Our Low(ish) Cost Backup Generator Setup

Today's topic is not one that is terribly exciting. But if you lived in Texas in February of 2021, maybe you are making similar choices to what I am discussing below. I'm writing this up because maybe someone out there is weighing some of these same options. I'm going to try to document the pros and cons of our specific setup, as well as some general things I learned along the way.

Some time around noon of 2021-02-15, our house lost power. It came back twice, for all of 90 seconds each time, until power fully came back some time on the 17th. Some parts of the DFW metroplex fared better, some worse. On the night of the 16th we stayed with family nearby who had rolling blackouts of 90 minutes on, 90 minutes off, which was more than enough to run their furnace to add some heat energy to their house.

But on the night of the 15th, we didn't know how long it would be out, so we stayed in our home. The living room has a large vaulted ceiling, and is the only room in the house with a gas fireplace. It turns out this fireplace was mostly for show, as very little heat from it radiated into the room. We did later see pictures on Facebook of people who had moved their couches closer to the fireplace and made a tent to trap more warm air, and some friends suggested that I should have used my camping tent to achieve similar results. We know that now for next time.

This was our sleeping arrangement that night:

The one really bright LED, TV, and internet equipment were being run by power coming from the 400W inverter in our van, burning through about 1/4 of a gallon per hour.

Whole House Generator

My extended family lives entirely in Texas. My parents live much closer to the Gulf, and the widespread outage was felt all the way down where they lived. They fared much better though, as they had installed a natural gas whole house generator a few years ago. Their purchase had more to do with hurricanes, and I doubt they thought they would end up using it during a winter storm.

They chose to install a Generac 24kW unit, which seems to be one of the most common units out there. These run around $5,000 for the unit itself, but installation can cost at least that much - running a gas line, wiring it in to the panel, laying a concrete foundation, plus getting HOA approval. These units run on natural gas or propane, requiring gas service to your house (which we have) or a very large propane take (not something many HOAs will allow). I've heard that the total cost after installation in our area can easily be over $15,000.

My understanding from my parents' specific installation is that they also pay a monthly or annual fee to have the company that installed it come out and service the unit annually to keep it in operational order.

The really nice thing about these units is that they pretty much run themselves. They detect an outage, turn on, handle the transfer from grid to generator, and run as long as they need to. Thy also do an automated self-test every week.

Portable Generator

We decided to go the portable generator route. This opens up a lot of choices - inverter or standard, fuel type, types of plugs, and most importantly, how to tie it in to the house's electrical system.

The disadvantage of going this route, one that I am ok with, is that there are a lot of manual steps involved to turning them on.

  1. Disconnect the house from grid power (usually via a big 200A breaker)
  2. Turn off all breakers
  3. Haul the generator out to somewhere outside, and place somewhere that its not going to get stolen
  4. Fuel the generator (or connect it to the NG line)
  5. Start the generator
  6. Transfer power via the interlock / backfeed breaker
  7. Gradually turn on load by turning on individual breakers

We ended up purchasing a Firman 7500W Tri-Fuel generator from Costco. It was on sale, delivery included, for $799. This unit can run off of gasoline and produce 7500 running watts, propane (6750 watts) or natural gas (5500 watts). It has a 14-50 plug for 50 amps** and 14-30 plug for 30 amp service.

We hired an electrician to install an inlet plug as well as a device called an interlock for right at $801. We also looked into getting a gas line installed, but that turned out to be more complicated and expensive than we thought.


Gas Line / Electrical Panel Placement

Even though we purchased a tri-fuel generator that can use natural gas, the layout of our house is rather complicated. The gas meter is on the opposite side of the house. I was hoping that some sort of T junction could be installed off of the water heater in our garage, but the plumber we contracted with refused to. Code requires that the gas line servicing one or more appliances have enough flow to fully supply all of the attached appliances, and running a generator and gas water heater simultaneously was not possible on that line. A new line would easily have cost several thousand dollars.

