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How to figure Volts-Amps-Watts
for residential water heater |
Use only 600 volt wire. Lamp cord, extension cords are not rated 600 volt. Use copper wire only. Aluminum wire is fire risk and should be avoided or installed by professional. 30 amp breaker use 10 gauge / 120-240 volt 30 amp outlet can be installed on 30 amp breaker only/ use 10 gauge wire ... cannot be connected to 15-20-40 amp breaker. Orange/ #10 gauge wire, with ground ... 30 amp capacity. Safe maximum: 30 x 80% = 24 amps. Buy: 10-2 gauge/ 30 amp 10-3/ 30 amp Southwire electric tools |
Yellow
12 gauge 20 amp 120 volt 20 amp outlet can be installed on 20 amp breaker, but not 15 amp breaker/ use 12 ga wire. ... cannot be connected to 30-40 amp breaker. 1 Yellow/ #12 gauge wire, with ground ... 20 amp capacity. Safe maximum 16 amps. Buy: 12-2 gauge/ 20 amp 12-3/ 20 amp NMB is house wiring UF is underground Rolls of stranded wire HOOK UP Wires |
Multimeters Voltage is tested across two separate wires. Ohms or resistance is tested across both ends of same wire. Amperage is tested along one or two points on same wire. Buy: Analog multimeter Multimeters at Amazon Klein multimeter Electric testers at Amazon Clampmeter for testing amp flow on line |
Electrical tools must be insulated. Always best to disconnect power, but insulation failure, lack of proper grounding, grounded neutral, lack of GFCI, out-of-code wiring, generator operating without transfer switch, and other problems still pose a risk to anyone working on electric power ... even when breaker is off. Buy: 1000 volt Tool kit Electrician tools kits KLEIN TOOLS Tools kits IRWIN tools KNIPEX Telephone cable knife Low Voltage Mounting Bracket for Telephone |
Protect wiring from damage Use nipper instead of pliers or screwdriver for removing staples (and nails). Do not damage cable or wires inside cable. -Code says: Cable SHALL BE secured without damage to the outer covering. NEC sec. 336-15 Buy End cutting nippers at Amazon |
Electrically insulated tools When removing insulation from wire, do NOT score or put cuts on surface of copper wire. Doing so increases resistance and heat on wire and creates possible weak point. Buy tools: KLEIN TOOLS Wire strippers at Amazon Electric Wire Stripping Machine Linesman pliers Utility knife at Amazon |
Weatherproof
lever switch on outdoor lights Safely operate outdoor toggle switch Replaces outdoor cover Install over top of ordinary switch Works with single-pole, double-pole, 3PST, 3-way, 4-way switches etc Use weatherproof box for outdoor Can be used indoor or outdoor Buy: Cantex lever switch Leviton lever switch Outdoor lever switches at Amazon Resource Cantex-toggle-switch-covers.pdf Cantex-PVC-junction-boxes.pdf |
Weatherproof wire connectorConnector cavity is full of siliconeBuilt-in cover keeps silicone in place Protect from water, dust etc Buy from my affiliate links Weatherproof size 14 to 6 Amazon Weatherproof size 22 to 8 Amazon Resource How to select and install connectors |
Multimeter Test for breaks in wire/ Test for voltage Most appliance require 80% rated voltage to function correctly Buy Analog multimeter Multimeters at Amazon Klein multimeter Electric testers at Amazon Clampmeter for testing amp flow on line Resource: How to test and replace element How to test thermocouple Element tests for 120 volts How to test wire |
Safety when testing wires: Never touch wet or previously flooded appliance. Never stand on wet surface when working on electric. Never stand on bare soil, put down dry boards. Tape tester leads to wood sticks to keep hands away from power. Use non-contact voltage tester before touching wires. Never touch or lean into any made of metal. Remove metal objects from pockets. Do not use oxygen or fuel accelerants in same room as electrical repairs Resource: Basic house wiring |
Look
for label on side of water heater / or any
appliance Residential water heaters with 2 elements are rated 208-240Volt Homes in US and
Americas are usually wired for 120 / 240Volt Basic electric wiring
Condo buildings, apartments can be wired for 120 / 208Volt Ordinary residential water heater will work with any voltage, up to 480V ... including 120, 208, 240, 277, 415, 480 volt* ... this is possible because the mechanical thermostats are rated 480 volt and because elements are resistive. *This is possible as
long
as voltage
does not exceed the voltage rating printed on end of each element.
