Here is our journey to upgrading our 40 gallon gas fired water heater to a 19 gallon electric one in July 2007.

Data From the 19 Gallon Elec. Water Heater

We've put our 19 gallon water heater onto a timer (electric, 7-day programmable - 2W power draw) and set it to only turn on for 1 hour before the price rise in the morning. This provides mostly enough heat (only a bath requires it to be turned on otherwise). If necessary it can be boosted by turning it on for 30 minutes during a mid-peak time period.

June, 2015 Update - Westek Digital Timer Failure

The Westek hardwired Digital Timer TMDW10CAN failed. Everything looked fine but the water heater was clearly not being turned on and the red light on the on/off switch would not turn on and one could not hear the relay click on or off.

Disassembling the timer was straight forward if a bit slow. The solder joint for the relay coil had clearly failed - a ring about 1mm from the relay pin was a clear sign of the solder joint failure. I was surprised to see this on the low voltage / power side of the relay. Re-soldering the joint fixed the problem.

March, 2013 Update

We are still happily using the system. When relatives visit we just leave the water heater on all of the time. Using a 240V timer and 240V heating element would allow the water heater to recover/heat up twice as fast but that's not a priority for us.

Somewhere in 2011 the original plug-in 15A timer failed. The socket into which the water heater power cord plugged started to get very hot, blacken the plastic case of the timer, and then failed. I replaced the timer with a wired in one from RONA - also rated at 15A - but now the connection from the timer to the heater element has much better electrical contact and we've had no issues. It's just not easy to measure the power draw now.

March 1, 2010 Water Heater Timer Energy Summary
Here is the summary of having our water heater on, and off, a timer. Note that a steady 2W power draw is from the timer.
Estimated daily losses (standby 0.6kWh, shower 0.2 and 0.6 kWh, dishes 0.15 kWh, laundry 0.3 kWh, bath 1.2 kWh).
30 days on a timer 1.19kWh/day average actual use, 1.29 kWh/day calculated average (-7.4%)
12 days w/o timer 1.45kWh/day average actual use, 1.16 kWh/day calculated average (+12.4%)
Summary: The timer saves us 20% of our energy use. Also - with the timer 30 to 50% of the losses were standby, indicating a need for better insulation.

Feb 2010 Water Heater Electricity Usage (using a timer so it turns on 5:30 to 7am):
average: 1.2 kWh/day
0.65 to 3.5 kWH/day (0.65 is standby loss, 3.5kWh involves bath, 2 showers, dishes, laundry load)

Jan 2010 Using a 15A 120V electronic timer (2W power draw) we've put the water heater onto a budget - it only turns on between 5:30 and 7am. As long as we don't use the bath we have enough hot water for the day.
Estimated Loss delta T = 49-18=31C or 110-61=50F, water heater is aprox 20" dia and 28" high = 28 sq-ft of area. 1W = 3.41 BTU/h, loss (BTU/h) = delta T * area / insulation. R = R8 "green foam" + R4 (fiberglas jacket) = R12
Estimated Heat loss = 117 BTU/h = 34W
Measured loss is 27W average but the temperature starts at 49C and drops over 23 hours so one would expect the measure loss to be less than the expected.

Dec 2008 we changed the water heater thermostat from 49C to 52C as it seems to have gotten a bit cooler. Over the next 46 days (with relatives visiting for xmas and again) our average use was 1.96kWh/day or 83W avergae draw at 52C. 20W is the standby draw at 49C; for a total of 103W average draw.

Nov 16, 2009 - Water heater elec use was 9.31kWh over 6 days or 1.33kWh/day with typical use.

Nov 23, 2009 - Water heater elec use was 16.72kWh over 13 days or 1.26kWh/day with typical use.

Our Problem Defined

Our original water heater was a 15 year old 1991 GSW 40 gallon natural gas model. It used $72/yr for the pilot light and an estimated $12/year heating water and the water inside was aprox 46C.

I have metered a 9 gallon electric GSW water heater and determined that it takes 25W ($23/yr) to keep the tank warm. The heater turns on 2% of the time to keep the tank at 50C. Draining water from the tank 2L at a time revealed that 40L of hot water could be removed from the 44L tank before the temperature started to fall.