Some, but not all, of the houses in our neighborhood, have the gas service at the same location as the electrical service.

Limitations of a "Cheap" Portable Generator

Total Harmonic Distortion

The generator we purchased does have some downsides. It has a relatively high THD, or Total Harmonic Distortion. This means that does not generate a very clean sine wave. At a full load, the THD is 25%. A "good" THD is 5% or less. I don't plan on running my computer or even our TVs on this. If I need cleaner power for sensitive electronics, I can fall back on the inverters in our vehicles, which is what we did in the 2021 freeze. Or, 5 years from now, I could upgrade the "cheap" generator to an inverter generator. Right now a 7,000W inverter runs about 6x what we paid.

I've tested the generator with our fridges, some lighting, both furnace blowers and digital thermostats without any issues.

50 Amps?

This particular generator is rated to run at a peak of 9400W, or sustain 7500W. At 120V that would be 62.5A, and at 240V that would be 31.25A. For the peak of 9400W, that would be just shy of 40A. However, after consulting the documentation for this particular generator, the main circuit breaker that sits between the alternator and the 50A plug is rated at 31.25A. This breaker spans the two hot lines going to the 50A plug, so I think this means that two 20A loads could be pulled so long as they are on different hot lines on the 240V output. I need some clarification on this. Either way, I doubt this generator could power the smaller of our two ACs, which is protected by a double 30A (ie: 60A) breaker.

I could have purchased 30A cabling and utilized the NEMA 14-30 plug and inlet. This would have resulted in much cheaper cabling, or allowed for longer cable runs. A 100ft 30A cable is cheaper than the 25ft 50A cable I purchased, which would have allowed me to put the generator in a more protected location in our back yard.

In the end, the electrician convinced me to keep the 50A equipment should I ever choose to buy a bigger generator.

Bonded Neutral

This generator, and most non-inverter generators, tend to bond the neutral to the ground inside the generator itself. There is a lot of debate about this issue online. When powering a house, this results in a situation where there are two grounding paths.

I checked with my electrician. He suggested for a temporary, emergency use this should not be an issue. But, just in case, it turns out it is an easy modification to un-bond the neutral in this particular generator. I am not an electrician though, take that advice for what it's worth.

Worst Case Scenario

When deciding which route we were going to go - whole-house or portable - I had to think about what is the worst-case scenario that we could see here in DFW. How could February 2021 have been worse?

Several sources have said we were about 4 minutes away from an entire grid collapse, which could have knocked out power to most of the state for weeks or even months. ABC13 has a good layman's explanation about this.

So, the worst case scenario could have been the majority of the state of Texas being without power for weeks. Thankfully on the 21st the temperatures stayed well above freezing, up from the low of -1 at our house the morning of the 16th.

We had enough fuel in our vehicles that we could have made it to Oklahoma, which is on the Eastern grid, and could have stayed with friends or fueled up enough to get to family in Missouri.

The Plan Going Forward

I hope that this purchase turns out to be just a good insurance policy. I hope to only fire the generator up on a monthly basis to ensure that it is working well.

Should we see another February 2021, the plan is to use LP tanks to power the furnaces and a few key circuits. That would last maybe a day with intermittent usage. If NG service to the house is disrupted, we can fall back on 3000W of space heaters. That would take about 50% of the generator's rated LP output, and reviews of this particular unit says at 50% load it uses close to 0.9 gallons of LP per hour (a typical backyard BBQ tank is just short of 5 gallons).If the power grid and natural gas supply stays out in the region for more than a couple days, then a decision would have to be made - do we use the stabilized 5 gallon gas cans to power the generator and space heaters, or to fuel a vehicle to get somewhere else?

Real-World Tests

On January 8th, I gave the system a fair test. It was in the 50s outside, I opened the windows and let the house cool. I cut power to the house, hooked up the generator to propane and to the panel, powered it up and let both furnaces run for half an hour. I used about 1.2lbs of propane for that time.