CAUTION .... water
heaters
with electronic controls such as heat-pump, energy smart, tankless,
demand-response heaters, factory-made
solar units etc must be connected to the rated voltage and no
other voltage.
A water heater that is rated for 240-208 volt can be connected
to 120 volt
generator, and heater will function but heat more slowly ... this is
possible because elements are resistive ... and 120 volt is less than
the 240 volt element rating printed on end of element. Connect heater to generatorResources: Connect water heater to generator Review heat pump Review Solar glycol water heater See inside main breaker box High voltage solar PV Low voltage solar PV Commercial 3-phase water heater |
Larger image |
Look for Volts
and watts shown on end of element When replacing elements, use same Wattage shown on tank label If using smaller wattage, tank will heat slower. For example changing from 4500 watt to 3500 watt will cause tank to heat more slowly. Same temperature water will still be available, and smaller wattage will not void product warranty. Smaller wattage can last longer if water is very hard and elements burn out frequently. Tank warranty is voided if you install higher wattage element than shows on label Higher wattage element can be dangerous if wire size and breaker do not match load. Best to match element wattage with tank label. Generic hardware store elements are good choice. |
Typical electric water heater label See larger image See another image Always test actual volts at your home first, because that affects actual watt output of elements. -If household voltage is 236 instead of 240 volts, then there is a tiny difference. -If household voltage is higher at 250 or lagging at 215, then these voltages can affect 240 volt household appliances, causing malfunction. With electric heater, higher voltage can burn out elements, and lower voltage give less hot water. Buy: Multimeter Resource: Is US electricity 110-220 volt or 120-240 volt?... it's 120-240V |
Look
for Volts and Watts on label Label shows Phase: -Phase 1 or
single-phase is household or condo
electric
service
-Phase 3 is strictly a commercial service, and shows on some commercial water heaters, which can be converted to single-phase. Resource: Commercial 3-phase water heater Label shows 208-240 Volts ... heater can be connected to either voltage, but cannot be connected to higher voltage such as commercial 277, 415, 480 etc. Each element is 5500
watts @240V
Total connected wattage means both elements are never ON
at same
time.Or elements are 4125 watts @ 208V If total connected
was 11,000 watts, this would indicate a special-order simultaneous
heater.
Note about 208 Volt: 5500 Watt rating drops to 4125 watts when tank is connected to 208V. Why? Water heater elements are like light bulbs... When power drops, then light bulbs dim, and produces less wattage output. Same with elements: when voltage drops, the element is less hot and wattage output is lower. Resource: Tank wiring can be changed: How to wire thermostats and elements Off peak water heater wiring Convert 3-phase non-balanced water heater to single-phase How electric water heaters work What is 208 volt Difference between single phase and 3-phase |
See larger image |
Different
water heater label/ 4500 watts @ 240volts Label shows 4500 watt elements @240Volt Total connected 4500 watts, which means both elements are never ON at same time so the maximum wattage consumed by this water heater is 4500 watts. Houses, and ordinary apartment buildings have 240Volts While commercial apartment buildings and businesses might have 208Volt service Resource: What is 208 volt Note: 4500 watt element @ 240V changes to 3375 watt element @ 208 volts Watt rating drops when voltage drops Always test voltage first before figuring watts Resource: How electric water heaters work |
Other
things on label Serial number/ which contains code for date of manufacture/ Gallon size of tank Manufacturer brand Number of warranty years. Warranty is usually from date of purchase. Lacking sales receipt, the warranty reverts to date of manufacture, which might be several years before purchase. Warranty usually covers tank + parts + labor first year, then tank + parts following years. Resource: Find age of water heater Water heater manufacturers |
Elements | |
Larger image Volts and watts are printed on end of each element 480 volt 4000 watt or 415 volt 3000 watt When voltage drops, the element wattage also drops Typically
480 volt is common on 3-phase non-balanced commercial water heaters.
