Archive for the ‘Hot water’ Category

Hot Water

April 21, 2015

indirect-hot-water

The other day, my son asked about swapping out his current hot water system to an electric hot water tank.

He currently has what is called an indirect hot water heater that uses a zone off his oil fired boiler to make hot water. (See diagram)

There were a number of reasons why he considered doing this.

First, he has electric solar panels on the roof of his house which have lowered his electric costs significantly, so he thought an electric hot water tank might save money.

Second, in the winter, he had issues with his existing system providing enough hot water when he needed it for his morning shower.

Lastly, in the summer, he felt it was not efficient for the boiler to come on and heat up boiler water so it could produce hot domestic water.

electrical-hot-waterHe thought that maybe a stand-alone electric hot water tank (see diagram left) could cost less, provide consistent hot water, and be more efficient.

He asked me what I thought.

Before I tell you what I told him, I want to point out that  there is no simple answer. There are many variables in determining the ‘best’ way to produce hot water.  Variables, like what kinds of fuel are available, what type of budget one has for the initial cost of the equipment, monthly usage cost, and annual maintenance cost.  Also, where he lives enters into fuel costs and availability of expertise in the various solutions.  Other variables are family size and  hot water usage or demands.

Finally, technology and efficiency standards are constantly changing so the answer depends on when he wants to make this change.

To compare heating options, I first need to define a term called BTU’s (British Thermal Unit).  A BTU is a measurement of energy and is defined as the amount of energy to raise one pound of water 1 degree Fahrenheit.  Or for those who are visual, one BTU is equal to burning one kitchen match.

I will limit this analysis to the most common fuel types.  If we look at just cost per BTU, natural gas is the first choice, followed by fuel oil and then propane and electric.

However, fuel costs are seasonal and they vary significantly over time and within the US.fuel-oil-costs

The chart on the above shows that  fuel oil costs for the past two years varied from $2.75 per gallon to over $4.00 per gallon.

 

If we look at propane prices over the past two years (below), we see a big spike to $4.00 per gallon in the winter of 2013-2014 and a leveling of costs in the winter of 2014 – 2015 to around $2.30 per gallon.Propane-costs

 

Natural gas is measured in cubic feet.  Prices fluctuate with demand, so it goes up in the winter time (see below)Natural Gas costCurrently, natural gas prices are very low.  In the last year, prices varied from a low of $9.49 to a high of $17.39 per thousand cubic feet.

Electric costs are measured in kilowatt per hour or kWh.  The costs vary seasonally and throughout the US (see below).  electric cost

The US average is 9.94 cents per kWh.  However, if you live in New England, where my son lives, the cost can vary from 15.94 cents to 20.45 cents, a significant difference.

To compare fuel costs to heat water, we need to determine the BTU’s in a unit of fuel.  Then we also need to take into account two efficiency factors. One is the efficiency of taking the energy in a unit of fuel to BTU’s. And the other is the efficiency to heat water with those BTU’s to the desired hot water temperature.

Below is a chart of the BTU’s in each fuel type and efficiency in converting it to BTU’s. This chart calculates the cost for a million BTU’s using the low and high prices throughout the heating season and various parts of the US.

Unit cost Cost per million BTU’s
BTU’s Units Low  High  Eff. low high
Natural Gas 1,028,000 mcf $9.490 $17.390 82% $11.26 $20.63
Oil #2 138,000 gal $2.900 $3.550 82% $25.63 $31.37
Propane 91,800 gal $2.400 $4.000 82% $31.88 $53.14
Electrical 3,412 Kw $0.098 $0.245 100% $28.84 $71.81

But we still have not made hot water. We only have cost per BTU. Let’s now apply the second efficiency factor to those BTU’s to make water. To get this efficiency, we need to know the input water temperature, the output temperature, the heat loss of the tank, the efficiency of the burners or elements, and heat transfer efficiency.

This can get complex.  However manufactures of hot water systems do provide this data for their equipment. To find it, read the specifications for the system or look for it on a tag that is normally attached.

For my analysis, I’ll simplify it and use the following percentages: fuel oil and gas efficiency hot water tanks are in the 60 – 65% efficiency range; electric hot water tanks are in the 90 – 95% range.