A typical backyard propane take can hold about 20 lbs when full. So, assuming our electrical needs were consistent with my test (and that would be running two furnaces non-stop), we could potentially power the house for at least 8 hours. Realistically, it is probably closer to 12 hours per tank. I do not have a watt meter for the 50A/240V cable, but looking at the data from my eletrical company, I used an average of 1.45kWh per hour in the hours surrounding my test, but only 0.6kWh during the hour of my test. So 1.2lbs of propane was enough to provide about 0.85kWh, or about 1.4lbs/kWh.

On the day before we lost power, with temperatures between 10 and 23F, we averaged about 2.4kWh per hour, or 2.4kW continuous through the day. At that level of usage, a 20lb tank would provide about 6 hours of power.

Static Tests

As I do monthly burn-in / maintenance tests on the generator, I am trying to track the fuel and load usage to see how efficient it is.

Fuel TypeStatic LoadTimeFuel Used
Gasoline3.75kW (documented)12 hours8 gallons5.625kWh/gallon
Gasoline1.5kW58 minutes0.5 gallons2.9kWh/gallon

Total Project Cost

Prices here include taxes

Generator$880 (on sale)
50A Inlet Box$60
50A, 25ft cable$210
Interlock Kit (sourced by the electrician)$205
Electrical panel work and installation of inlet and interlock$596

Other Price Quotes

50A, 10 circuit manual transfer switch$385
Transfer switch installation$1,500
Natural gas hookup installation at gas meter (no long pipes)$900
30A Inlet Box + 100ft cable$200

Other Things To Consider

  • Gasoline does not store well. Even using fuel stabilizer, it is not supposed to be stored for more than two years. My plan is to rotate the fuel by putting it into our vehicles and refilling every few months.
  • Gasoline is also more dangerous to store. Propane tanks can leak, but the metal tanks are arguably safer than a 5 gallon plastic gasoline container
  • Remember the gasoline in the generator as well. Our particular generator has an 8 gallon tank. That gas can't sit in there forever. My plan is to never have more than a gallon in it, and I plan on testing it every month. The gas in that tank should never be more than a couple months old, and should have stabilizer mixed in with it.
  • Make sure that the loads are balanced. If using a 240V plug like a NEMA 14-50 or L14-30, there are two hot lines going into the two bus bars in the circuit breaker panel. Single width breakers in the panel are on alternating bus bars. Double width breakers span both bars. In our case, I made sure that the power to the furnace blower motors were on different bars. I've been told that having an unbalanced load - say 2000W on one bar, 0W on the other - is not good for the longevity of the generator.
  • Be aware of what local codes allow. One electrician we had who quoted the job would not install an interlock, because it was not allowed over in Dallas (or so they thought). They wanted to install a manual transfer panel. The second electrician we went with said it was fine by Fort Worth codes, which is where we actually live. The transfer switch and installation would have been about $1,000 more than the interlock and installation.
  • There are single-circuit transfer switches. If all you cared about was providing power to a single gas furnace blower, the total project cost with a smaller generator (or even a large vehicle-powered inverter) could easily be under $1,000. You could still provide power to fridges and freezers by alternating what is plugged in to the generator - using extension cords to get to the fridge when the furnace is not being powered.
  • Keep your generator away from your any occupied space (your house, your neighbors, etc). The picture below is too close, this was just for a quick test hookup. CO can seep in through any small opening and is not to be messed with.

2024 Followup

Since originally writing this post, we have only had to us the generator in a power outage one time. In April of 2023, a large transformer for our neighborhood went offline and needed to be fully replaced by the power company. It was out for about 10 hours. We ended up using the generator, plugged into the house, on and off for most of that day.

