Outdoor resets, good for the home, good for the environment
What is an outdoor reset?
The goal of an outdoor reset, such as the Honeywell AquaReset, is to increase the efficiency of a hydronic heating system. It works by matching the output of the gas or oil fired boiler to the heat loss of the building it serves more effectively. This is accomplished by the boiler control continually adjusting the boiler BTU output in response to the outdoor temperature via a sensor outside the house. So the colder it gets outdoors the hotter the boiler water temperature will be, up to the boiler high limit (usually 180°F). Instead of the boiler producing water at high limit all heating season it will adjust according in response to outdoor conditions.
Why is an outdoor reset necessary?
The analogy can be made that a hydronic boiler is very similar to driving a car. A car will get the best gas mileage when it is driven on the highway at a consistent speed. You wouldn't get on the highway and step on the gas to get up to 60 mph than slam on the brakes as you pass 60 mph then step on the gas again to get back to 60 mph. That is not an efficient way to drive. The same goes for a heating system, if the system only needs to keep up with the heat loss on a cool autumn day why should it run up to high limit, stop, up to high limit, stop. This burns up fuel and makes the home uncomfortable by producing more BTUs than necessary, resulting in temperature swings. It is more efficient to decrease the boiler output on not so cold days and have smooth, consistent heat production. This will burn less oil/gas and save money while maintaining a more comfortable living environment.
What is the benefit?
There are many benefits to installing an outdoor reset with you heating system. With resets like the Honeywell AquaReset, savings will be immediate and you may recoup your investment sometimes within the first heating season. An outdoor reset will also help in reducing temperature fluctuations in the home, resulting in a more comfortable living environment while lowering your homes carbon footprint.
Most resets, including the AquaReset, will allow you to set a warm weather shut down temperature. This will tell the control not to fire the boiler if the outside temperature is at or above a preset temperature of your choice. The benefit to this function is that if the temperature is above 60°F, for example, and you want to open your windows but forget to turn the thermostat down your boiler will not continue to run wastefully. As the night cools, and the outside temperature drops below the warm weather setting the control will come out of warm weather shut down and heat the house to the desired temperature. This is a great feature for landlords who pay for heat, as tenants do not necessarily think about the fuel bill.
Outdoor resets, every good hydronic heating system should have one.