Heat when the power is out. Use your furnace with an inverter.

Do you have problems with power outages and heat? Use an Inverter and battery bank to keep the heat running.

In Woodburn Oregon I have a problem with power outages. After several years of having power outages between 2 and 8 hours, and occurring 5 or more times per year. I wanted a UPS backup for my furnace, much like the computers, but would last longer.

I’m a DIY’er and I have family who are electrician’s and engineers to help me keep it safe. Think of this as a Kit that you hire a professional to install.

NOTE: If you have the money for one or two Tesla Power walls, those will work great and you get more options… You will need to figure out your own charging solution such as solar, generator etc..

WARNING – Disclaimer: Hire a professional electrician to install these parts, obtain licenses for electrical work, and be safe. You hold me and anyone involved with writing this article harmless for any damage, loss of limb, up to and including loss of life and property damage. AC Voltage is dangerous, DC voltage is dangerous. Again find a professional or call a local electrical contractor. Get ‘quotes’ on installation from one or more contractors.

My First set of Criteria for YouTube and blog post research;

  • UPS action like for computers.
  • Prevents abrupt power failure, brown outs to the natural gas furnace.
  • I could use alternate sizes of batteries in parallel for longer run time. Hours is preferred.
  • No internal batteries, but external battery bank support.
  • I’ve always heard to replace a UPS battery with a larger one.
    • Don’t – the UPS charger will mess up batteries of dissimilar types (AGM 1/AGM 2/ SLA/ GEL). And is sized for a tiny GEL battery.
    • 2nd Don’t – To get run capacity from Lead Acid, you need several, 3 12 volt 100 amp hour minimum for a Rheem High Efficiency Hybrid furnace sized for a 3000 sq foot living space.
  • Over sized AC watts output to support adding more AC devices if I wanted too, and so it can handle the load of the induction motors (fans) spinning up inside the Furnace.
    • There is a blower fan for the Natural Gas furnace exhaust and heat section.
    • There is a blower fan for the house to move air around and through the heat exchanger.
    • There is an igniter to start the fire in the heat exchanger
    • There is electronics in there.

I researched inverters to find one that met my criteria.

  • Auto switches between street power and Battery inverter mode.
  • Auto charges the batteries, maintain them through the life and use of the battery.
  • Supported a battery bank that I wanted to design, AGM batteries 100 Amp Hour (Ah).
  • Should charge at 50 to 100 amps per hour, preventing a long duration where DoD (Depth of Discharge) was minimized.
  • I wanted long run time, but not to buy 2 batteries at a time for a 24 volt system.
    • I choose a 12 volt system to keep it simple.
  • Runs between 1 or 2 days on battery for those really cold winter days and longer power outages.
  • Could recharge from a generator in extended outage, so at night it ran silent, during day was the noisy recharge cycle.
  • Solution should cost less than 2 thousand dollars.
  • Should shut off preventing damaging batteries.

Why choose this solution, over a generator, or standard cheap inverter?

  • Most generators that were inexpensive at the time 2018 are contractor grade, and had warnings “Don’t power sensitive electronics.”
  • Inverters that are cheap are not designed for electronics, insert noises into fans, and had warnings “Don’t power sensitive electronics.”
  • You can now get inverter generators. 500-600 watts of power can be dedicated for 10-12 hours charging your batteries, and have extra watts running your furnace, have enough power for a fridge and freezer and some LED lights. Then at night, the generator can go back to storage and not get stolen. Saves on gas! Gives you piece of mind.
  • You can run a generator all day, and store it without this UPS solution. That just seems like an inefficient use of gas that could be helping charge a large battery bank. Saves gas at night, and it is quiet at night. Offers more security at night. No worries.

After researching for about one month. I landed on this Inverter in 2018. I have had good experience with it for the past three years.

AIMS 2500 watt, 7500 watt surge Inverter Converter built in Adjustable Charger.

What about people/reviewers talking bad experiences of AIM’s inverters? Well I read what these people recommended and those other brands of inverters/converters also had issues. I have no idea on ‘rate of failure’ but there are far more favorable reviews for the AIM’s inverter I choose and it met my price point. Think of it this way. Almost all our electronics are made from China parts or in China. Get the extended warranty, and save some extra money for shipping the first 1 year warranty exchange which comes with the unit. In all probability if anything goes wrong, it does so in the first 90 days. My logic on this is, it has decent output for the price, and costs less than other units to setup and get running.

What about batteries?

  • Measure your system. Don’t guess.
  • This came from measurements using a Kill-a-watt plugin meter.
    • The furnace on high speed heat consumes around 800 watts.
    • On low heat it runs around 300+.
    • Fan Only (air circulating mode) is around 150 watts.
  • Lead acid batteries were the least expensive at the time, but I wanted it to last for years.
  • I choose some Lead Acid AGM 100 Amp hour batteries x 5.

Fuses? Battery Cables? Battery Monitoring?

  • 2×2 foot 1/0 0 AWG battery cables – x 2, one red and one black – from battery bank to inverter. Pure copper only.
  • 1 foot 4 AWG battery cables x 2 red/black x 4 qtty – between each battery
  • Fuse 400 amp

Lessons Learned;

  • Get a bypass installed to bypass the Inverter, a simple 15 or 20 amp light switch should suffice. I had to wire some AC bypass up during a storm just to have heat.
  • Get an auto transfer switch from street power to generator and a simple plug arrangement to run power directly into the inverter. Again I had to eventually AC wire something up that was temporary during a prolonged storm.
  • My big 3500 watt generator failed to run due to plugged carburetor. This was designed to power the house and the inverter from an input in my garage. This is what caused the previous two pain points for me.
  • Test run your unit to 50% DoD depth of discharge of Lead Acid Batteries, or 90% or better of lithium batteries.
  • The AIM’s inverter will run any Lead Acid Battery down past the lowest point you want.

2021-April-13 Update

An extended power outage of 5 days back in February this year 2021, and a generator that wouldn’t running left my battery bank in DoD at 1% or less. 10.5 volts or less for that period of time. Up to this point it was working fantastic for many hours. It ran our furnace when it was 32F and below for 23 hours till the AIM’s inverter shut off due to the batteries being dead.

Now the battery bank can provide 200 amps for about 12 hours reliably. After that it cannot provide the power it could. I purchased a Victron bluetooth 500 Amp shunt to keep power usage in check. With no LTE, WIFI or Cable internet during the February ice storm, I need to be able to measure the power.

The Generator solution I had failed. The generator failed to start even with starter fluid, it last ran in 2018. This is my fault. I got use to using starter fluid on all equipment the sat, I didn’t anticipate a problem running it. Another camping generator 1600 watts peak, 1000 watts running that is older did provide some power and charging assistance, but not at the power level I needed to really charge the batteries during the storm, run the freezer, and the furnace, and a few other essential items. We were able to save the freezer, but lost all the fridge food.

Since then we picked up an Inverter generator from Costco…. More updates on that soon.

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Bill Thompson

I am a mobile smartphone and embedded Linux engineer. I love to tinker with electronics and fly drones in spare time when not geeking out in a developers world!