water heater question

[farquad]

i've done a search here on this site for this problem and haven't found an answer to the question so i decided to make a post. btw, great site that has made it to my bookmarks and i had absolutely no problem registering with to post.

my wife and i purchased our first real house a little over a year ago. the home is about seven or so years old now. during our purchasing process i insisted on having a home inspector go over the home from top to bottom and me being on site with the inspector when he was performing the inspection because of the large investment at stake and me lacking knowledge of home construction. the guy seemed very thorough and pointed several things out. one of the things he had pointed out was the water heater had been what he said, "relieving itself" into it's drain pan. i asked him how serious this was and his reply was that if it continues to have someone qualified come out and check the unit out and adjust it if necessary because it's either building up too much pressure or running too hot. being a now disabled aircraft mechanic this made sense to me and i've been monitoring the unit since but haven't noticed anything except till recently. the unit sits in an non-climate controlled garage, on the floor (of course), in a black drain pan that has a pvc outlet on it where i guess some sort of tubing could be attached if necessary.

now maybe this behavior is normal and my concern is all for nothing but i'm looking to learn about it and want to know if it is normal or not. to make an attempt to stop this on my own i had pulled the cover plates off the unit last night and found two thermostats at both the top and bottom of the the unit. they were set @ just below 120 degrees F (approx one needles width), but not evenly. the bottom one was slightly higher than the top. not seeing a need for this high of a temperature and not seeing any valves in line on top of the unit in the hot line, i dropped the temperature to about 105/110 F on both thermostats and re-installed the covers. i dried out the drain pan and this morning noted no water in it. maybe this worked??? or do i have another problem??? the reason i went ahead and did what i did was to maybe get a jump on things and it seemed to have made sense to me.

here are some details on my unit i can provide. if anymore info is needed (or even pictures), please let me know and i will get needed info asap!

whirlpool water heater
us/craftmaster water heater company
58 gallon capacity
model# E1F50RD045V
date: 8/2003

environment:
3 bedroom, 2 bath home. have washer and dishwasher. 2 adults and 2 kids ages 10 and 1 1/2. we use a lot of hot water!

thanks for any help (if i need any) you can provide. again great site!

[LazyPup]

Good Morning Farquad,

Great question and very well written, providing plenty of diagnostic information to help resolve your problem, but then being an aircraft mechanic I am sure you have made a career of being attentive to detail.

The overflow valve on a water heater is a Temperature & Pressure Relief Valve, properly abbreviated as a TPRV but commonly referred to as a T&P (temperture and pressure valve).

The purpose of the valve is to relieve either the pressure or temperature well below the conditions necessary to cause a water heater to explode therefore the T&P valves are designed to release if the temperature in the tank exceeds 210degF or if the pressure exceeds 150psi.

You stated in your post that the thermostats were set at slightly below 120degF. The plumbing code states that the maximum allowable temperature in the water distribution system is 140degF and all showers must be equipped with anti-scald valves whenever the hot water temperature exceeds 120degF. In order to insure we stay within those limits it is customary to set the water heater for a maximum of 120degF. You have not mentioned any of the conditions that would be indicative of erratic temperature so for the moment let us rule out temperature as the cause of your problem. FYI- I would suggest that you do return the thermostats to 120degF because there is some concern that certain bacteria can thrive in a water heater at temperatures under 115degF.

The second condition that can cause a T&P valve to relieve is pressures in excess of 150psi however the plumbing codes limit the operational pressure of water distribution systems to a maximum of 85psi and in instances when the supply pressure exceeds the maximum we are required to install a PRV (Pressure Reducing Valve) on the the main line near the main water shutoff valve. If you have a home well the operating pressures are typically set to cut in (start the pump) at 40psi and cut out (stop the pump) at 60psi which is well below the maximum rating. Here again, there is no mention of the other conditions that would normally be associated with high pressure so for the moment I am going to rule out pressure as well.

