Furnace Motor Retrofit Offers Significant Energy Savings

Q: Can I benefit from a motor upgrade on my existing furnace?  If so, how much will it save me, and how much will it cost?

A: Most likely yes. The retrofit motors are 40% to 85% more efficient than many existing
furnace motors allowing those who run their furnace fan much of the time to save over $400 per year in electricity costs and over two tonnes of green house gas equivalents (GHG). Those who run their fan less frequently, or make heavy use of central air conditioning will see good good savings depending on the actual amount of time the furnace fan runs in a year. Those who only have their furnace fan run when the gas burner is also running will save less – I only run my fan while the furnace burner is running, and have calculated my own savings to be $23 per year and about 120 kg of GHG reduction. As for costs, the retrofit costs are about $500 for the ambitious DIY home owner, or $650 to have it professionally installed by a company like Rock Paper Sun.  It is certainly worth looking into, especially if you ever find yourself turning on “Run Fan” on your furnace, or if you have central AC.

Please contact us for any more details, to determine if the upgrade is suitable for your furnace, to order a kit, for more information or to arrange an install.

Why the upgrade. Most new high-efficiency furnaces include a “brushless DC” or sometimes called electronically commutated motor (ECM), which is much more efficient than the alternating current permanent split capacitor (PSC) motor that is in most of our homes, including most older high-efficiency furnaces. Historically it has been difficult to upgrade from a relatively inefficient PSC motor to a high efficiency ECM motor because the ECM motor requires different voltages as well as an advanced specialized control board, and these options were not available in a typical furnace. In recent years some companies have started offering retrofit packages which include strap-in compatible replacement ECM motors, and come with a fully compatible electronic control board to drive it.  This makes the retrofit/upgrade relatively easy to accomplish. Although many of these upgrades cost well over $700 for parts alone, Rock Paper Sun has found a reputable supplier which allows us to offer the kits as a DIY option for $495 or to complete most installs for $649.

Savings: A typical PSC motor is often only 50% efficient, or less.  They are however, relatively easy to build and do not require any (previously expensive) electronic controls to run. As a result, their use is quite wide spread for furnace blowers and many other applications. Although most of these PSC motors have multiple speed taps (i.e. different wires that allow the motors to run at reduced speed) there is often no, or very little energy savings realized with running at the lower speed. Also, because of the nature of the motor design, significant speed reduction is not possible.

For the ECM motor, efficiencies of over 80% are easily obtained, and because of the motor design, relatively low speeds are possible. Often best of all, reduction in speed is accompanied by a significant reduction in electrical power consumption. Historically the motors were somewhat expensive, but the reduced cost of electronic control systems coupled with the high volume of ECM motors being produced for modern high efficiency furnaces and blowers had allowed for a supply of very reasonably priced retrofit motors.

This SaskEnergy web page suggest annual electrical savings of $224/year based on continuous operation of the furnace motor during the winter season.

Typical PSC motor operation: Most older furnaces (high, mid and low efficiency) will have two fan speeds, high & low.  High is sometimes used when the “fan” switch on a thermostat is “on”, as well as when central air conditioning (AC) is running. AC units typically operate best with a high fan speed. The high air-flow makes the cooling more effective, and fast moving air feels cooler when us humans experience it – thus the phenomenon of wind chill. “Low” which is not really that low of a setting – is used for the main heating mode on many furnaces. This low speed is typically set to provide optimum heating performance from the furnace. It needs to be fast enough to transfer most available heat from the furnaces heat exchanger while minimizing electrical consumption as well as the wind chill effect.

Some home owners would like a 3rd “very low” speed if available. The purpose of this speed is for home owners wishing to have the fan on all the time, yet not wishing to cause wind chill, and wishing to minimize electrical usage. One common reason for running the fan when the heating element is not on, is to even-out the temperature throughout the house, especially bringing cool air from the basement or lower floors up to the main floor or to the 2nd level of a multi-floor home. Another common reason for running the furnace fan even when heating is not being provided is to utilize air filtration built into the furnace ducting, as well as to facilitate air flow for heat recovery ventilators (HRV).

Homes with central AC greatly bennefit from the ECM motor, because without it, the AC unit needs to provide extra cooling just to overcome the heat generated by a traditional PSC motor. With ECM, the fan motor produces much less heat itself thereby increasing the efficiency of the AC system.

Homes running the furnace fan 24×7 greatly bennefit from a low-speed enabled ECM motor.  The low speed setting often only consumes 60W to 75W of power, compared with 400W to 600W being consumed by the high fan speed of a PSC motor. It is this 325W to 540W savings multiplied by 24 hours a day operation that equates to multi-hundreddollar savings per year.

