Our Summer (almost) without Hot Water Part II

Submitted by Barbara on Wed, 07/25/2012 - 20:11

In part I, we chronicled our process and lessons learned.  Here in part II we will try to process some of that information.

We decided we really dont want to live entirely without hot water, but how do we make it sustainable?

The Riot for Austerity goal is 100 therms per year.  After living with out our hot water heater for one month during the summer we finally have some idea how many therms we use for cooking & hot water and the news isnt good.  Of the approximately .6 therms per day we use during the summer, about half goes for cooking and half for the hot water heater.  That means we are currently using about 109 terms per year for cooking and about 109 therms per year for hot water.  Clearly the sum of these two is greater than the 100 therms per year and dosnt account for the modest amount of heating we do in winter either.  Its no wonder this has been such a stubborn category for us.

Possible strategies. 

Stove/Cooking:  Our total therms used for cooking was 9 therms per month.   I found online someone who estimated that their pilot lights were responsible for 40% of their consumption.  Each pilot might use between 1.2 therms (@ 40%) and 1.8 (@ 60%) therms per month.  Our beautiful old stove has 4 pilots, one of which has been off for years.  Turning off 2 more pilot lights would then save around 36 therms per year.  Turning off all 4 would save an additional 54 therms per year or around $55/year.  $55 can buy a lot of matches.  However I dont know what the foot print of a box of matches is vs. the footprint of 54 therms is.  Hmmmm.   Setting that aside, turning off all pilots would reduce our annual therms for cooking from 109 therms to 55 therms estimated.  That would reduce cooking from 109% to 55% of our total goal.

Water heater:  In our crazy pie in the sky world we use our really cool anaerobic digester & the sun to provide the majority of the heat but a pilot stays on to burn off the methane from the anaerobic digester.  If we could convert to a smaller pilot like that on the stove, it might use 18 therms per year.   Not too bad but there is a lot of work before we can get there.  In the near term, we might be able to turn on our hot water heater 1 day per week or rely only on the pilot light. 

Pilot only.  This stratagem involves turning off the burner and relying only on the pilot to heat the water.  It means you only get hot water maybe once or twice per week, then you must wait for the pilot to slowly reheat the water.   A water heater pilot uses around 36.5 therms per year or around .1 therms per day.  If we used this stratagem, it would account for another 37% of our goal. 

Another possible idea is to turn the hot water heater on 1 day per week.  If the pilot uses about .1 therm per day, keeping the water heater off 6/7 days would allow us .7 therms to heat the water on the 7th day.  Question is, will .7 therms heat the tank and can we remember to turn it on and off all the time?  According to Answers.com it takes .4 therms to heat 60 gallons of water from 55 to 140 degrees.  Sound promising if we can deal with the hassle of on & off.  Assuming all the math is correct, firing the water heater 1 day per week might use 21 therms per year.  An automatic timer can be purchased for a gas water heater, but in this case, the pilot must stay on in addition to firing the burner (.7 therm/week pilot + .4 therm per firing=?).  Converting to an electric water heater with an automatic timer would solve some problems but would bump our electrical consumption up.

Heating.  Over the two winter since we have installed insulation, we have averaged 43 therms (31 & 55 therms) of heating per year.  The illustration shows our heating load before insulation (blue & red) and heating load after insulation (green & yellow)  We hope to push this even lower, but will probably never entirely escape the need for back up heat from the furnace during the longest cold stretches.

Possible Totals.

Heating 43%, Cooking (no pilots) 55%, Water heater is then 2% or 2 therms by default. 

Nowhere in this plan do we have those types of numbers for hot water.  So what can be done?  Perhaps global warming will come to the rescue and the low end will become the norm for winter heating.

Heating 30%, Cooking 55%, Hot Water 15%

Almost there.  What about an electric water heater?

Heating 43%, Cooking (no pilots) 55%, Surplus 2%.  Adding an electric hot water @ 300 kwh/month?  Problem is, our goal is 183 kwh per month with solar panels.  We are slightly over 200 kwh per month so adding another 300 kwh isnt very attractive either.  It would however allow us to add a timer which would be an advantage even when we convert to solar hot water.  On the other hand, we would loose our methane burning pilot.

If we manage our ultimate dream of a hybrid hot water system,

Hot water 18%, Cooking (no pilots) 55%, remainder for heating 27%.  That almost seems comfortable.

Once again, there is no such thing as a free lunch but the sun comes close.  More time with the solar cooker, adding solar hot water is a must, more insulation for the house and possibly a HE wood stove. 

Now where did my doppelganger get off to?