Given what I knew of our water use (we never used more than about 20L of hot water at a time) we decided that a sub 20 gallon water heater can meet our needs. In the end we choose a 19L electric hot water heater because it was just big enough to provide hot water for taking a bath. If we didn't care about taking a bath the 9 gallon unit would have easily met our needs (except that they are less well insulated by default).

Water Use - Top Down Analysis

Metering the pilot on our water heater over a few minutes. The draw was 18cf/day ($0.40/m^3 or $1.10/ccf) $72/yr

Estimate water heating 3cf/day (based upon an average over 3 summer months), 6.25 ccf/mo or $12/yr

Water softener is manually regenerated every 8 weeks and it uses (mfg spec) 51 gallons.

HOT Water Use - Bottom Up Analysis

Here is our water use and estimated hot water use (assume 50% of water used is hot unless stated otherwise):
1.2m^3/month toilet (4L / flush * 10 flushes/day of cold water)
0.4m^3/month showers (6L daily, 20L one every 3 days)
0.3m^3/month washing dishes (est 10L/day)
0.3m^3/month hand washing (1/2L * 5 washes/day/person of cold water)
1.0m^3/month clothes washing (110L water (20L hot water), 2 loads/week)
0.25m^3/month baths (50L / bath, once per week)
0.15m^3/month cooking (5L / day cold water)

That totals to 3.9m^3/mo while we use 4m^3/mo.

It equates to around 1.1 m^3 or 10 US gal of warm water per day. That is about 7 US gal/day of "hot" water from the heater. Note that a hot shower is about 39C, while a cool one is 35C. With the water heater at 49C and intake water around 15C that means that we typically mix 70% hot water with 30% cold to get 39C. A typical American family uses 40 US gal of hot water per day.

Water Heating Options

  1. On Demand (tankless) These simply were not an option. Smaller ones do not heat enough water for some family members to shower with. The larger ones don't turn on with the amount of water I use when I shower. Either way the install cost was an estimated (phone quotes) $2,500 to $3,200 (Nichols $2700, Delta $2500+ one day to install, Conestogo Mec $2800 Rennai, Aire One $3200). Issues include not having an exterior wall to vent out as they run hot and require a stainless vent. The gas piping also needs to be large as these heaters use AT LEAST 4x as much gas our our furnace (40,000 btu vs 180,000 btu). Hard water deposits are also another issue.
    The heaters are $939 (Bosch 1600H NG) upto $1500 and Powerstar PS19T $679 and P528T $998
    The PowerStar PS19T is a 240V 19kW 2x40A that can manage 2GPM (9L/min) at +30C temp rise but the power draw is unreal. I'd need to basically wire in another 2x40A service for it.
  2. Home hardware has the Stiebel Eltron model which starts at 60A at 208/240 and it requires 0.29GPM or 1.1 L/min to turn on and has a programmable temperature. More powerful models require 2x40A or more.
  3. Electric Electric tanks have the benefit of being user installable and the smaller ones are easily put onto a switch or timer as well as being easily metered. Cost $250. Standby losses (60C assumed): 40W and measured at 30W (temp 49C)
    Note: Water heater sizes are US gallons by default
  4. Gas We could purchase a 33 or 40 gallon GSW gas water heater. Models now have an improved pilot that is 1/5 the size - but no more insulation. My own testing, and communication with both the mfg and installers all agreed that the primary heat loss is via the chimney. Replacing the water heater is $1k. Cost for the heater itself is $450+
    Rental fees are $10.80/mo or $130/yr for 40 gal gas and $15/mo for the power vent model while the high-eff Polaris one is $37.5/mo
  5. Solar This isn't really an option as the one local company which offered it was out of business and this "solution" only preheats water and can't be counted on to fully heat water in our climate.

Water Heating Variables

Pluses and Minuses

Electric tanks I can easily install. They work well with time day elec. pricing. Different elements 120V, 240V are readily available to allow for metering and putting the heater on a timer.