To compare costs for hot water, it really does not matter what we assume for usage, as long as we apply the same usage to the various fuel types. The data is valid for comparison purposes.   I will use 70 gallons of hot water per day for a family of four, input water temperature of 60 degrees, output temperature of 120 degrees which requires 16.3 million BTU’s per year.   The chart below shows the range of low and high annual cost.

Cost  1 million BTUs. Annual cost
BTU’s Units System Efficency low high low high
Natural Gas 1,028,000 mcf 0.62 $18.16 $33.27 $296 $542
Oil #2 138,000 gal 0.62 $41.33 $50.60 $674 $825
Propane 91,800 gal 0.62 $51.42 $85.71 $838 $1,397
Electrical 3,412 Kw 0.92 $31.35 $78.05 $511 $1,272

The bottom line is that for tank type heaters, natural gas is best.  Fuel oil is second best and propane and electric the most costly.

So, what did I tell my son?  Since, he already has a indirect system using his fuel oil fired boiler, the additional cost of getting hot water in the heating season is very small.  So, I told him that replacing his fuel oil indirect hot water tank with a classic electrical hot tank will not be a good idea. His solar power electrical panels may produce electricity cheap, but a hot water tank would exceed the capacity of his panels, causing him to extra kilowatts from his local electric company.

However I should also point out that there are newer technologies on the market.  Tankless hot water, or on demand, systems have been on the market for some time and electric hybrid heat pump hot water tanks are now available.   There are also solar heaters and drain-water heat recover systems.  These systems may offer cost benefits over today’s classic solutions.

There is no simple answer to what is the best way to get hot water.  Below you can find pointers to various websites that I used to answer my son’s question.  You can use them to get an ideal on how to determine the best answer for your own situation.

What is a BTU: www.businessdictionary.com/ and wikipedia.org

How much water average homes uses: http://www.oeic.us

Average electrical cost – www.eia.gov

Selecting a new hot water heater: energy.gov

To calculate cost of fuel to generate BTU’s: http://nepacrossroads.com/fuel-comparison-calculator.php

Average hot water usage and cost per year:  ugi.com

 

 

This blog was written by Fred Wilbur. Fred was an employee of Keith Specialty Store from 2005 – 2015 and today enjoys sharing information to help people have a better life.

Submersible pumps – 2 or 3 wire?

June 1, 2011

Submersible Water Pumps, 2 or 3 Wire.  What is the Difference?

 Submersible pumps, the kind of pump that goes in your well or cistern, are available with two wire motors or three wire motors.  There is also another ground wire which is not counted, so if you look at the pump the actual number of wires will be three or four.  The two wire pump will have two black wires and one green ground wire.  The three wire pump has a black, red, yellow and green wire.

You are probably thinking, “That’s nice, but what is the difference to me?”  The main difference is the three wire pump uses a separate control box which includes a capacitor and relay to start the pump.  The control box is located inside your house or pump house.   The two wire pump does not use a control box.  Everything is built inside the motor of the pump.  All motors larger than 1 ½ HP are only available in the three wire version because you need the control box to start the heavier motors.  Most residential pumps are smaller horsepower.  Our top selling pump is just ½ HP.

Many years ago we sold mostly three wire pumps.  We believed that having a separate control box above the well would sometimes save people the time and expense of pulling the pump when they experience a problem.  If the problem is in the control box it is a simple and relatively inexpensive fix to replace the box, as opposed to pulling the pump and replacing the motor or whole pump.  This is the main advantage of the three wire pump.  Then, probably 25 years ago, a local plumbing contractor insisted he had far fewer problems with two wire pump systems.  We slowly shifted to selling more two wire pumps and our experience seemed to agree with the contractor’s observations.  Also, two wire pumps are less expensive, the wire used to install them is less expensive and the installation is easier because you do not have to wire through the control box.  Of the pumps we now sell, at least 90% of them are two wire.

Which size wire and breaker do I need for an electric water heater?

May 31, 2011

Which size wire and breaker do I need for an electric water heater? 

