# How does it take a lot of skill to be a good plumber?

jbriggs444
Homework Helper
2019 Award
I just don't see how the heat pump (heating 55F water with 60F ambient) can be more efficient than direct heating (whether it's a resistance heater or a gas flame).
Heating 55 degree water with 60 degree ambient could theoretically generate energy. The efficiency gets so good it's actually negative :-). But that only works to get the water up to 60 degrees.

Unless you are being very clever with your heat exchanger(*), the thermodynamic efficiency depends on the ratio of the absolute temperature of the hot water divided by the absolute ambient temperature. If your target temperature is 150 degrees, that's ##\frac{150+459}{60+459}## which gives a ratio of 1.17. If I remember the math right, that means that 0.17 units of electrical power plus 1 unit of ambient thermal energy gives you 1.17 units of thermal energy in the hot water. That's an "efficiency" of 688%, ideally. Real world will be worse, of course.

Compare that to resistance heating with an efficiency of 100%.

In an apples to apples comparison, I think gas burners come in at around 250% -- you're not dealing with a 40% efficient natural gas powered generator and transmission system.

(*) By getting clever with the heat exchanger, I am imagining a kind of Rube Goldberg arrangement where you raise the water temperature from 55 to 60 and gain a tiny bit of energy back. Then you raise the water temperature from 60 to 65 with an outrageously high efficiency (about ten thousand percent). Then you raise it from 65 to 70 with a bit lower efficiency (about five thousand percent) and so on. You get an efficiency of 688% for the last five degrees.

Last edited:
russ_watters
thanks @jbriggs444 -- I need to work through this. For me it's academic since I have moved but I'd like to understand it.

russ_watters
Mentor
I just don't see how the heat pump (heating 55F water with 60F ambient) can be more efficient than direct heating (whether it's a resistance heater or a gas flame).
In mixed-units it isn't readily apparent, but even a normal air conditioning unit is much, much greater than 100% "efficiency". Federal standards in the US requires a minimum of 380% (13 SEER) for residential split systems. But they call it "Coefficient of Performance" or "Energy Efficiency Ratio" to avoid accusations of perpetual motion.
Heating 55 degree water with 60 degree ambient could theoretically generate energy. The efficiency gets so good it's actually negative :-). But that only works to get the water up to 60 degrees.
I'm not sure that's true. Since as you pointed out you can actually generate energy with a negative delta-T, you can get whatever output delta-T you want for free, as long as the working fluid flow rate is larger on the sink side than on the source side. E.G., for a basic home air conditioning unit both the input and output temperatures for the condensing unit are much higher than the indoor temperatures, yet the efficiency ratio is still 380%+. Why? Because the airflow (mass flow rate) across the condensing unit is much larger than on the indoor/evaporator unit. For a negative delta-T on the sink side, you can power anything and generate anything you want.

 --- ehh, actually, you may need to discard much of the water in order to do that.

Last edited:
jbriggs444
Homework Helper
2019 Award
@russ_waters responds to claims of "negative efficiency".
I'm not sure that's true.
It is kind of true. If you take the ratio of the heat you see added to the water to the electrical energy you put into the system under thermodynamically ideal reversible conditions, you get a negative result -- you put negative energy in and get [60 degree] "hot" water out.

Calling that ratio "efficiency" is certainly a stretch. But it is not nonsensical.

Negative efficiency (in this sense) is better than positive efficiency in a similar manner to how negative temperatures are hotter than the hottest positive temperatures.

Last edited:
russ_watters
Mentor
@russ_waters responds to claims of "negative efficiency".

It is kind of true. If you take the ratio of the heat you add to the water to the electrical energy you put into the system under thermodynamically ideal reversible conditions, you get a negative result -- you put negative energy in and get [60 degree] "hot" water out.

Calling that ratio "efficiency" is certainly a stretch. But it is not nonsensical.
Sorry, I re-arranged the post several times, but didn't really get my point across: the part I'm not sure is true is that you are limited to 60 degrees output temperature. I think you actually said this in your own postscript:
By getting clever with the heat exchanger, I am imagining a kind of Rube Goldberg arrangement where you raise the water temperature from 55 to 60 and gain a tiny bit of energy back. Then you raise the water temperature from 60 to 65 with an outrageously high efficiency (about ten thousand percent). Then you raise it from 65 to 70 with a bit lower efficiency (about five thousand percent) and so on. You get an efficiency of 688% for the last five degrees.
This sort of arrangement probably requires discarding some water, but you can get whatever output temperature you want, for free, when you have a negative delta-T.

jbriggs444
jbriggs444
Homework Helper
2019 Award
This sort of arrangement probably requires discarding some water, but you can get whatever output temperature you want, for free, when you have a negative delta-T.
Ahhh, I had not envisioned going down that road -- running your hot water heater on a Stirling engine harvesting the massive thermodynamic energy in the 5 degree temperature difference. :-)

I was an electrician apprentice for three years, and you get respect for your fellow tradesfolk very quickly, or else you end up causing stupid conflicts that just slow up the job.

Imagine walking into a 10,000 square-foot "room", bare concrete floor and ceiling, exterior concrete walls in some areas fronted by heavy-gauge metal studs. You have a thick roll of papers in your hand; on one page per trade, the overall end-result is drawn in detail. You have to look up at that concrete ceiling and envision where every single major item is going to travel, in three dimensional space

In a best-planned job, fire-suppression comes first. Plumbers trained in fire-suppression carry 80-pound blackpipes into place and route them overhead for every room--rooms that, remember, don't even exist yet--then run smaller pipe out to every location a sprinkler needs to be set. Everything is graded correctly so water flows down at the right speed and volume if ever the heat-sensor pops.