The non-balanced 3-phase heater can be converted to single phase but
attention must be paid to the element voltage and wattage
Resource: 3-phase non-balanced / and conversion to single phase |
How to
figure resistive wattage by volts Ohm's laws says: Volts squared ÷ watts = ohms NOTE: The following numbers are based on 'cold resistance.' Ohms is a measure of resistance and heat affects resistance, so if you test element inside a heated tank, the ohm rating will be different. For example 3500W /240V element can vary from 16Ώ hot to 10Ώ cold. Resource: See chart How to test element Remove wires from element to test. Set multimeter to read ohms Ώ. Each element has volt and watt rating printed on end of element. If element is rated 4500 watts @ 240 volts.... then volts squared (57600) ÷ 4500 watts = 12.8 ohms So 12.8 is the ohm rating for the element, no matter what voltage is applied But what happens when voltage is reduced on the same element?? For example voltage is reduced to 208 volts instead of 240 volts. Then 208 volts squared (208v x 208v = 43264 volts˛) ÷ 12.8 ohms = 3380 watts... and the element does not burn as hot What happens when voltage is reduced to 120 volts on same element? Then 120 volts squared (120v x 120v = 14400 volts˛) ÷ 12.8 ohm = 1125 watts and heating is reduced to 1/4 the original output What happens when voltage is reduced on 480 volt, 4000 watt element? 480 Volts squared (230400) ÷ 4000 watts = 57.6 ohms/ and 57.6 is the ohm rating for element no matter what voltage. So when voltage is reduced to 415 volts: 415 volts squared (172225) ÷ 57.6 ohm = 2990 watts (or 3000 watts as shown in photo) What about increasing voltage instead of lowering voltage? What happens when 480 volts is connected to element that is rated for 4500 watts and 240 volts? POW ! element burns out 480 volts squared (230400) ÷ 12.8 ohms = 18,000 watts or 4 times the rating... and the element will burn out immediately What happens when 240 volts is connected to element that is rated for 2000 watts and 120 volt? POW again 120 Volt squared (14400) ÷ 2000 watts = 7.2 ohm 240 volts squared (43264) ÷ 7.2 ohm element = 6000 watts running through a 2000 watt element causing it to burn out Always buy element that is rated for the voltage Resource: Elements and element replacement |
Both elements in example are rated for 4500 watts @ 240Volt |
Reducing
voltage reduces wattage Resistive loads like water heater elements: watt consumption drops when voltage drops. For example light bulb gets dim in a brown-out when voltage drops across large area of homes. Example formula shows that wattage for 120Volts is 25% of wattage for 240Volts (240 divided by 277 volt)˛ = 75% of rated wattage Save during peak electric pricing by converting water heater to 120V. Not recommended for ordinary usage. Only for peak hours. Connect water heater to generator and have some hot water during power outage. Lower wattage heats more slowly. If elements is rated for 4500 watts @ 240Volt ....and you apply 240volt, you get 4500 watts = raises 47 gallons water by 40 degrees in 1 hour. ....or you apply 120volt, and get 1125 watts = raises 12 gallons water by 40 degrees in 1 hour. Tank stays hot with 120 volt, but amount declines rapidly when hot is used, and reheat is slower. With 120 volt, the electric consumption is spread across more hours. It still takes same amount of energy to heat a gallon water, so cost per heated gallon stays same. Resource: How to convert water heater to 120Volts Connect water heater to generator Recovery chart Figure kWh needed to heat water |
Screw-in elements |
High
and low density elements All calculations shown on this page apply to high and low density elements. Watts ÷ square inches of heating surface = density High density has less square inches of heating surface, so each square inch of element burns hotter. All new water heaters come standard with high watt density elements Low density has more square inches of heating surface, so each square inch burns cooler. If both elements are rated same watts and volts, they will still heat same amount as each other, no matter the density. Purpose
of foldback type low density element: they last longer in
water that has high mineral content, such as hard water. Rule of thumb:
if elements burn out frequently, change to low watt density. Help
prevent burn-out by draining tank periodically and cleaning sediment
build up in water heater.