I do need to do a better job at maintenance. The generator should have an annual oil change, and I have not done that yet. And, even though I do have fuel stabilizer added, something in the system has not liked the fuel sitting in there between tests. But, I have learned that to clean it up all I need to do is let it run on propane for a few minutes, turn it off, and then run gas for a few minutes for a test.

I have measured my power usage, and if both furnaces are running at the same time, they consume about 1100W, or about 20W for the smart thermostats when idle. During a very cold day in January 2024, the two furnaces combined used about 11kWH across the whole day. Even if I needed to power the fridges or some computer/entertainment equipment, 7500W is overkill for what I am using this generator for.

I did have an AC tech measure the inrush amps on my AC's, and it does look like this generator could probably handle the smaller of our two ACs with NG, but that would be a stretch. I am not going to rely on having this as a backup to power the ACs during the summer months. At best, I can power the portable AC unit in my office, which uses about 900W when running.

I do wish I had saved a little bit by buying a smaller, lighter, and likely quieter generator and using 30A wiring. The tradeoff there might have been giving up the split-phase, and moving the circuits around so the furnaces were on the same leg in the circuit breaker panel. Also, since 2021, prices for solar and lithium batteries have continued to come down, to the point that I feel confident in making a small system with a 1500-2000W inverter, 12-24V / 200AH of lithium, and 1000W of used solar for under $1500 (a DIY version of an Ecoflow Delta Pro). Such a system would be the first line of defense.

2 thoughts on “Our Low(ish) Cost Backup Generator Setup”

  1. I live in the Allen/McKinney TX area, and bought the same Firman 7500w tri-fuel generator from Costco after the Feb ’21 Coldmageddon. We lost power for most of several days (the power came and went frequently, but never stayed on long enough to be of much help). Our swimming pool circulation pump and heater stopped. I drained the system which prevented freeze damage, though (our neighbors were not so forunate). Our gas range requires electricity to light the gas, but we were able to use a firestick if the power was out.

    Also, without the ability to run our home heating/HVAC, the fire sprinkler pipes in our attic froze. When thaw came and the power returned, the flow detector in our home’s security system sounded and we quickly discovered a waterfall fhrough our bedroom ceiling. Since my systems-repairman son-in-law was standing nearby at that moment, he quickly found the shutoff and stopped the water to the sprinkler system. Within a few minutes, many of our neighbors started experiencing the same situation. One of them was away, and incurred $90k in damages.

    I’m still working out how to integrate our generator. Will probably tie my natural gas feed into my dual water heater lines. We’ll be happy to forego hot showers and baths if we need to run the gen; but I would not be surprised if there is ample gas availability to accomodate the generator’s needs without depriving the water heaters on their occasional demands. I agree that pitching the tent indoors is a good idea for heat isolation if you are wihout power; also the little 12v diesel heaters look to be a good idea if you use that flex tubing to run the exhaust out an improvised window closure (and keep your CO detector nearby). But if able to run the generator, then it should be able to power the blower on the smallest of our home’s three HVAC (gas heating) systems.


    1. Thanks for the comment neighbor. I hope this latest freeze has found you warm. We actually had to stay with family in Allen a couple years ago since they had intermittent power and we didn’t.

      The one challenge we had with getting the generator tied in to the NG line was the size of the pipe. The one plumber I had look at it said it was not big enough to support both the instant water heater and the generator. I would be ok with having a valve or something to turn off the water heater if the generator was on, but maybe there is a code issue there. Regardless, it was not worth the money to run another gas line all the way across the house.

      I’ve since then been using an Emporia Energy Vue to monitor home electrical usage. Upstairs runs around 550W when burning, downstairs about 580W. Yesterday – the coldest day we’ve had in the past year – the upstairs unit consumed about 3.4kWH, the downstairs about 7kWH. I should do some more detailed tests, but Internet numbers are telling me that I should expect 3-4kWH per gallon of gas, so at 10kWH over a day, I should need conservatively about 3 gallons of gasoline per day just to run the furnaces.

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