Understanding that the T&P is a temperature & pressure relief valve and by now having ruled out both temperature and pressure the question becomes "What ofther conditions could cause the valve to relieve?"

Most compounds found in nature expand when heated and contract when cooled however water has a very unusual characteristic. Water reaches maximum density at 39degF and will expand in volume if either heated above or cooled below that temperature.

By code water lines must be buried a minimum of 6" below the average frost depth for any given locality. In summer the soil temperarute is generally very close to the earths natural geothermal surface temperature of 55degF or wamer from sun radiation, but in winter as the frost enters the ground the surface soil freezes and the temperature slightly below frost depth will be at or very close to the 39degF maximum density of water. This means that as your water passes through underground piping it will be entering your house at or near its maximum density and when heated in the water heater expansion begins.

Water, like all liquids, is not compressible therefore as the water expands the increased volume must go somewhere. In the case of a frozen water line the increased volume is demonstrated by rupturing the pipe wall. The amount of force generated by water expansion is tremedious when we consider that freezing can rupture copper or iron pipes and even cast iron radiators or engine blocks in our automobiles which explains why we must put antifreeze in the car. The actual amount of expansion is in the order of +10% by volume when water is either heated or cooled.

Under normal circumstances as the water expands the increased volume is either absorbed by the air chamber in the pressure tank of our home well pump system or in the case of a municipal water supply the excess volume backflows out the water supply line to the municipal main, however, if our system happens to have backflow preventer (check valve) on the municipal main supply line or on our home well pump downstream of the pressure tank the remaining supply lines and water distribution lines are now a closed system with no provision for expansion. In this case the increased volume is relieved by occassional discharges from the water heater T&P valve.

There is no real problem here aside from the inconvience of the occassional water discharge but a permanent solution can be had by installing an expansion tank on the cold water line directly above the water heater.

[farquad]

LazyPup,

I appreciate your reply and i won't quote it because of it's length.

as for pressure in my system...now that i think of it...when i first turn on any faucet in the house there is somewhat of a burst and than it does back down to a normal flow. all of my faucets, except a tub, are the handle type and what i'm talking about when i turn them on it could be full cold, warm or hot. it doesn't matter. there's a rush at first until it slows down to what i would say is normal. now there is an adjustable valve on the main which is a Watts Regulator, N35B, Model-DU, Set STD 50, Range 25-75, Size 3/4. my guess is that this regulates the pressure coming in from the city water supply like you mentioned.

thanks for the tip btw on the bacteria @ lower temps. we'll get that back up tomorrow. yuk!


i understand the comments on the density of water and the pipes needing to be at a certain depth. i also understand how the density changes as well as volume.

something i left out in my first post was that my wife had noticed that it was difficult to adjust the temperature of the water in the shower. just a hair in one direction and you'd either freeze or be burning. i'm used to fine tuning things so it never bothered me. this morning, since i turned the temperature down, i noticed it to be better and i asked my wife about it and she said it was perfect.

now for lack of tools and knowledge of home plumbing...would it be absurd to take a meat thermometer and open up the hot water on the faucet closest tot he hot water heater and get a temperature reading of the water coming out? i know i'll lose a degree or two because of it traveling through pipes but i'm wondering about this now. or am i just be overly concerned and the thermostats are really acurate with where you set them at?

thanks for the help and reply!

[LazyPup]

Creating finitely accurate thermostats is a costly undertaking. For that reason in order to keep the cost of water heaters down typically the thermostates used on water heaters are in a range of about +/- 4 or 5 degF from the actual set point however they are very consistant at maintaining a specific set point. What this means is that while the actual temperature of the water may vary 4 or 5 degF from the actual number indexed on the face of the thermostat the water will remain very constant at the actual temperature the water heater produces at a given set point.

It is a common practice to allow a water heater to run for about 24 hours to stabilize the temperature, then conduct an actual field test in the manner you describe by measuring the output temperature at a nearby faucett then tweaking the thermostat a bit if desired.