Resources: How to select and replace water heater element How to test if element is working |
What
does Watt rating mean? Think about the difference between 40 Watt and 100 Watt light bulb. Higher the Watts, the hotter the light bulb, and the higher output of total energy So 5500 Watt element gets hotter than 3500 Watt element, and 5500 Watt uses more total energy Why are elements different Wattage? Think about a light bulb. A closet can be lit with one 40 Watt bulb. But a large room requires more Wattage. So very large water heaters use 5500-6000 Watt element since they heat more water. Most residential tanks have 4500 Watt elements Small 4-20 gallon under-counter water heaters have elements rated for 120 volt and 1500 watt If elements burn out frequently, reduce element wattage, or install low density element. Resource: How to select and replace element | |
Thermostats | |
Thermostats are generic: Substitute Apcom with Therm-o-disc or Apcom or 89T etc Make sure upper thermostat has 3 screws on right side for 2-element tank Temperature range 90-150° Therm-o-disc/ reset trip @ 170° Temperature range 110-160° Apcom/ reset trip @ 180° Local YMCA hot tub = temperature 105°/... Typical shower-bath = 110°F Residential water heater TP valve will release water at 170° Read more about thermostats |
Thermostats work
with any voltage up to 480 volts Thermostats will work with 12-24-36-48 volt AC DC 120-208-240-277-380-415-440 Volt AC up to 480 volt High voltage DC from direct wire to solar panels will melt thermostats. Resources: for
Solar PV water heater:
Convert water heater to high voltage DC Convert water heater to low voltage DC How to set up solar array Thermostats are mechanical bi-metal switches and do not depend on voltage to work. Thermostat must sit flat against tank and be covered with insulation, or they will misread tank temperature. Thermostats temperatures are approximately, and vary by calibration. Residential thermostats are rated 90-160° F/ with reset trip out at 170°F Commercial thermostats are rated 120-180 ° F/ with reset trip out at 200° F Do NOT use commercial thermostats on residential water heater. Cautions: Danger of severe burns with water exceeding 135° F... apply cold water to burns... call for medical help. Electrical burns are different: do not apply water. Elderly people are often not able to feel or respond to hot water ... adjust temperature on water heater to 105-110° F for elderly people... typical hot tub temperature might be 113°F and there is usually a time limit and advisory against folks with breathing problems sitting in hot tub. Do not work on live electricity while wearing oxygen. Oxygen is flammable and can be ignited from electric spark. Make sure power is off. Buy 90-150
degree F for residential tank:
Water heater thermostats at Amazon Rheem thermostats More thermostats 89T short/ dual-element thermostat at Amazon All therm-o-disc products Resources: Select and replace thermostats 120-180° Commercial and 3 phase thermostats How to wire thermostats Add another thermostat to gas or electric water heater Troubleshoot electric water heater Difference between Rheem thermostats |
Calculations | |
Formulas: Volt x Amp = Watt Amp = Watt ÷ Volt More Electrical formulas |
Water
heater label shows Volts and Watts Volts x Amps = Watts --Same as-- Amps = Watts ÷ Volts Calculate amp size of breaker using formula: 5500 Watt element ÷ 240 Volts = 22.91 Amps or 23 Amps Other examples 4500 Watt element ÷ 240 Volts = 18.75 Amps 3500 Watt element ÷ 240 Volts = 14.5 Amps 1500 Watt element ÷ 240 Volts = 6.25 Amps 40 Watt light bulb ÷ 120 Volts = 0.33 Amps If resistive load, such as light bulb or water heater element, receives less voltage, then the watt rating is less. If 40 watt light bulb receives 80 volts instead of 120 volts, then wattage is reduced:: (80 ÷ 120) squared = 44% ... so 40 watt bulb rating is reduced to 40 watt x .44 = 17.6 watts |
Formula for heating water inside