The wire and breaker size depend on which heating elements are in your water heater.  Find the watt rating  for the elements.  This rating is usually on a tag on the side of the water heater.  It is also printed on the elements.  You can find the elements on the side of the heater under a plate attached with one or two screws.

For elements up to and including 2500 watts, the minimum wire size would be 12 gauge.  With 12 gauge wire, use a 20 amp breaker or fuse.  For elements over 2500 watts you must use 10 gauge wire and a 30 amp breaker or fuse.   It is important to match the wire size to the correct breaker or fuse.  The breaker protects the wire from overheating.  You can use 10 gauge wire for lower wattage water heaters.  If you are running wire for a new water heater, it is a good idea to use 10 gauge so that you are covered for any water heater you might buy in the future.

You can find wire on our web site at: http://keithspecialty.com/elec.cable_wire.htm

Electric Hot Water Heater – Elements

May 14, 2011

How Do I Determine Which Element I Need for My Electric Water Heater?

 If you run out of hot water faster than you used to, have only lukewarm water or no hot water at all, it is possible that one of the elements needs to be replaced. How to accurately diagnose a faulty element is a topic of another post.  This post assumes you have already determined that you need new elements.  It discusses how to determine which element you need and how to replace them.

There are two types of elements found in the majority of water heaters:   a flanged element or a screw-in threaded element.  There are some other types on older heaters, but they are becoming very rare.

Flanged hot water element Flanged Element 

Screw in hot water element Screw-in Element           

Hot Water Element socket wrench Socket Wrench

                                                                    

Always turn off the power supply to the water heater and drain the water from the tank before working with the elements.  Most water heaters have two elements while some have only one.  The elements are located on the side of the tank behind a metal plate attached with one or two screws.  Remove the plate.  There will be two wires attached to the element.  Loosen the screws and remove the wires.  Don’t worry about remembering which wire went to each screw, it doesn’t matter.  It will now be obvious which element you have.  If you see four bolts, it is a flanged element.  Remove the bolts and pull the element straight out.  If you have a screw-in element, you will see a single large hex head on the element.  A 1 ½” deep socket can be used to remove the element or you can purchase an element socket wrench.

The wattage and voltage will be printed on the head of the element.  Some elements will have two different listings such as 3500W at 208V and 4500W at 240V.  Use the larger number when ordering.  You may want to replace both elements while you have the tank drained, even if only one is bad now.

Important reminder!  After installing the new element, always refill the tank with water before turning the power back on.  Open a faucet while you fill the tank to be sure there are no air pockets remaining inside the water heater.  Since elements are made to be submersed in water, they will burn out in seconds if you turn on the power to the tank before it fills completely.

 

Other informational sources:

  •  A diagram of hot water tanks – from HowStuffWorks.com
  • Good video on replacing an element.  Note: this video does not discuss filling the tank with water before turning on the elements.
  • Another source of how to change an element from Ehow.com

I just had city water installed and now my water heater leaks out of my relief valve!

April 25, 2011

You just had city water installed, and now your hot water tank is leaking out of the relief valve!  The following information will provide steps to help you solve the problem.

The first rule to remember is that as water is heated, it will expand.  Before getting city water you likely had a pump and cold water expansion tank in your house.  As the water heater did its job, the expanded water would push back the line into the expansion tank.

It is common after installing city water to have no expansion tank and a check valve installed in the new waterline.  When the hot water tank heats water, the expanded water has nowhere to go, thus building excess pressure and blowing it out of your water heater relief valve.

Expansion tank

Wilkins Expansion tank – item 41-300

The solution is to install a small expansion tank on the cold water line above your water heater.

We carry an expansion tank for hot water. It is our item # 41-300, a Zurn XT-8.  A tee fitting is required for the cold water line to go to a ¾ “ female pipe thread to accept the tank threads.  You will need enough room for the tank to hang.  It is advisable to have some support for the water line as well,  to avoid putting undo strain on it, causing it to break and create another problem.

relief valve

Relief valve

You may also want to replace the relief valve, our item 41-274, on your water heater as it may still drip after being opened by high pressure a few times.

Good article on expansion tanks from a code point of view: http://www.wvdhhr.org/phs/water/thermal_expansion2.pdf

Here is a link to Zurn’s installation document. for the XT expansion tank.