Clean Tech: My Dream All-Electric Granny Flat

9 Apr 2018

I am exploring how to make a granny flat my wife and I plan to build all-electric. We want to eliminate emissions from burning natural gas and take advantage of our solar rooftop.

Part of the plan may include upsizing our solar system to cover the additional square footage we’ll add.

So with a few home appliance upgrades and all electric addition, we may have a zero net energy home, or at close to it.

Households are responsible for 26 million tons a year of carbon dioxide emissions in California, virtually all of which comes from burning natural gas, according to the California Air Resources Board. That’s about 6 percent of total emissions. Add commercial structures, and buildings alone account for 11 percent of the state’s total greenhouse gas emissions.

The unit is being designed to be self-contained, with its own space heating/air conditioning system and water heater. This 350 to 400 square feet unit will have a small kitchen with room only for a single oven range. We’d like to include a stacked washer and dryer in the bathroom.

Fortunately, a sub-panel that will be able to meet the electric load is just feet from where the structure will be built as is a water supply line and for that matter a gas line too. All were capped years ago when we removed a spa structure. This will save us money, since new lines won’t have to be run. Since the unit won’t be metered, additional expenses related to upgrading our utility service seem unlikely to come into play too.

With financing just about approved and architect selected, I’ve been sizing up whether the cost of going all electric will be reasonable. I’ve been shopping for the needed devices and comparing the capital cost of electric options to the cost of gas options.

My research reveals that going electric makes both environmental and economic sense.

Heating/AC: For comparison purposes, I found a ducted Rennai gas-fired wall heater that runs a bit more than $1,100 that’s rated to heat the space we’re adding. However, then we’d also have to include a through the wall air conditioning unit. I would get an Energy Star certified unit, which is available from GE for about $400, plus the sleeve, which would cost about another $100. Let’s call it $1,600 upfront for the equipment.

However, since I’m going all electric and want something that’s quiet, I intend to go with a ductless mini split heat pump. I can get one made by Mitsubishi that’s an Energy Star model well sized to do the job for about $1,800, just $200 more than the hodge-podge of a through the wall AC unit and wall-mounted gas heater. The superior aesthetics and additional wall space to place furniture against is worth way more than the additional $200.

Cooking Range: I’d like a range with an inductive cooktop and a convective oven but the minimum price tag of about $2,100—after sales tax—for a GE exceed what I’m willing to spend. That boils it down to a more modest Energy Star gas range, which I can get for about $625 from Hotpoint, or an electric range with a four burner cook top and single oven. Frankly, I had trouble finding an Energy Star range, at least at nearby big box appliance stores like Pacific Sales, but found that I could get a Frigidaire for about $400. I don’t like conventional electric ranges since the burners take so long to heat up and cool down, but have decided to choose such a range for now to keep an eye on my total project costs. I intend to explore other electric options that could cost as little more, but have scratched the inductive model off my shopping list for now.

Dryer: My choice for laundry is limited to a stacked washer dryer unit or combo washer/dryer.

There were few Energy Star models available and little variation between the costs of the ones with gas versus electric dryers so the choice is easy. I’ve decided on a Frigidaire model that’s about $1,100 after sales tax and actually is $100 less than a comparable Frigidaire stacked laundry system that has a gas dryer.

Water Heating: I switched from a water heater with a tank to a tank-less water heater in our home many years ago. It’s a gas one and certainly saves on our SoCal Gas bill, but we’ve been disappointed by how much water we have to run before it heats up. Moreover, our water costs are rising again by another 50 percent after having doubled over the past decade.

Therefore, for our granny flat I’m going with a tank system. That makes the choice a no-brainer since electric water heaters with tanks seem to cost less than comparable natural gas models. I can get a variety of electric water heaters for well under $500, some even under $400. Comparable gas water heaters run almost $100 to $200 more, depending upon their storage capacity.

Conclusion: After my window and online shopping spree, I’ve learned that all electric residences in the inland valleys of Southern California are not only possible, but more economical than residences that rely on natural gas for many of their energy needs.

—William J. Kelly

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