Heat loss FAQ

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

Gain is the cooling BTU requirement (size of air conditioner) needed to overcome the heat of summer entering your house in BTUs per hour.

How are heat gains and heat losses done?

The whole house is measured room by room, or just possible the home perimeter, making note of window size, direction the windows face, type of construction, wall insulation, length, and direction of exposed wall. Any unconditioned walls, which are walls not exposed to the outside, but to unheated areas like a wall with a garage or sunroof on the other side. The amount of attic and floor insulation and the size of all exterior doors. All these measurements will affect the Heat Loss or Heat Gain due to prevailing winds and direct sunlight. The data is calculated, and the result is generated in total home BTU requirements or room-by-room requirements and equipment sizes.

   

Does the heat loss or heat gain change with outdoor temperature changes?

Yes, the heat loss or heat gain will change with outdoor temperature changes. The calculations are done for the average minimum and maximum temperatures of the area you live in. When a heat loss is performed, for example, using 13°F, we will achieve a specific heat loss for the home. Let's use a heat loss of 45,000 BTU/h. In other words, your heat loss at 13F is 45,000 per hour. Let's say today it has warmed up to 32F. The heat loss is less than 45,000; it may only be 30,000. Your heat loss does the opposite of outside temperatures. As the temperature outside decreases, the heat loss increases. When the outdoor temperature increases, the heat loss decreases.

Why do a heat loss or heat gain calculation?

Properly sized equipment runs more efficiently by cycling properly, thus saving fuel. Properly sized units will reduce maintenance costs by minimizing frequent starts and stops. If a unit cycles too often (heating up too quickly and shutting off again while the thermostat is still calling) due to being oversized, the rated efficiency of the equipment may never be met. The unit does not start at peak efficiency. It will start lower and work its way up to the efficiency rating of the manufacturer. In short, the larger the unit above the heat loss, the less efficient it will become.
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?

Yes, this is a widespread problem and is the number one problem in the heating and cooling industry today. The first step in efficient operation of the new heating or cooling appliance is proper sizing. The existing unit in your home usually is 100% or larger than
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 tightened up their homes 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 from the old unit and read the input and size from this figure, he would be installing even a larger unit than the original was. 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 more than needed 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 off the existing radiation will oversize the boiler and 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?

No, definitely not! As I mentioned earlier, regarding cycling times. It is imperative to size a unit properly. An oversized central air conditioning unit will run and cool the air, but the run time will be too short to remove the humidity properly. A unit too small will remove humidity well, but may not reduce the temperature of the house enough for comfort. An oversized heating appliance will heat the home OK, but it will cost more to run and maintain due to shorter run cycles. With oversized heating equipment, you may feel the temperature swing as the unit starts and stops.

What does oversizing an appliance hurt?

Over-sizing causes the heating appliance to run shorter cycles. This causes efficiency to be reduced. The shorter the cycle, the less efficient the appliance becomes. It could also run too long. The unit is efficient, but it may be too small for the heat loss. Properly sized units will run for 7 minutes or more. This saves fuel, increases comfort levels, and creates less maintenance. The starting and stopping of the equipment sucks life out of the controls and motors. It is better to run solid-state controls than to start and stop. The constant inrush of power will shorten their life.

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 out if you do not 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 get the heat loss lower, then replace the heating appliance with a smaller one later. The smaller appliance will cost less, burn less fuel, and create more 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, etc., 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 may not change 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. Just let us know, and we will break down the possible changes and show the change in heat loss when they are done.

What is a modulating condensing boiler?

These are newer higher efficient products. The gas input changes as the heating load changes. The appliance tries to match the heat loss as the outside temperature changes (see Does the heat loss or heat gain change above). This will help the product run longer, maintain a higher efficiency, and increase the comfort levels within the home.

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 is about 9.6% of the vent temperature. The water runs out of a drain line. This happens when the boiler water is about 132F or slightly less, dependent on O2 or CO2 adjustment.
When the water temperature is above that in the boiler, the efficiency will decrease. As the boiler water temperature increases, the efficiency will increase as the boiler water decreases. These mod/con efficiencies are normally in the 92% - 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 heat. 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?

Yes, we could suggest control strategies, which aid in reducing fuel consumption. These suggestions may include optional controls, such as simple outdoor reset, short cycle reduction controls, indoor sensors in addition to outdoor reset, buffer tanks, plenum heaters, etc. We may even suggest multiple appliances, depending on the application.

What about Air Conditioning?

Again, the key is to avoid short cycling of the air conditioner or heat pump. To start, a compressor is expensive. 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 equals out.

Does Comfort-Call have a sample of completed forms we will receive center>


Each Component, selections & SQ.Ft.     Condensed Form

Disclaimer: The information found on this website is for informational purposes only. All preventive maintenance, service, and installations should be reviewed on a per-job basis. Any work performed on your heating system should be performed by qualified and experienced personnel only. Comfort-Calc or its personnel accepts no responsibility for improper information, application, damage to property, or bodily injury from applied information found on this website.