Larger Isn’t Better When It Comes to Heating Systems
America is the land of super-sizing. You get special deals like two-for-one, or BOGO, buy one get one free, or supersize your french-fry order. In most cases, getting more for your money is a good thing. However, if you are shopping for a new furnace for your home or installing a central heating furnace for the first time, a deal for a bigger furnace at a discount can be a costly mistake.
This happens much more often when people are deciding on the furnace for their home themselves and shopping for it online or in big box stores. They then install it themselves or hire someone to do the installation of the furnace and ductwork. Let’s look at an example of how this can easily become a problem. An Amazon search has these among many results:
If you’re trying to make a buying decision, this is American supersizing at it’s best. You can spend $8 less, get the same efficiency, but 20% more heating capacity. What could be better? Properly sizing your heating unit to the needs of the home would be far better. There are reasons for complicated heat loss calculations that determine the proper size of the unit to install.
From SensibleHouse.org, here is just a small portion of a very long explanation of the importance of heat loss calculations and proper sizing of your unit:
Heat Loss = Conduction + infiltration
There are two primary methods of heat loss in building, conduction thru the building envelope (ie the exterior surface: floor, walls, roof, windows, etc) and via air infiltration (or rather warm air escaping the building being replaced by cold outside air). Other factors, such as radiant loss/gain really only affect the temperature difference from inside to out. Those factors can be quite significant for short periods of time, and may even significantly affect the yearly amount, but are ignored here.2
Heat loss thru the envelope
The general heat loss formula is: Q=U*A*ΔT, or in plain words, the heat loss of an area of size A is determined by the U value of the materials and the difference in temperature between inside and out (that is the difference in temperature of the two surfaces, not the two air temperatures, which might not be quite the same. Below is an adjustment for air temperatures.)
If you just skimmed that, it’s OK. Only the professionals understand the calculations and their importance. Here’s why this is so important from a fuel and power consumption perspective.
It can seem to be a money-saving system that doesn’t run much, even on cold days. It comes on, runs for a short period of time, and the home gets warm. That is bound to save money, as it’s not using gas and electricity when it isn’t running. So, if the home can be warmed with shorter run times, it must save money. WRONG. Reasons why simplified:
The heat exchanger in the unit has a period of time when it first ignites to heat up to potential. That’s why you’ll often notice the burner comes on and there’s a short delay before the fan starts. This is wasted energy every time the unit starts, so the more cycles, the less efficiency.
The ductwork, even though it’s insulated, also requires time to heat up and the longer the unit runs, the longer the ductwork is operating at maximum efficiency. It’s wasteful for the unit to cycle on and off too much.
That 20% larger burner assembly in our example choices above requires 20% more fuel while it’s operating. It’s actually much more efficient if a properly sized smaller unit is burning lots longer that a larger one cycling on and off.
Considering these simplified explanations, it is much more efficient to have a properly sized unit. It also provides more even heat than a larger unit. The heat is more even and you’re more comfortable with the unit running instead of cycling.
No matter how you decide to have one installed, get experienced help in properly sizing the unit for your home.