Water heater - how hot is too hot?

[kenmac]

I also wonder about the high temperature cutoff in the regulator itself. I can't find any documentation of what mine is set for. It's a Robertshaw propane regulator, and have read that these don't self reset once they trip. So, I want to avoid activating that safety device by having the water in the tank too hot.






That high limit you are talking about is a small wire that's under the thermocouple. It runs inside the thermostat bulb in the tank. I have had some to reset & some won't .You would have to try to relight the pilot to see if it will relight ( after the water cools down) to know if it will reset or not. It should cut out some where around 180-190 deg.(this would be higher on some commerical tanks) water temp. It only shuts the gas burner off to the W.H. Most people don't do it .But, the maker of the T& P valves state that the valve should be manually operated about every 3-6 months to make sure it is functioning properly (not sticking) I wouldn't want to go over 180-190 deg.tank temp. Some T&P valves will began to open at around 200-205 deg. even though it's rating states 210 deg.If the control knob is turned to HOT. The water temp should be 160 deg per robertshaw. Perssure & temp is something you would want to keep to within or under the safety devices limits

 

[charlz]

I'll be using a tempering valve to keep the water going to the faucets at a safe temperature. That doesn't concern me. The effect of the higher temperature on the water heater itself is what I'd like to know.

What about using a tempering valve between the wood furnace loop and the water heater? I am not familar with these but I saw this:

Watts Series 70AT Hot Water Extender Tempering Valve 3/4" (0215480) - PlumberSurplus.com

Perhaps these is a way to rig this so it puts hot water into your water heater when water is drawn? Won't exactly do away with your hot water heater needing to run to maintain temperature but certainly would eliminate recovery time etc.

Charles

 

[adlertom]

That high limit you are talking about is a small wire that's under the thermocouple.

It should cut out some where around 180-190 deg.

I wouldn't want to go over 180-190 deg.tank temp. Some T&P valves will began to open at around 200-205 deg. even though it's rating states 210 deg.

If the control knob is turned to HOT. The water temp should be 160 deg per robertshaw.

THANK YOU KENMAC! These are the types of numbers I was seeking.

If 160 F is the max temp with the control knob turned all the way up, I would think that it'd be OK for me to heat the water to that temp with my wood system. I'll be conservative and use that as my maximum water temperature, even though the safety devices may allow for a somewhat higher temp before activating.

 

[adlertom]

What about using a tempering valve between the wood furnace loop and the water heater?Charles

I understand what you are saying, but that would be more problematic. Since all of the water in the wood furnace loop is hot, there is nothing cooler to temper it with.

I also thought of regulating the flow of wood burner loop water to the heat exchanger with some sort of mechanical thermostatic valve, that closes more tightly as temperature rises. I couldn't find anything on line like that though. I could do it with an electric valve and aquastat, but that would involve more parts and complexity.

Does anyone know of such a temperature valve that operates mechanically?

 

[charlz]

I understand what you are saying, but that would be more problematic. Since all of the water in the wood furnace loop is hot, there is nothing cooler to temper it with.

What I was thinking is you would put that valve in front of your hot water heater on the cold inlet. You would have hot coming from the wood furnace heat exchanger and cold from the well/city service. (Putting your heat exchanger in front of the water heater not looping through it). This way the tempering valve would have cold available to it. Instead of heating the water in the tank you are putting hot water into the tank on the cold inlet as hot water is drawn. This way you are not overheating the tank and the tank only needs to maintain temperature when water is not being drawn.

I guess the factor here is how fast your heat exchanger can heat incoming water. If it was fast enough you could do away with the tank all together and go 'tankless'. Likely that will not happen and you will be putting 'warm' water into the tank requiring the water heater to warm it up the rest of the way. Not as cost effective as a thermosiphon loop constantly heating the water but does address the max temp issue.


Here is another thought.

At Costco they sell a device which is designed to provide 'instant hot water' at the facets. Basically what I think it does is 1)you put in some type of check valve between your hot and cold lines at the sink 2)at a preset time (right before you wake up) it adds pressure (via pump) to the hot water lines, the valves open and hot water flows to the sink and back into the hot water heater via the cold water pipes. When you turn the facet on to shave or whatever the water is already hot, thus saving you water by not waiting for it to get hot. In my mind this wastes energy but whatever. You could use something like this that would periodically come on and heat up the water in the tank. Or just a valve that would periodically open and let the thermosiphon loop do its trick. With some experimentation you could come up with timing that works pretty well. By setting the hot water heater itself to the lower/lowest setting you would be saving quite a bit as it only comes on for 'emergency' type heating (ran out of hot water).

Just some thoughts.

Charles

 

[Racer71]

Aldertom,

What you need is a valve to shut off the water loop from the stove. This valve would trigger on the temperature inside the water tank.

Any plumbing store should be able to help you. I have hot water heat with 5 zones. Each zone has its own valve and thermostat. The hot water is one of the zones.

 

[kenmac]

THANK YOU KENMAC! These are the types of numbers I was seeking.

If 160 F is the max temp with the control knob turned all the way up, I would think that it'd be OK for me to heat the water to that temp with my wood system. I'll be conservative and use that as my maximum water temperature, even though the safety devices may allow for a somewhat higher temp before activating.

Glad to be able to help.


You never want to use a safety device as an operating control. These sould only be used / activated in an emergency situation.
Also check your T&P valve from time to time to make sure it isn't sticking. You may want to purchase & have a new T&P on hand as, sometime when you open them sediment can become trapped under the rubber seal & keep them from sealing back off. It your T&P is several years old . I would just replace it & check the new one every 3-6 months to make sure it isn't sticking

 

[Bill Barrett]

To keep it simple, you could use a mechanical thermostatic valve on your heat exchanger. Thermostatic Diverter or Mixing Valve this will give you the idea. I know this is a three way, you could use to bypass your heat exchanger, two way are avallable. Or go with a injection system,http://www.blueridgecompany.com/documents/Taco_RMB-1.pdf

 

[RonMar]

How exactly is your flow configured? Is the boiler circuit pumped thru the heatex below the water tank, with the domestic water from the heatex thermosiponing thru the water heater tank?

 

[adlertom]

Aldertom,

What you need is a valve to shut off the water loop from the stove. This valve would trigger on the temperature inside the water tank.

Any plumbing store should be able to help you. I have hot water heat with 5 zones. Each zone has its own valve and thermostat. The hot water is one of the zones.

Yes, that would be one solution. It would require an electric valve and thermostat, and a supply of power.

I would prefer a simpler, mechanical only solution if available - some type of temperature controlled valve that closes when the water flowing through it reaches X degrees, and reopens when it cools.