Gas fired tanks require a licensed gas fitter. They can provide lots of hot water; but there are no small tanks (smallest is 25 gal). Most of the heat losses are up the flue so there is no ability to insulate them better.

Heat Traps These are ways in which to stop hot water circulating within the pipe (convection currents) from sucking heat away from the tank. One way is via an s-bend in the pipe and another is via small balls which shut off the water flow unless there is demand. The ball method, however, makes a clicking sound when you start and stop drawing water and when I talked to GSW in 2006 they commented that they were removing these due to customer complaints about noise.

Anti-scald/Blending Valve

The Building Code in our area now requires a blending valve to ensure that the hot water temperature can not exceed 49C. However, in the mouse print of such devices you'll find that the inlet temperature to such a device must be 10C higher than the blended water temperature.

As we have for 15 years maintained our water heater at around 46C - having to raise the tank to 60C in order for the anti-scald valve to work is innane. This would increase standby losses by 25% (25% increase in temperature above ambient)!

I noted that the Building Code did not specificy that a blending valve was necessary; just that the max. water temperature must be 49C. In a new building here on campus (built late 2006) a water heater was installed without a blending valve (the water heater was set to 49C) and so we adopted the same "solution" for our home.

Calculations

Estimated and actual time to heat a 65L tank: 1.5h at 1400W for a 30C rise (19C -> 49C; so who needs a 3kW element?)

Heating costs (electricity is 1.5x as expensive as gas)
During summer 2007 natural gas is $0.413 cu-meter or $1.17/ccf and heater is 65% efficient. Elec is $0.09/kWh and elec. heaters are 93% efficient (Energy Factor) and 1 BTU = 252 cal, 1W = 3.4 BTU/h, gas holds 1,000 BTU/cu-ft, water rise is +40C (14C ground temp to 54C in the tank). Summer city water is about 19C, estimated more like 14C in the winter.

So the calculated costs to heat the 150L in a standard 40 gallon tank by 40C is:
Natural Gas 24cu-ft @ 65% eff = 37 cu-ft = $0.43
Electricity 7.0kW x 1 hour = $0.70 or 1.6x as expensive

Reality check a kettle heats 7c (1.75L) of water in 6.2min +80C rise takes 0.14kWh. So 150L at 40C rise would be 6 kWh or $0.60 in aprox 4 hours.

GSW Spacesaver 65L, 19 US gal Measurements

GSW Spacesaver 40L, 12 US gal Test


GHG (CO2) Emissions

Here is a web page to calculate GHGs for electricity and it works out to 0.94kg/kWh in Ontario. Gasoline is roughly 2.4kg/L CO2 and natural gas 1.9 kg/cubic-meter CO2

Car We drive aprox 8,000km/year at 8L/100km or 640L of fuel (aprox $640 at 2007 prices). That is 1,540 kg/year!

Electric Water Heater 0.5kWh/day to keep tank warm, aprox 1kWh/day heating water. That is 536kWh/yr or 504 kg/yr or 5.1 kBtu/day (kWh * 3.412 = kBtu)

Nat. Gas Water Heater $72/year (18cf/day to keep tank warm, $12/year (3cf/day) heating water. That is 77 ccf/yr or 211 m^3/yr or 400kg CO2/yr or 21.3 kBtbu/day (ccf * 101.3 = kBtu)
NOTE: CO2 emissions are done assuming that there are no losses in natural gas transmission from Alberta to Ontario - in reality they are quite significent and so the CO2 emissions are definately worse for the gas fired water heater.


Reliability

The anode should be checked every 3 years. After 15 years it was junk on our old tank.

Apparently the 6/9/12 year warranty on gas tanks is just a warranty - there is no difference between the tanks.


Total Family GHG (CO2) Emissions

Yearly GHG Emissions

For our family of four.

