Once you have owned a home and weathered snow, ice, thunderstorms, and black-outs, you tend to take more notice to that piece of machinery we call a furnace.

A newly installed furnace can last 15 to 25 years, but when you use it close to six months out of a year, it is impossible to sit back and forget about it.

If you aren’t savvy when it comes to HVAC, it may be hard to know when your furnace is getting ready to die on you, and there is nothing worse than below zero weather without working heat.

You need to know whether your furnace is going to last for a while or if you should be looking for a new high-efficiency model for your home.

There are three things you should look at when determining whether or not to replace your furnace:

1. How old is your furnace, and how well have you cared for it?

If your furnace has been well-maintained, it should last 20 years or more. That is, it will last that long as long as it has been taken care of properly.

This means the filter has been replaced at least once every season, you have had it inspected by an HVAC technician every year, and you have checked and cleaned the fan and blower consistently. Furnaces that have been taken care of in this way can last 25 years. If yours has been neglected, it may have to be replaced within 10 to 15 years.

2. Will it be better to have it fixed or have it replaced?

The older your furnace, the more likely it is that replacing it will be the best option says FurnaceUSA Chicago. If your furnace is not very old, paying a few hundred to replace a broken fan would probably be worth the repair cost. But if the furnace is reaching the end of its lifespan, you may find that it is worth the money to replace it right now, rather than keep throwing money at the dying machine.

It can be challenging to determine which is the better option, but it will be easier if you know the signs of a failing furnace.

Is there a wide temperature difference between different areas of your home? If the problem is not bad insulation, it could mean you have a serious problem with your furnace.

How often does your furnace go on and off? If it cycles more frequently as time goes on, then your furnace has a hard time keeping the temperature of your home consistent.

Is it making noise? If your furnace is humming at you, it is shouting for help.

Have you noticed there is more dust on your furniture and gathering in corners? This may be because your furnace is blowing out dust and soot.

Once you sit down and add up the cost of the repairs you need, you could be looking at upwards of 1,000 dollars in repair work. That is 20 percent of the cost of a brand new furnace.

3. Is your furnace using more or saving more energy?

Keeping an old furnace running can mean much higher heating bills. Furnaces with an Energy Star rating have the rating displayed on the side. The SaskEnergy calculator you can find online can help you find out how much money you could save if you upgrade to a new furnace. The new high-efficiency furnaces are much less expensive to keep running than a model from 20 years ago.

When you replace your old furnace with a new model, you will not only save money on your energy bills; you will also get a warranty that covers 5 to 10 years on parts and repairs and a 20-year warranty on the heat exchanger. If your furnace is old by any standard, it is time to get a new one.