Here’s a pop quiz for you furnace buyers: What’s the difference between two-stage heating and modulating heat? Should you buy a gas furnace or a heat pump for your house? Is there really much difference in efficiency between getting a furnace with 80% AFUE vs. 90% AFUE?
Don’t know what we’re talking about? Well, you’re not alone. You don’t have to be overwhelmed by the thought of buying a new furnace – it’s much easier than you think once you’ve done a little homework. To give you a leg up in your ‘studies,’ we’ve enlisted our HVAC specialist, Keith Hill, the technical support manager at Minnesota Air, to help you decide what furnace you should buy.
Think Of Furnace Ratings
By furnace ratings, we mean how efficiency is ranked. Keith says that companies have good, better and best furnaces that they manufacture – and he always recommends getting the ‘better’ or ‘best’ models.
Furnaces in those categories usually have the best efficiency and best warranties, he says. When looking at different models, pay attention to the percentage followed by the word AFUE – or annual fuel utilization efficiency. That number is the measure of how efficient the furnace is at converting fuel into energy – or fuel to heat your home. The higher the percentage, the better the efficiency.
For example, a 95% AFUE furnace may be the ‘better’ option over a ‘good’ (but basic) 80% AFUE model. And the ‘best’ would be a furnace that operates at a 97+% AFUE – because it’s even more efficient at turning fuel into energy than the mid-range model (and saving money on energy bills along the way).
Extra Features: What’s In Your Budget?
Once you know the efficiency you are looking for in a furnace, it’s important to also look at what bells and whistles you can afford. And we’re not talking about useless add-ons that just add to the price, but items that really provide more comfort, better airflow, quieter circulation, and even more efficiency.
“I’m a big fan of ECMs (electronically commutated motors),” says Keith. “These are very heavy duty motors that are controlled electronically, which makes them very efficient and very precise in providing exactly the right amount of airflow.”
He says the fully modulating ECM is the best, because it has a microprocessor that takes feedback from the motor and adjusts to give you more airflow when your filter gets dirty, and then changes again when you clean or replace the filter.
“It provides exactly the right amount of air during all conditions – heating and cooling – and can provide extremely low airflows for constant circulation,” he says. “So low that you will never hear it running.”
Also on Keith’s “must-have” list – staged heat or modulating heat.
If you’ve ever felt big temperature swings in your home – going from cold to hot and then back again – then you likely don’t have modulating heat, which works like cruise control for your furnace’s efficiency by providing a consistent indoor temperature. Staged heating works by keeping a lower burn in the furnace so you won’t have those big temperature fluctuations, too.
“It’s hard to explain the increase in comfort level, both in temperature and in noise levels when the furnace is operating in low fire,” says Keith. “Longer heating runtimes provide very uniform temperature control and since low fire requires less airflow, the noise levels are greatly reduced. It makes a quiet system almost silent.”
Keith says that with staged heating, a high heat is only required in very cold conditions, which means that the bulk of the season your furnace operates in the quieter low-fire mode.
“Modulating is even better as the heat will not shut off, just modulate down as the temperature nears the set point on the thermostat, then gradually increase as the temperature starts to fall,” he says. “In colder weather, a modulating furnace will run continuously. That sounds like it will gobble more fuel, but it actually uses less, since the furnace operates at lower firing rates, burning less fuel over a longer period of time.”
Keith says modulating is actually better for the mechanics of the furnace, because running motors, blowers, and other components more continuously actually allows them to last longer. It’s harder on motors and mechanical devices to start and stop frequently – as in a standard furnace – because that creates the most wear and tear.
Make sure to check out our other articles on everything HVAC, and you’ll ace any home heating test before you buy!