Some common questions:
Will the retrofit work on all furnaces?
Most, but not all. If you have a direct-drive PSC motor on your furnace now, the retrofit will almost certainly help. If your furnace has a belt-drive motor, or if your furnace already has a DC, or ECM motor, the retrofit is not for you. Note if you currently have a belt drive motor, you would most likely benefit greatly from a complete furnace upgrade! (Sorry, although Rock Paper Sun does the furnace motor upgrade, and numerous solar or in-floor heating projects, we do not currently do conventional furnace upgrades). If you are not sure what type of motor you currently have, we could come have a look for you, or may be able to determine from your furnace model number if you know it. You can review this 4 minute video – I apologize in advance for the video quality, you may need some Gravol if you are susceptible to motion sickness!

You mention the kit may be available as a DIY project, what is involved there? Yes, the kit can be installed by anyone with the tools and skills required to replace a conventional furnace motor. If we replace the motor for you, we take the opportunity to clean up much of the dust/debris that accumulates around the furnace motor and fan cage. We certainly encourage anyone replacing the motor on their own to also take the time to inspect other components for wear or problems, and to clean out the inners of the furnace while you have it open. We estimate the motor replacement will typically take 1.5 to 2.5 hours.

I understand the special cases discussed above, but what if I only run the fan while heating? In this case you will still save 40% or more of the energy used to run your furnace fan. If your furnace also has a combustion fan – the energy consumed by that fan will not be affected. In my case, I realized a 42% savings on the furnace fan, which translated to a 30% savings on my total furnace electric consumption. My furnace used to consume about 650 kWh/year @ $0.1167/kWh electricity rate = $76/yr. The 30% savings will result in a $23/year savings at the current electricity rate. Of course, if electricity prices increase, so will my savings. We find each home owner has a different way of determining if the dollar and/or GHG savings is worth the investment, as well as different expectations for future electricity prices.

Doesn’t all the electricity in the furnace motor just end up heating my house anyway? Yes, that is true. But currently natural gas costs about 1/5 that of electricity to produce the same amount of heat. So we are much better off to use electricity very efficiently for those things natural gas can not do, and use natural gas as our heating source. The GHG production associated with electricity in Saskatchewan is also considerably higher than the GHG production associated with even a low efficiency natural gas appliance. For the cases of running air conditioning, or just circulating air we often do not want to be providing any extra heat into the home. If you have an electric furnace (no natural gas) and do not have central air, there is very little incentive to upgrade the motor.

Other than energy savings is there any differences in motor performance? Very little significant difference. The replacement motor will be just as quiet as your existing motor, and assuming the same air speed selection is made, the air moving performance will also be identical. One minor difference is that the ECM motor has a “soft start” feature which means the motor spins up to speed  slightly slower than a traditional PSC motor, however it does this without the noise or power surge that is often common for motor start up. No more dimming lights, etc. when the furnace cuts in, and you receive a slight further reduction in power associated with eliminating the start-up power surge from the traditional motor.

We would greatly appreciate it if you leave a comment on this blog, or any related issue.

5 Responses to Furnace Motor Retrofit Offers Significant Energy Savings

Randy Engman P.Eng. says:

Great article. Now I wonder if one would be better off putting effort into Grid Feed solar? The simple payback for the retrofit is about 550/23 = 24 years. Grid feed solar beats this!!
The trouble with efforts that result in a reduction is that the law of diminishing returns applies. It takes increasing amounts of effort/$ to achieve a set benefit. But not so with Grid feed solar. Each additional panel results in an additional $ benefit. Keep up the good work guys, I’d still like to partner with you on Solar endeavors.

Cheers,

Randy Engman
Kelowna BC

    Brent Veitch says:

    Hi Randy,

    Yes, you make a good point, for those of us who only have the furnace fan running when the heating burner is firing, there are likely some other good places to spend our money 1st. One exception may be if you needed to service or replace your furnace fan anyway, at which time it might make sense to consider this ECM retrofit option.

    The better fit is for people who run their furnace fan more frequently. For example, we have done the retrofit for a customer who runs their furnace fan 24×7 for 7 months of the year. The fan used to consume 342W, and now the low speed ECM motor consumes 74W for a 268W savings.
    At 11.67 cents per kWh that translates to $22.52/month or $157 per year (with 7 months of operation).
    550/157 = 3.5 years, which is a very good ROI by most standards.

    By all means I agree that grid-tied solar is well worth considering as well!!

    Thanks a lot for taking time to add your comments.

    -Brent

Electric furnaces should be cleaned before the start of each heating season. Dirt and dust are the worst enemies of your furnace. Fortunately there are few moving parts and electric furnaces are designed for quick cleaning. The furnaces have no burners to clean or fuel lines to tend to.

Brent says:

I’ve updated the motor prices to reflect our current cost for the units. I have not updated any of the savings estimates to reflect the 5% SaskPower increase earlier this year.

Brent says:

After having the system installed in my own home for one year, my furnace motor monitoring shows that my furnace consumed 35% more electricity from May 2011 to April 2012 than it did from May 2012 to April 2013.

Aside from the different weather (the last year seemed longer and colder?) I also installed a Nest thermostat in Dec 2012, which may have helped with some energy savings in the latest 5 months vs. those 5 months the previous year.

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