Monitor hot water tank temperature

[gregyyc]

After having the outside intake pipe get covered in snow and shutting down my gas hot water tank this morning I'm looking for a way to monitor the temperature of the water in the tank to alert the Elk M1 if it drops below a certain level.

I thought of using a temp prob on the pipes but that wouldn't work since overnight no water would flow causing false reading.

Anyone ever overcome this problem?

Thanks!

 

[wuench]

Maybe attach the sensor to the outside of the tank near the bottom. It should read relative to the temp inside the tank.

 

[Desert_AIP]

The temperature in the tank is stratified, hot on top and cool on bottom.

First you need to decide where you want to monitor.
Is the top third enough hot water?
Second third?

You should be able to put either a thermistor or a temperature sensitive snap switch under the insulation against the wall of the steel tank at the proper point.

 

[gregyyc]

The tank is sitting right on the ground so there is no way to mount anything underneath it (at least not without disconnecting everything).

I've looked all over the outside and access panels with an infrared thermometer and haven't found anything much beyond room temp (which is good I guess considering I'd just be losing heat).

Not knowing much about hot water tank construction is it difficult to get a temp probe under the insulation? The plan was to use this : http://www.smarthome.com/1283ZTR/M1-Zone-Temp-Interface-7-Foot-Probe-M1ZTSR/p.aspx but maybe there is an easier option.

 

[apostolakisl]

I would think you could attach a temp sensor to the outlet pipe right where it comes out of the tank and get a reasonable idea if the tank has shut off.

For a more accurate number you can put a tiny little re-circ pump between the hot water outlet and cold water inlet. If the pump just moved a few ounces of fluid a minute you would get a pretty accurate temp by reading the pipe temp where it exits the tank.

For more accuracy, they make temp probes that are part of a pipe fitting such that the temp probe is directly in the water. Combined with a re-circ pump you should see the exact temp of the water.

 

[Jwbarrett]

You could try this - take a metal L bracket and attach a 120 dregree rate of rise sensor to.
Use a magnet to stick to the top of the hot water tank (assuming it metal ) adjust the hight of the sensor so its next to the flue pipe about 1/8 inch away.
Every time the hot water tank fires the flue should heat up and trip the sensor. Then you just need to figure max time for the tank not to run and how long it runs when water is not not being used but just heating up the water, like at night. Then Write a set of rules for it. I did this to track when my oil buner runs

 

[znelbok]

I have looked at the same thing, no to detect if it is off, but to be able to torun the tank on and off. We have a solar hot water tank and through summer you dont need the power/gas on to heat it up that extra bit, so at the moment we turn it off manually. get a couple days of rain and if you have forgotten to turn it back on you end up with a luke warm shower.

I am planning on using this
http://www.temperature.com.au/download.aspx?name=SD%20012tx%20Ex%20ia.pdf

The "hockey puk" gives me a 4-20mA output that goes into the M1.

The probe is inserted into the top of the tank at the outlet. normally the outlet pipe comes out and then turns, but with a small modification, an extra tee the temp probe will insert into the outlet of the tank and not significantly block the flow of the water.

Temperature is merasured at the end of the probe. you can order these as long as you like so you can get into the middle of the tank if you wish.

Some tanks also have a second outlet (and inlet) on them (left hand and right hand). you could just stick thin into the spare outlet that would normally be blocked off.

You dont get to select at what height you want to measure your tank temperature with this method, but it should do the job that you need it to do.

Mick

 

[picta]

I use this sensor on my water heater out pipe

http://www.gsistore.com/jocotetese22.html

There are only a few degrees difference between the pipe temp and the temp sensor that is built into the heater, so you can "calibrate" the reading or you can just note what reading corresponds to a fully heated tank. In addition we have a relay that simply disconnects a wire of external mechanical thermostat when we want to turn the heater off. When disconnected, the thermostat will not call for heat, and it operates normally once re-connected. That design is less intrusive as it avoids interfering with the water heater mechanics and does not require high voltage relays. We also have a few more of these sensors attached to recirculation water line to turn the pump off when the hot water reaches the fixture that is calling for hot water.