Fall time is upon us and you might be thinking it’s time to replace that old furnace. So you call a couple of HVAC contractors to get you a quote. They show up and price out the job. As you are looking over the quotes to compare apple to apples, you notice the BTUs of the equipment are not the same between the bids. One guy has a 100,000 BTU furnace while another quotes an 85,000 and one a 60,000 BTU. What gives? Is the biggest furnace the best for your home? Is the guy bidding the 60,000 nuts? Should you just purchase the one in the middle and not worry about it?
The correct sizing of your new furnace is one of the most important aspects of your new installation and should not be taken lightly. Bigger is not necessarily better. A properly sized furnace will be quieter, more comfortable, last longer, be the most reliable, and use less fuel. Let me tell you why.
Quieter: Because a given size furnace must deliver a set amount of air – The larger the furnace, the harder it must blow, the more noise it makes.
Comfort: Each cycle of your furnace creates an up and down temperature swing. Usually you can feel this. For example, right before the furnace comes on you feel cold, when it goes off you feel warm. When your system is sized right, these cycles are much less frequent.
Longer lasting: An oversized furnace will cycle on and off much more often than a properly sized furnace. Frequent cycling wears any machine out. In regards to your furnace, it particularly stresses the heat exchanger.
More reliable: Wear and tear is caused with each on and off cycle. Each relay, gas valve, motor switch etc. must close and open with each cycle and there is only so many of these cycles built into each component before it fails. Compare it to city/ highway for your car. Stop and go city is much harder on all the components of your car than highway driving.
More fuel efficient: Any machine is most efficient when it is up and running. If you buy a 96% efficient furnace but it is oversized, the real installed efficiency may be below 80 % depending on how oversized it really is.
So as you have read, sizing is really important when choosing a new furnace. Don’t ever buy without a proper load calculation. To be sure one is being calculated, just ask to see a copy and have it explained to you.