Pollution Source Consumption CO2 (kg/yr)
Pre 2008 Post 2008
Diet Whole-Food Vegetarian/Vegan
Car (1997 Ford Escort gasoline automatic) 6,000mi/yr at 34mpg 1,900 kg/yr
Car (2005 Toyota Echo std) 6,000mi/yr at 44mpg 1,500 kg/yr
Home heating (low eff. nat gas) 875 m^3/yr 1,660 kg/yr
Home heating (high eff. nat gas) 590 m^3/yr 1120 kg/yr
Electricity (BullFrog Green) 2200kWh/yr 1,700 kg/yr
Water heating (40 gal. nat gas) 211 m^3/yr 420 kg/yr
Water heating (19 gal Elec) 550kWh/yr 500 kg/yr
Total 5680 kg/yr 4820 kg/yr

The Passive House Standard

The Passive House standard sets a limit on heating energy as well as total energy use. An investigation reveals that they expect a very large electrical/cooking energy use to basically heat the house. This prevents the need for a furnace.

Great things about the Passive House are attention to details (thermal bridging) and earth tubes to pre-heat fresh air as well as triple glazed (Heat Mirror) windows and passive solar orientation. They are lacking thermal mass to really take advantage of passive solar heating though.

Comparing our 1991 home to the Passive House standard:

Passive House allows 120kWh/m^2/yr total energy use
Our home is 150m^2
Electric water heater is 100W average draw or 875 kWh/yr
  We used to have a gas fired water heater which was 211 cubic-meters of gas or about 2,300 kWh/yr
Our home uses 875 m^3 of gas (high efficiency furnace) for heating which is:
  875 m^3/yr / 2.74 = ccf/yr, * 101.3 = kBTU/yr, / 3.412 = 9,500 kWh/yr

So our total home energy use is 12MWh/yr while the Passive House standard allows 18MWh/yr and we
have 1/2 the insulation (walls, windows, ceiling) of a Passive House and no slab insulation at all.

To put that into perspective our existing gas furnace is 40,000 BTU/hr and runs 50% of the time on a windy -30C day - which is about 5.5kW continuous draw or about 4 hair driers. For the typical winter season leaving 3 hair driers running would allow our home to "heat itself without a furnace" but heating costs would be about 2x higher than they currently are ($950 vs $400).

Home PV vs Solar Water Heating


To grid intertie a PV system requires a $3,000 inverter; not the regular $500 one.
Standard Offer contract requires >2kW system.
Wind turbine would require a $1,000 tower which we don't have space to install.
The only PV option would be to partition our house and run part of it on a PV/battery
system which can be charged from the hydro grid as necessary (automatically?)

Our water heating is 2kWh/day or 2.6GJ/yr
Our home heating peaks at 6GJ/mo (typical, not extream).

By windows (passive solar).  Assume 6h light/day, 1kw/m^2 @ 30% eff
        Aprox 57kWh/day or 32m^2 of windows

Using Thermo tube system we need aprox 500 tubes or 50m^2 of collectors.
        Very roughly estimated at $50k

An 80 US gal (60 Imperal) water tank heated to 100C stores aprox
        70C * 300L * 1000 cc/L * 1J/C/cc = 0.021 GJ

So a large water tank holds enough heat for aprox 1/10 of a day!!

That seems wierd but it fits with what I've seen:

http://me.queensu.ca/people/harrison/research/solar/Images/Cruickshank_Harrison_CanadianSolarBuildingsNetwork_Sesci_2006.pdf

Now we know why homes use thermal mass and not hot water tanks.  Mind you
I've heard of open 1,000 gal tanks for heat storage!

The Ottawa group uses two 120 US Gal tanks.  One tank was not
enough for their system.  I'll get a copy of the CMHC report.

Ballparking the window size - a south-west facing home would be aprox
15m x 5m = 75m^2 so the window area required is 40% of the wall space
and that's on the large size from what I've read; about 2x too much.

Now coming at it from another angle.
50m^2 of space used instead for a PV array is roughly
10% efficiency, 1kW/m^2 => 5kW and aprox $50,000

So the solar hot water and solar PV costs per unit area are roughly similar.
The solar water heating is overkill most of the year while PV is useful year
round.

That's why you should exploit passive solar instead!!

NOTE: ground source heatpump would be about $25k for our home.

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