What is a Heat Loss or Heat Gain Calculation?
Heat Loss is the amount of heating BTUs (size of heating unit) needed to replace the heat lost from your home per hour during the winter months at a given OD design temperature
How are heat gains and heat losses done?
Does the heat loss or heat gain change with outdoor temperature changes?
Why do a heat loss or heat gain calculation?
If the unit is undersized, it will run a lot more than needed and may never heat the home, but use excess fuel. This is not as bad mechanically as cycling too often, but it will result in higher fuel bills.
Proper-sized equipment is less expensive than larger oversized equipment, so you start saving money right away. Any upgrades done to the home since it was built will reduce the heat loss, which is why we should do one anytime a heating or cooling appliance is replaced.
Is it common that my new heating or cooling appliance is oversized?
My contractor wants to install the same size appliance as the old one. Is that OK? It heated the house fine for many years.
More than 85% of the old equipment was oversized. It was the thing to do years ago when fuel was cheap. Most people have made their homes more energy-efficient by installing energy-efficient windows and doors. Updating insulation values and adding weatherstripping to reduce heating costs and improve comfort. This will reduce heat loss and require a smaller unit. A larger-than-needed unit will cycle too often, leading to higher fuel bills and reduced comfort due to more frequent temperature swings.
There are three ratings on gas and oil equipment. The first is input BTUs, the second is DOE Output or Gross Output, and the last is net ratings. If the contractor were to size the new unit based on the old unit's input and size, he would be installing even a larger unit than the original. Here is an example: 140,000 BTUs on the old unit running at 70% efficiency would be an output of about 98,000 BTUs. The new boiler, rated at 140,000 BTUs and running at 83% efficiency, will produce 116,200 BTUs. The new boiler would then be larger than the old, and some fuel savings would be lost. Size it properly with a Heat Loss or Heat Gain calculation. Any new piece of equipment should save you money. Size it properly and save the most money.
My contractor wants to size the new boiler by measuring the radiation.
As stated above, the same is true for the hot water heating units. The baseboard was typically installed on all exterior walls, exceeding the necessary amount when it was first installed and still exceeding the needed amount today. The advantage of using excessive baseboard and properly sizing the boiler is that the water temperature going through the baseboard can be significantly lower, requiring less fuel and improving comfort. At one time, heating systems were sized with a window cracked open at night because people thought it was healthier. Sizing the boiler based on the existing radiation will result in an oversized boiler, which will cost more to install, operate, and maintain.
The only time a contractor should measure the radiators and size a boiler with these factors would be a steam system or to calculate system water temperature when applying outdoor reset. Steam boilers are sized according to the system's square feet of steam, rather than based on BTUs or heat loss. We also do sizing for steam boilers. This requires different forms. (See pricing page)
You keep mentioning oversized equipment. Isn't it better to size the appliance larger?
What does oversizing an appliance hurt?
If I want to maximize savings, should I get multiple prices and make wise choices?
Unless it is an emergency installation, the answer would be no. You must give this some thought and prepare for the appliance replacement. To replace the appliance is fuelish! Plan a year or two if you don't need the product right now. It would be a lot wiser to have the heat loss done and see which improvements can be a better choice for your dollars.
What this means is to tighten up the home first. Let's reduce the heat loss first, and then replace the heating appliance with a smaller one later. The smaller appliance will cost less, use less fuel, and provide greater comfort. If you have 3" of attic insulation and add 6 more inches, is that a good move? Usually yes. When we do the Premium heat loss, we can make suggestions on where your money may be better spent. It may be wise to add insulation, new windows, and doors, among other measures, before replacing the heating appliance. Replacing the heating appliance now may not be the best financial decision. If the investment is larger for smaller savings or if it does not require changing the heating appliance size, it can wait. With attic insulation, there is a point at which adding more will not show a significant fuel savings. A heat loss can show this information. Please let us know, and we will break down the possible changes and show the resulting change in heat loss.
What is a modulating condensing boiler?
There is a gallon of water produced for every 100,000 BTUs of natural gas burned. This is a benefit of the condensing boiler. Operating at lower system water temperatures causes condensing to take place in the heat exchanger of the mod/con Boiler.
When fuel is burned, there is a chemical change and heat is produced. To keep it simple, mod/cons will remove more heat from the flue gases, causing them to hit the dew point. They then remove latent heat, which accounts for approximately 9.6% of the vent temperature. The water runs out of a drain line. This occurs when the boiler water is approximately 132°F or slightly lower, depending on the O2 or CO2 adjustment.
When the water temperature is above that in the boiler, the efficiency will decrease. As the boiler water temperature increases, efficiency decreases; conversely, as the boiler water temperature decreases, efficiency increases. These mod/con efficiencies typically fall within the 92% to 97% AFUE range. When the water temperature enters the boiler at 120F and leaves at 140F, these are the AFUE testing temperatures. When the entering water temperature drops below 120F, the efficiency can reach 98% to 99%. As the entering water temperature increases, the efficiency rating will decrease, possibly to 85% or 86%. The cooler these boilers operate, the more efficient they are. Lower flue gas temperatures at lower water temperatures result in fewer pollutants in their flue gases, making them a more environmentally friendly product. These products will normally supply you with increased comfort. The best application for these products is in large water volume systems, such as cast-iron radiators and radiant floor heating. Copper tube baseboard and hydro-air systems are less desirable applications, although they will still work well and maximize fuel savings.
With a properly sized appliance and home upgrades, is there anything else I can do for fuel savings?
What about Air Conditioning?
Again, the key is to avoid short cycling of the air conditioner or heat pump. To begin, a compressor is a relatively expensive investment. The fewer times you start, the better off your wallet is. As far as air conditioning goes, you need to run long enough to dehumidify the home. If the unit is oversized, it will run too short a cycle to dehumidify properly, and you end up with the cool, clammy feeling. If you walk into a home and it feels good to escape the heat of the day, and after a short time, you feel cool but still warm, like a humid, cool day, the AC is likely oversized. In a commercial building, this may be normal in the morning as the a/c is sized for many people and a hot day. As the day gets hotter, and people start showing up to shop or for work, everything balances out.