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Furnace Efficiency

How To Make Your Furnace More Efficient

Make sure your furnace isn’t costing you money by running inefficiently.  Many efficiency problems need professional work to fix, but there are still some things you can do yourself. The most common problem reducing furnace efficiency is poor air flow.  There are many causes to low air flow, but there is a common symptom: high temperature rise.

What is temperature rise?

Temperature rise is the difference in heat between the air leaving the furnace and the air coming back to it. The label on your furnace should indicate an optimal temperature rise for your furnace, but generally it should be between 15 – 30 degrees C. If it’s above 30, your furnace is running too hot, and this is costing you money.

How to Test Temperature Rise in a Furnace

Professionals use specialized thermometers to test temperature rise, and there are usually small holes in the outgoing and incoming ducts for this. For you, a meat thermometer would work.

If no thermometers are available, a quick test to see for yourself is to adjust your thermostat up 5 degrees, and wait 15 minutes. Then lightly touch the outgoing duct on your furnace. It should be hot, but not painful or uncomfortable to leave your hand on. If it’s too hot to touch, this is a sign of high temperature rise. If your furnace has stopped running altogether in just 15 minutes, don’t even bother touching it – it’s running way hotter than it should be. (We are not responsible for any burns! Use common sense here).

How Does Low Air Flow Cause High Temperature Rise?

Too little air will keep the heat from dissipating quickly, causing this inefficiency.  Your furnace responds to cues from the thermostat, and will run as hot as it needs to in order to meet the set temperature (until a switch is flipped to prevent it from overheating).  If the heat can’t dissipate effectively, your furnace has to work harder to heat your home.

How To Increase Air Flow to The Furnace

Luckily, there are some simple solutions to low air flow before picking up the phone:
1. Change your air filter

This is very important to ensuring a proper air flow into the furnace, and maintaining good air quality in your home. Generally, you should change your filter once every 3 months. That is just a baseline. Homes with pets, lots of carpeting, or any other culprits of dust creation, will need to change it more frequently.

Another thing to look for is that filters hasn’t been pulled into the blower motor. This happens when the filter is not mounted correctly, or is not mounted at all. This has the combined effect of pulling fiberglass from the filter into the blower motor and of allowing dust particles into your furnace and home. It’s very easy to prevent but it is incredibly common. When you check your filter, make sure it hasn’t been pulled against the blower motor.

2. Are your air ducts being obstructed?

This is an easy fix. Make sure the vents providing air to your house’s rooms, and pulling air back to the furnace, are not closed or obstructed. Your furnace depends on this air flow, so don’t starve it and make it work harder than it needs to!

Make sure your ducts are properly sealed as well, as you can lose up to 20% of air flow if they aren’t. Small leaks that aren’t near the furnace (further than 6ft) can be patched with duct tape. If you suspect a larger issue with your ducts, you should consider getting them professionally sealed. It will save you money in the long run.

It is also possible that your ducts are not large enough to provide the air your furnace needs. Unfortunately, this is not a quick fix – but you might need to look into it.

3. Is your furnace in an enclosed space?

If you think of your furnace room as extra storage space, think again. Besides being a terrible fire hazard, your furnace needs a large volume of oxygen to run efficiently.  If your furnace room is full of your stuff, this volume of air is more limited. Less air available to pull into the combustion process means less efficiency.

Even with an empty furnace room, the volume is probably not enough. For every 20 BTU/hour (input) used by both your furnace and water heater, you need one cubic foot of empty space. With an 8-foot ceiling, a 60,000 BTU/hr furnace with a 40,000 BTU/hr water heater would need to be in a room with at least 625sq ft!

No need to get out the measuring tape – your furnace room is not that big.  You need proper vents to bring in the extra air from outside. For appliances operating at 100,000 BTU/hr, you would need at least 2 louvered vents, 10×10 inches each. One should be placed about 6 inches above the floor, and the other near the ceiling.