. When the room is cold, the boiler turns on.
6. Combustion gases produced through the heating process exits a small flue.
For any home heating system, a thermostat controls the heating cycle. As such, it is essential to consider advanced thermostats with greater flexibility and control features. These days, you can use digital programmable thermostats which help save money spent on energy bills.
One distinct feature of a residential boiler heating system is the radiator. It is essentially a copper pipe bent back and forth creating a large surface area that disperses heat into the room. Some homeowners get confused and have the impression that radiators can operate at different temperatures. However, there is no such option with hot water radiators. Either the device is on, or it is off. What you can do is to control the amount of heat emitting from the radiator through the thermostatic valve.
These thermostatic valves connected to the radiator can be set high or low depending on the heating requirement for a particular room. However, a thermostatic valve should not be in the same room as the main HVAC system thermostat as the two will work opposing each other.
Another benefit of having a residential gas boiler is the option to use it as a water heating system. There are open-vented gas boilers that heat water in a storage tank while there are combi boilers that heat water instantaneously.
What is a condensing residential boiler?
All residential gas boilers combust fuel and produce gases as a by-product. These exhaust gases escape through an opening called a flue. Unfortunately, this basic design leads to a lot of energy loss. An alternative type of residential boiler, a condensing boiler, uses these combustion gases to heat up water coming out of the radiators. This process reduces the amount of energy consumed by the boiler. Condensing boilers may be highly efficient, but it is a more expensive and complicated system to maintain.
Boiler service and maintenance: common issues encountered with residential boilers
Every heating system has a flaw, and boilers are no exception. Before waiting to experience problems with your boiler, you need to schedule a maintenance service before the winter season begins. The following checklist will guide you on what to look out for and point out when the technician comes in for a routine check.
1. Check the pilot light. Simple issues like a draft blowing out the light or debris and dirt blocking the nozzle should be addressed. If the problem is more complicated, a professional HVAC technician can help you resolve it.
2. Check water pressure. A common cause of low water pressure is a leak somewhere in the system. In some cases, however, it could be something more serious like a faulty pressure relief valve. Either way, your HVAC technician should be able to determine the cause of this problem.
3. Thermostat issues. Inaccurate settings or problems with your thermostat may be easy enough to fix. In case of a damaged or faulty thermostat, replace it with a new unit.
4. Rumbling noise coming from the boiler. The rumbling sound coming from the boiler is also called kittling. This is not a good sign because it is a common indicator that there is a problem with the boiler. A professional technician will most likely clean the boiler to fix the issue. If the problem persists, it could be time to replace the unit.
If your residential boiler is already on its last legs, there are three things you should consider before buying a replacement.
• Size. The size of a residential boiler depends on the climate in your area. For a warmer climate, the size should be around 40 BTU per square foot. If you live in a moderate climate location, 35 BTU per square foot should suffice, while 50 BTU per square foot is best for cold climates.
• Venting style. Boilers with direct venting through a chimney is suitable for closed in areas. On the other hand, if the boiler features a venting style that forces air through the system, you need to locate the boiler in an open area.
• Efficiency. Around 89% of energy-efficiency is moderate enough. But if you are looking for more energy savings, always aim for a higher energy-efficiency rating of at least 90%.
Since you are investing in a new residential boiler, you might want to make energy-efficiency a priority. A high-efficiency gas boiler may seem slightly more expensive up-front, but it is certainly possible to recoup this investment after several years of use. Furthermore, high-efficiency boilers also have a longer lifespan.
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