Is a High Efficiency Furnace Always More Efficient?
If it's time for a new furnace, you might be wondering whether you should replace your old standard furnace with a high efficiency model. And you know what? A high efficiency furnace might be your best choice...
Except when it isn't.
That's because some homes are simply better equipped for a standard efficiency furnace. What's more, designations like "high efficiency" don't tell the whole story when it comes to real-world operational efficiency.
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Got a vented attic or crawlspace? You might save more with a standard, 80% AFUE furnace.
All else being equal, a 95% AFUE (high efficiency) furnace is more efficient than an 80% AFUE (standard efficiency) unit. So yes, a high efficiency unit will use less energy and cost less to operate.
But installing the 95% unit might involve additional construction and modifications to your home's infrastructure. That gets costly.
If your furnace resides in a vented attic or crawlspace and you already have a standard furnace with open combustion, it's usually more affordable to replace the old standard furnace with a new standard furnace. Even with the lower operational costs of a high efficiency unit, you could save more money with a standard furnace since your home is already set up for it.
High efficiency furnaces do make sense when they're in sealed crawlspaces or attics insulated with spray foam.
Sealed spaces typically can't provide enough combustion air to properly operate a standard furnace. The 90%+ models are always a better choice in this case since they use a sealed combustion process that's suited to airtight spaces.
If you really care about efficiency, you've got to look beyond the "high efficiency" designation.
When considering furnace efficiency, you also have to consider the stages of heat available in a given unit.
- Most furnaces offer a single stage. They turn on, run at full blast, and turn off when they've satisfied your thermostat setting.
- More efficient furnaces offer two stages of heat. Most of the time, they run at the lower stage, saving the "full blast" stage for the coldest days and nights when they're working really hard. They turn on and off less often than single-stage units
- A modulating furnace is the most efficient type. It varies the heat output according to conditions, only running at the highest (and most energy consumptive) levels when it absolutely must. These furnaces run at lower stages most of the time and don't turn on and off very much.
What does all of this have to do with high efficiency furnaces, Well...
Some high efficiency furnaces only offer one stage of heat.
What's more, some standard furnaces offer two stages! By opting for a two-stage 80% unit, you still get a more efficient furnace even though the furnace is technically "standard" and not "high" efficiency.
Oh, and if that 80% furnace also contains a variable speed blower, you'll benefit during the cooling season as well. A variable speed blower runs for longer cycles than a standard blower, resulting in better humidity removal and lower electric bills in summer.
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