Beware the Risks of Oversizing Your Furnace: Bigger Isn't Always Better

Most people tend to think of furnace installation as a pretty straightforward proposition. If your old furnace breaks down after 20 years of service, you buy a new one with the same basic capacity to generate heat and get on with your life.

Well not so fast, according to an article on Green Building Advisor. If you’re not careful you could feel colder much of the time, even if your new furnace generates more heat than your old one. Sounds strange but it’s true.  According to the article, this is what happens when you replace an old 60,000 BTU furnace with the more efficient 69,000 BTU furnace the HVAC tech talked you into.

“The relevant capacity of the furnace isn’t the rate of BTU input. It’s how quickly those BTUs go into your home — the output capacity. Let’s look at what happened… when you replaced the old furnace. You started with 60,000 BTU/hr at 80% efficiency, so your old furnace supplied 60,000 x 0.8 = 48,000 BTU/hr. The new furnace has an output capacity of 69,000 x 0.95 = 65,550 BTU/hr… So, your new furnace is 37% larger in terms of its ability to provide heat to your home.”

The reason this matters is that with all those extra BTUs available the furnace is going to kick out shorter, but much more intense bursts of heat, meaning you’ll be frying like an egg on a red-hot skillet for short periods and bundling up against drafts much of the rest of the time. Makes sense doesn’t it? So why would any HVAC technician worth their duct tape recommend such a furnace installation?

First, not all HVAC technicians are equal. Some are highly-trained experts with years of hands-on experience who keep themselves well-versed in the latest technological advances surrounding furnace installation and are always straight with customers. Others… not so much.

And second, because HVAC scams are more common than many in the profession would like to admit. That’s understandable as frauds tend to give everyone a bad name. But if it’s going to be stopped the phenomenon first needs to be recognized. So here’s our crib-notes version of the HVAC scams list over on buildings.com which you should check out if you have a few minutes.

• • The “You need a new one” scam – If you’re being advised that you need to replace a vital and expensive part of your furnace take a minute and think it over. Is everything pretty much running the way it always has? If it is take a pass on the replacement part.
  • The super-size me scam – This one speaks to the article on green building advisor. Since you buy your furnace from the HVAC contractor who does the furnace installation you need to remember it’s in their interest to sell you the most expensive one possible.
  • The ghost parts scam – The tech identified the problem and reports he replaced the offending part. You paid a pretty penny for that part but later discovered the problem is still there. Insist on seeing any parts that have been removed and replaced.
  • The “It’s tune-up time” scam – If you’re paying to have your system tuned up every season, or even twice a year you’re being taken. It’s almost never necessary to do maintenance on an HVAC system more than once a year.

As we said, check out the full list over at buildings (.com) when you have a chance.