So, your heating contractor suggests adding an “outdoor reset control” to your boiler and hydronic heating system. Would this be a good investment?
Outdoor reset controls are relatively simple devices that provide ample energy savings and a higher level of indoor comfort during the heating season. In fact, boilers equipped with outdoor reset can save homeowners up to 15-20% in annual energy costs!
What is it?
An outdoor reset control consists of three parts: an outdoor sensor, an element within the boiler’s main control, and a wire running between the two. The outdoor reset control “tells” the boiler what the actual, real-time outdoor temperature is. This allows the boiler to respond to the outdoor temperature by raising or lowering the boiler’s supply water temperature being delivered to your heating system.
You might be thinking, “But if the temperature inside the house always stays roughly at setpoint (the temperature you set your thermostat to) with or without outdoor reset, what’s the advantage?”
We’re glad you asked! To help understand the advantage of an outdoor reset control, it’s important to know that boilers provide the highest level of efficiency and longevity when they run at low input for longer periods of time. Low input means that the boiler is not operating at total capacity. When boilers run on low input for a longer time, they do not “short cycle.” Short cycling is when a boiler fires up to high capacity, heats the house (or zone) very quickly, and then shuts off. Boilers that short cycle utilize a lot of excess fuel!
To further illustrate this point, it’s also important to understand how a boiler was designed to “think”. Your boiler was engineered and built to supply your home with heat on the coldest day of the year. This is known as “design temperature”, and a boiler approaches each firing cycle as if it is providing heat under those circumstances.
If your boiler can recognize that it’s not actually the coldest day of the year (with outdoor reset), it can coast along at a lower capacity for a long period of time. If it can’t (without outdoor reset) it will assume the worst and will rapidly fire up, satisfy the call for heat, and shut down. When your boiler knows what the actual outside temperature is, you will experience significant fuel savings and protect the longevity of your heating system. It’s a lot like driving down the highway on cruise control with the engine running at 1,500 RPM, instead of stomping the accelerator to the floor and then hitting the brakes every few miles; one is going to provide maximum MPG and be easy on your car, the other is going to use a lot more fuel and apply unnecessary stress.
How do you get the boiler to remain at low-load instead of high-fire?
Temperatures outside your home have an effect on the temperature inside your home. During winter months, your home heating system responds to this by providing heat. This works efficiently on cold days, but inefficiently when it’s just “cool” outside. Unless your boiler knows what the actual temperature outside is, it will operate as if it’s the coldest day of the year…even if it isn’t.
Enter outdoor reset! When equipped with this discrete device, the boiler control reads the temperature outside and knows how to adjust the operation of the heating system accordingly.
Installing an outdoor reset control is only half the equation. Programming it is the other half. A professional heating contractor will perform a heat loss calculation of the home, taking different outdoor temperatures into consideration. Then they’ll measure all your radiation.
By doing this, the installer learns how much heat your whole system is delivering at a given supply water temperature, say 180°F as a maximum, and maybe 110°F as a minimum. This temperature is then compared to the heat loss results, providing a needed supply water temperature at a given outdoor temperature. The goal is to produce the lowest supply water temperature possible, while always providing enough heat to meet your thermostat setting. This means that the boiler won’t be “working as hard,” but it will be running for a longer period of time. That equals efficiency.
For you, the homeowner, very little. The boiler control already contains all the logic. Your heating professional will need to mount a small sensor somewhere outside the home (typically on the North side of the building, due to sun exposure). They’ll also need to run a small control wire from the sensor to the boiler. This can be pulled through a wall to avoid being seen in an occupied space, but as often as not, the wire can go right out the basement or mechanical room wall.
The use of outdoor reset controls is becoming more prevalent in the boiler industry every year. If your boiler already has outdoor reset capability built-in, the contractor may not even mention it to you. Understand that not all boilers are outdoor reset compatible. Older boilers usually do not have the capability to function with an outdoor reset control.
Rest assured that the outdoor reset control is a good investment. It saves fuel, creates higher comfort levels in your home, and helps your boiler last as long as possible!
Outdoor reset is available as an add-on enhancement to many of U.S. Boiler’s products and is your key to energy savings and enhanced home comfort!