A heat loss or heat gain is going to save you more money on your heating bill then just a rule of thumb furnace replacement. Are you planning to replace your home heating appliance to save fuel? Are you choosing the most efficient warm air furnace or hot water boiler to maximize your fuel savings? Are you aware that just replacing the appliance will not maximize your fuel savings? There is more to it than just sizing off the old unit or measuring the radiation or duct size. Do you realize that most equipment installed today is 100% over sized. This practice is a waste of fuel and increases maintenance.

Below is the top three ways of improperly sizing the appliance. When the heating or cooling unit is over sized it cost's more to install, short cycles which lowers the efficiency and increases the maintenance costs. All the below sizing methods will size the heating or cooling appliance incorrectly. The proper way is a heat loss or heat gain calculation.

1. Measure the existing radiation

2. Measure the square footage of floor space and multiply or divide by a magic number

3. Put in the same size as the one being removed

The above does not work!!!! The rules of thumb listed above always over sizes the equipment. The need for a heat loss today is critical with the fuel costs as high as they are and utilizing higher efficiency equipment.

Most consumers believe by replacing the heating appliance they will automatically save the maximum amount of fuel. This could be no further from the truth. In most cases, just replacing the heating appliance without a heat loss, a fuel savings will be encountered, but you will never maximize your fuel savings unless the unit is properly sized and properly installed. Choosing the right size unit is more than an educated guess or a rule of thumb calculation!

All areas of North America have a given outside design temperature. The reason for this is the greater the temperature differences between the inside and outside of your home the greater the heat loss. As the outside temperature warms up the heat loss is reduced. When the equipment is sized with a heat loss, it will heat the home with the lowest fuel input. As the outside temperature warms up the unit will start to short cycle. Longer run cycles are more efficient than shorter run cycles. To sum it up, the unit will short cycle when outside temperatures are warmer than design temperatures. These shorter cycles also will shorten the life of the mechanicals such as the motors and controls and also will require more maintenance.

With this known, imagine a heating appliance that is over sized. Let's assume we need 70,000 Btu's to heat your home at a design outdoor temperature of 10f, and the actual unit was improperly sized and is 120,000 Btu's. This unit is almost twice the required heat loss, and this is not uncommon. Statistics say that 85% - 90% of all units being installed will be over sized by 100% or more. When it is running the fuel input will be 120,000 instead of the 70,000, which is the actual heat loss requirement. This is the start of your problems. At the outside design temperature of 10f, the unit will short cycle. As it continues to warm up outside the short cycling gets considerably worse than if the unit were properly sized. Every hour of running time the unit will burn 50,000 btu's more than required on the coldest days. The unit becomes more oversized as the day gets warmer, the short cycling gets considerably worse. There goes your efficiency and wear on the motors and controls increases driving maintenance costs up. The fuel bill is higher than needed. Fuel is wasted every time the unit is running. Happy heating!

The proper sizing of the heating or air conditioning appliance’s will maximize the efficiency of the appliance. Let's assume we properly sized the hot water boiler and the old system had 1 thermostat (1 zone). We would get fairly good boiler efficiency. We then decide to break the system into multiple zones (thermostats). The properly sized boiler now becomes over sized as all the thermostats will not all call for heat the exact same time and they will not all satisfy the exact same time. The cycling of the different zones will overlap causing the boiler to short cycle reducing the boiler efficiency. The system efficiency will improve but the boiler efficiency will go down. There are a number of ways to control the boiler cycle rate. Here is a short list of things that can be done to extend the cycle time and increase efficiency, buffer tanks, Beckett Heat Manager, set point circulators, modulating condensing boilers and outdoor reset to mention a few. I would suggest run times of at least 7 minutes to peak your efficiency on cast iron boilers.

The system efficiency is as, or more important than the appliance efficiency. I don't want to down play the boiler or furnace efficiency but the distribution system and near boiler piping, duct sizing, etc I feel makes or breaks the total efficiency package. I have done jobs that had a properly sized 84% efficient boiler, and the fuel bills were still outrageous. We kept the same boiler and re-piped the near boiler piping. The fuel savings comparing btu's per degree day was 62% for the season. I had another job where the homeowner had an 88% efficient properly sized unit installed and saved a decent amount on his annual fuel bill. We added 22,000 btu's of baseboard to the system, installed a boiler bypass pipe and reduced the fuel bill by 9%. Purchase the proper sized appliance and get a good qualified contractor with a good understanding of systems to install and setup the appliance. This in no way discounts replacing the appliance with a newer more efficient one. A new appliance properly sized and proper near boiler piping should save between 20% - 50%

As in warm air furnaces, boilers come in a multitude of efficiencies. Boilers and furnaces that operate at efficiencies above 90% are called condensing, modulating/condensing or mod/con units. Most units operating in this range modulate the gas input, as needed which can create added fuel savings. Units operating below 90% are noncondensing units and do not modulate the fuel input. Mod/cons will try to match the heat loss as the outside temperature changes. What this means is the gas input will actually change. As the day warms up the unit will input less gas and if the temperature gets colder the unit will increase the gas input. The efficiencies on today's equipment will range from about 80% to 97%+. The higher the efficiency the less fuel used.

With all that said you should first upgrade the home with new doors and windows, add insulation, re-caulk and replace weather stripping if these areas have not yet been addressed. This will reduce the heating appliance size required which will lower your installation cost plus use less fuel and require less maintenance.

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