Major heat loss between side arm and fixtures

[SteveoinBoulder]

I am wondering if there is a general rule of thumb with regards to how much heat loss to expect between the outlet from a sidearm (160degrees) and the respective fixtures per foot in a conditioned space (not an exterior wall). With 1/2" copper pipe, I am seeing more than a 50 degree loss at the kitchen sink which is no more than 20' away and a similar amount at some of the other fixtures. The pipes are mostly buried in the floor joists so it's hard to know if they were insulated. Either way, I can't imagine that kind of loss.
Thanks!

 

[Dana]

The outlet of the sidearm should NEVER be 160F if headed for a sink or shower/bathtub- it's dangerously hot! (It's allowed go untempered for laundry or dishwashers.) Codes now require a tempering valve or mixing valve to reduce the temperature of the water going out to showers, tubs & sinks to under 120F. Even if it's not right at the water heater I would expect there is a tempering valve somewhere between the sidearm and kitchen to see that kind of temperature drop.

 

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[Phog]

I agree with Dana, there is no way to get that kind of temperature differential without something mixing cold water in with the hot. It could be a tempering valve, or also a broken recirculation system component (only possible in some certain types of recirculation systems, not in all types). I notice you say "some" but not "all" of the other fixtures in the house have this issue. You should be able to track the pipes of the affected fixtures back to one common branch point, this is where you'll find the component that is the problem. Whatever the broken thing is, it's unlikely (although not impossible) to be buried inside a wall; it's more likely to be in the basement ceiling. Are you sure it's not the whole house being affected? The most common place for a multi-fixture tempering valve is right above the water heater.

 

[Reach4]

The most common place for a multi-fixture tempering valve is right above the water heater.

For economy. The better place would be closer to the point of use, but that would usually take more than one mixing valve.

 

[Plumber Man]

Is the 50 degree drop through the faucet or are you testing it straight out of the shut-off valve at the kitchen sink.
Some kitchen faucets do have a temperature limit stop built-in under the handle.

 

[SteveoinBoulder]

Thank you all for your replies! We ended up drilling some 4" holes in the drywall and finally found a mixing valve! I just love when people bury that under drywall- maybe they never heard of access panels?!? It was set to just over 1 (on a 4 scale). We bumped it to 4 and now have hotter water everywhere. The output at the sink is now 122. Since it's coming out of sidearm at 160- the 38 deg loss must be due to the type of faucet or perhaps the max setting on the mixing valve restricts it somewhat? I am tempted to bypass the mixing valve and drop the temperature of by boiler by 20 deg to save on gas. BTW, I use in floor radiant which requires 130 outflow. Would that be foolish? Anyway, I really appreciate all the help!
Steve

 

[Dana]

Thank you all for your replies! We ended up drilling some 4" holes in the drywall and finally found a mixing valve! I just love when people bury that under drywall- maybe they never heard of access panels?!? It was set to just over 1 (on a 4 scale). We bumped it to 4 and now have hotter water everywhere. The output at the sink is now 122. Since it's coming out of sidearm at 160- the 38 deg loss must be due to the type of faucet or perhaps the max setting on the mixing valve restricts it somewhat? I am tempted to bypass the mixing valve and drop the temperature of by boiler by 20 deg to save on gas. BTW, I use in floor radiant which requires 130 outflow. Would that be foolish? Anyway, I really appreciate all the help!
Steve

Yes, bypassing the tempering valve would be absolutely foolish, quite dangerous, and a code violation. Heating your radiant floor with 130F water isn't foolish, but heating your radiant floor with potable hot water would be (or is?)

Replacing the tempering valve with a thermostatic mixing valve that has more range on the high end would be legal as long as it's still capable of mixing down to 115F. But even 122F/50C is geting into scald hazard territory at a sink.

 

[Phog]

Thank you all for your replies! We ended up drilling some 4" holes in the drywall and finally found a mixing valve! I just love when people bury that under drywall- maybe they never heard of access panels?!? It was set to just over 1 (on a 4 scale). We bumped it to 4 and now have hotter water everywhere. The output at the sink is now 122. Since it's coming out of sidearm at 160- the 38 deg loss must be due to the type of faucet or perhaps the max setting on the mixing valve restricts it somewhat? I am tempted to bypass the mixing valve and drop the temperature of by boiler by 20 deg to save on gas. BTW, I use in floor radiant which requires 130 outflow. Would that be foolish? Anyway, I really appreciate all the help!
Steve

It's definitely the amount of cold water that the tempering valve is mixing in that is causing the temperature drop. I'm wondering if perhaps the valve is old & has started mixing in "too much" cold water. The low #1 setting might have been the correct setting for reducing 160F incoming hot water to 120F back a long time ago. Now that extra cold water is "leaking" through, you've had to turn it up to #4 to get the same 120F. This is especially possible if there have been frequent periods of high flow through the mixing valve over the years -- you can get cavitation under high flow & this can literally eat away at the metal internals over time. You can end up with brass poppets that look like a rat was chewing away at them, just from the water flow, believe it or not.

Anyway my thought is that instead of eliminating that valve, maybe you might want to think about just replacing it with a new one and see where that gets you. (If you're not content with leaving well enough alone.. it sounds like your system is working fine at the moment!)

Also this would be a good time to examine whether the mixing valve's flow rating is appropriate for the system. It might be best to upsize from a 1/2" to 3/4" valve, for example, or even to split up the system and put multiple tempering valves further downstream (each serving a smaller number of fixtures). It's hard to give an exact answer of what the appropriate solution is without knowing the specific details of your home's plumbing system & usage profile, but if you wanted to share those here I'm sure you would get some good advice on what to do.

 

[Phog]

Also, I'm personally a little curious about the floor radiant heat. Does it actually have potable water flowing through it, or is the potable supplying a liquid/liquid heat exchanger for a separate radiant circulation loop?