tank: Gallon Per Hour (Electric) = (KW x 3413) divided by (temp. rise x 8.25) or (KW x 414) divided by (temp rise.) Let's say you have one 5500 watt element. Let's say incoming water temperature is 65°F and you want to heat tank to 105°, or 40° rise in temperature. 5500 watt or 5.5Kw elements x 3413 = 18771.5 40 degree temperature rise x 8.25 = 330 So in this specific situation, the 5500 watt element would heat 56.88 gallons per hour If the tank has 2 elements, then the heating load would be shared by both elements. The exact proportion of heating by each element would be unknown. If you have 4500 watt elements and incoming water temperature is 55°, and you want to heat to 120°, then the temperature rise is 65° 4.5 KW x 3413 = 15358.5 65 degree temperature rise x 8.25 = 536 So the elements would heat 28 gallons per hour This number does NOT consider heat loss from tank, where heat is dissipated through tank insulation due to ambient room temperature etc. Remember, with residential non-simultaneous tank, only ONE element is ON at one time. Upper element is ON, or lower element is ON, or BOTH elements are off. At no time are both elements on at same time. |
Wire size and breaker must match Use 10 gauge wire with 30 amp breaker |
Circuit
breaker calculation 10 gauge wire and 30 amp breaker for 4500 watt and 5500 watt elements @ 240Volts safe maximum for breaker is 80% of rated value of breaker ... or to say the same in different way .. breakers should be sized at least 125% of expected heater amperage, per NEC and local codes. 5500 Watt element ÷ 240 Volts = 22.91 Amps or 23 Amps 4500 Watt element ÷ 240 Volts = 18.75 Amps Using oversized breaker and wire will run cooler, and breaker box and breaker will last longer Consider 30 amp breaker: safe maximum is 80% rated valve: or 30 amps x .8 = 24 amps So safe maximum for 30 amp breaker and 10 gauge wire is 24 amps... NOT 30 amps How many watts? 24 amp safe maximum x 240 volts = 5760 watts (amps x volts = watts) |
Wire size and breaker must match Use 12 gauge wire with 20 amp breaker |
Circuit
breaker calculation 12 gauge wire and 20 amp breaker for 3800 watt and 1500 watt elements @ 240Volts 3500 Watt element ÷ 240 Volts = 14.5 Amps 1500 Watt element ÷ 240 Volts = 6.25 Amps Using oversized breaker and wire will run cooler, and breaker box and breaker will last longer Breaker and wire size must match Consider 20 amp breaker: safe maximum is 80% rated valve: or 20 amps x .8 = 16 amps So safe maximum for 20 amp breaker and 12 gauge wire is 16 amps... NOT 20 amps How many watts? 16 amp safe maximum x 240 volts = 3840 watts (amps x volts = watts) If 20 amp breaker is rated for maximum 3840 watts, then it is too small for 4500 watt water heater Replace 4500 watt elements with 3500 watt elements/ heating will be slower, but will get the job done |
Larger image Wire and breaker chart For ordinary residential non-simultaneous water heater Test voltage Identify element wattage Look for total connected watts on label Use chart to find correct wire and breaker Resource: Select correct wire and breaker size |
What
does Watt rating mean? Think about the difference between 40 Watt and 100 Watt light bulb. Higher the Watts, the hotter the light bulb, and the higher output of total energy So 5500 Watt element gets hotter than 3500 Watt element, and 5500 Watt uses more total energy Why are elements different Wattage? Think about a light bulb. A closet can be lit with one 40 Watt bulb. But a large room requires more Wattage. So very large water heaters use 5500-6000 Watt element since they heat more water. Most residential tanks have 4500 Watt elements Small 4-20 gallon under-counter water heaters have elements rated for 120 volt and 1500 watt If elements burn out frequently, reduce element wattage, or install low density element. Resource: How to select and replace element |
Avoid surge | |
Avoid
damage from surge: Most ordinary electric water heaters are NOT damaged by surge. Exception, hybrid heater, Energy Smart or and water heater with electronics. Powerful lightning strike can damage any water heater, especially electronic water heater and other appliances. Simple power outage can also cause power spikes when power is restored Install surge protection at the breaker panel or at the location of equipment Surge protectors are single-use. Over time, all surge protectors wear out because of constant variations in electric power coming over the grid. Resource: Read about Type 1 and Type 2 surge |
Household water heaters are wired for NON-simultaneous operation. Both elements are not ON at same time Resources: How to wire water heater thermostats How water heaters work How to wire off-peak water heater |
Cost and efficiency and meter | ||||||
Residential Electric
heaters have 92% overall efficiency Smaller water heaters (30 gallon) have less surface area and less standby heat loss, and slightly higher efficiency than larger tanks (40-55 gallon). Size chart Residential 80 gallon electric heaters in 2023 must be enrolled in demand response unless you buy heat pump heater or commercial grade 80 gallon heater Read Image |
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Avg electric price by state 2015 Avg state price chart in pdf 2015 How much does it cost to run Electric water heater: 3 hours is approximate daily run-time for a water heater [depending on usage and temperature of incoming water] Bath uses 12-15 Gallons hot water <> shower uses 5-9 Gallons hot water > Hot water use chart 5500 Watts x 3 hours = 16,500 watt-hours or 16.5 kWh per day For a full 30-day month <=> 30 days x 16.5 kWh per day = 495 kWh per month for water heater electricity Calculate cost <=> 495 kWh x $.10 per kWh = $49.50 + tax As general rule, electric water heaters operate at 99% efficiency with or without water-softener > until sediment reaches bottom element > full efficiency is restored when sediment removed How to remove sediment Read research pdf |
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3 hours a day @ $.10 per kWh 5500 Watt tank = 495 kWh per month = $49.50 per month + tax 4500 Watt tank = 405 kWh per month = $40.50 per month 3500 Watt tank = 315 kWh per month = $31.50 per month assuming low usage 1500 Watt tank = 135 kWh per month = $13.50 per month |
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Meter on water heater The kWh meter is din rail mounted inside enclosure. Records billable power usage in kWh. Multiply by rate you pay per kWh to get monthly/ yearly cost of running electric water heater. Buy Bomain power meter Ketotek power meter 240 volt pass through kWh meter 2T2502GA beige plastic enclosure 2T2500GA grey plastic enclosure din rails Resource: Enclosures Figure volts amp watts for water heater | |
100 Watt light bulb turned on for 10 hours <=> 100 Watts x 10 hours = 1000 watt-hours or 1 kWh 40 Watt light bulb turned on for 10 hours <=> 40 Watts x 10 hours = 400 watt-hours or .4 kWh To calculate cost, multiply kWh x price <=> For example .4 kWh x $.10 per kWh = .04 or just 4˘ for each 10 hours of 60 Watt light |
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Small Refrigerator: $60 per year Big refrigerator: $300 per year Small 786 watt Refrigerator rated 6.5 Amp/ full load 115 Volt 1.6 kWh per day = 600 kWh per year. @$.10 per kWh = $60 per year @$.12 per kWh = $72 per year Big Screen TV: $70-140 per year Satellite receiver: $18 per year TV: 300-500 Watts + 3 watt standby $.10 per kWh 6 hours TV per day = $70-140 per year |
Look at appliance label
> each appliance has Watt rating For example double-oven has a Watt rating of 7.0 KW - that means 7000 Watts The top oven uses 1/2 total wattage or 3500 watts or 3.5 KW >> the bottom oven uses 1/2 or 3.5 KW For every hour the top oven is 'on' uses up to 3.5 kWh of power When both top and bottom ovens are 'on' for one hour, the appliance uses up to 7.0 kWh When buying appliance: Look at wattage printed on label. Take photo of label with phone. Compare wattage with old appliance. It requires same energy to heat water and heat homes and cook food as before. A giant appliance does not lower bills. Energy Star rating does NOT mean new appliance will pay for itself. With Energy Star, expect $2-6 per year on same size appliance. Appliances give off warm air that works against AC in summer, but helps heater in winter. Reducing consumption and buying smaller wattage appliance is best way to lower energy bill. Put your TV and satellite box and computer on a power strip/ turn off power strip when not in use Resource: Look at power strips that have timers. Put bath fan, garage light and whole house fan on a countdown timer. Read more about standby power loss Read1 Read2 Remember, when everybody conserves electricity, the price remains low and fewer resources are used Buy: Kill a watt meter Electric testers |
Timers wifi zwave |
Water heater Box timers |
|
Control
water heater with Switches
and Timers wifi zwave The 80% safety rule applies to 15 amp switches and timers, so .80 x 15 Amp = 12 amps maximum So switch and timer have to be wired to a contactor Resources: How to install 15 amp wall timer to control water heater Control water heater with phone Control water heater with switches Ordinary switches can control a water heater |
Buy
from my affiliate links every time/ thanks: Amazon ''As an Amazon Associate I earn from qualifying purchases'' Enter Amazon from any link on my site, fill cart with any item ... purchases pay small commission E-mail: geno03245w@gmail.com My response might end up in spam folder, check email folders Waterheatertimer on Twitter Message thru facebook |