The joints have to be perfect--absolutely perfect, so that for 80 years, the network of blackpipe running above the ceilings, out of sight, rarely if ever maintained or even looked at, will remain leak-proof; not one location will ever rust inside or out to a degree that would result in a leak or a blockage; and the system will perform perfectly any time it may be called upon.

It's geometry; physics; hydraulics; chemistry. It's precision of layout, advanced planning, and knowledge of all the associated materials for mounting to the ceiling, and that mounting, too, must hold up 80 pounds of pipe FULL OF WATER for every 10 feet of travel, without falling out of the ceiling for the next 80 years.

Failure has deadly consequences. And that's just the fire-suppression system.

Then there's the potable water for drinking, washing, lab sinks, toilets; and the drains that carry that water and also wastes away. If you screw up, toilets clog, or sewer-gas rises not directly up out to the roof vent but instead into the cleaning closet's floor drain.

Connections are made available for things such as refrigeration units and water-baths for lab work, and of course run through hot water heaters; some of which, in a commercial setting, engage directly with the HVAC system. These things have to be put in side-by-side with the electricians and HVAC workers, again starting before there are even walls to tell you where those sinks and toilets will end up (though of course, at ground-level you're also working beside carpenters who build the walls, and you coordinate with them to place everything in precisely the right location--theoretically.) The blueprints very quickly devolve into general ideas of how to get it done, but on the ground, you have to work with all the details that no architect or engineer realizes exist.

A plumber, an electrician, over the course of their careers they'll probably never meet two identical situations for any given job, even though they're all similar; and every single job has some stupid quirk to deal with. A cabinet comes in from a manufacturer two months after the drains were set into the concrete floor, and the internal construction of that cabinet sits directly on top of the drainpipe. Or you've got to compensate for the loss of water-pressure as you work your way up a 30-storey building. Or the required drop in slope for a potable water line runs you smack into conflict with the work of another tradesperson who got there first, and you're at the end of the line and have very little space in which to work out the problem.

There's everything in the trades, which is why I loved it so much. Manual labor and mental labor, every day. Precision and skill, pride in walking away knowing that any other tradesperson coming to make a change in 10 years will pop up a ceiling tile, look at your work, and think "Thank goodness," because it's not a sloppy mess they'll have to fight against. Constant changes as technology improves. Again, that interplay of chemistry, physics, engineering, and 3-dimensional visualization that's the biggest LEGO set you've ever dreamed of. You get to know thousands of parts and dozens of iterations for each one, like knowing all the different types of LEGO brick and non-brick. Invent new ways to solve non-standard problems, at least once on every job, usually at least a couple times a month.

Then there's the law involved. As an electrician, if I screwed up, people might die, property might be burned to the ground. So our legal document was over 700 pages long, and we had to know large sections of it in every detail; and the entire thing had to be so familiar that if we didn't know the regulation and requirement off the top of our head, we could locate it quickly--even if it was a once-in-a-lifetime installation. Did you know that you have to put a grounding grid beneath a cattle milking floor, lest a short electrocute every cow who steps onto it, and perhaps the farmer as well? I've never even been in a milking barn.

If a plumber screws up, they're unlikely to kill anyone, so that's good. Except that their pipes and my conduit, should the two meet, had damned well better be protected against galvanic screw-ups that rust one pipe or the other, and a leak that gets into my system could cause serious hazards, from shorts in my electrical system, to a flow of current through their pipe and the water inside.

A building with plumbing only, the only hazard would be flooding or sewage interactions; but plumbing interacts with everything else, even natural gas, so the legal document a plumber must memorize has got to be about as hefty and intense as ours was.

And that's just commercial work. Get into the great big industrial work, you're into another apprenticeship, a whole different field; get into residential work, and you're dealing with an unending parade of other-people's-screw-ups. That's a science in and of itself, a problem-solving job more than a construction job. Try renovating a 100 year-old farmhouse that's been plumbed by six different people in 6 different decades, and how many of them had any training at all?

Tradespeople don't always do very well in the jobs or schools where "genius" is given its definition. But their genius can be very bright indeed--that's what I learned before I got hurt and had to leave a trade I loved. Their genius is not expressed through a page but through a pipe-wrench; not through their mouth but through their hands. It IS genius, true genius. Imagine walking into a 10,000 square-foot room with 30-foot ceilings, looking up at a bare concrete surface, and envisioning every single pipe for sanitation, potable, fire-suppression, natural-gas; going to every room, every appliance and sink; interacting with every other piece of equipment from every other trade? Can you create that sort of picture in your mind, from a single flat piece of paper? I knew tradesmen who could. It was awe-inspiring.

If only they hadn't been such a bunch of sexist, racist bastards ... not all of them, but enough to make life hell. Not true everywhere, I guess; and thankfully, the younger generation not only don't buy into that, some of them actually stand up to it.

I'd recommend trades to any intelligent, strong, young person who enjoys making things. It's financially worth it, and very mentally rewarding as well.

Tom.G, BillTre, jrmichler and 2 others
FactChecker
Gold Member
"How does it take a lot of skill?" -- Believe me, there is a trick to everything.

I have been trained as an HVAC technician before, and I have worked as a residential HVAC technician, but I quit HVAC to go back into trucking because I could not bear to work in the hot attics (140+ degrees fahrenheit) in the summertime. I have heard that soon truck drivers will become obsolete and robots will be driving semi-trucks. When human truck drivers become obsolete, I will need to switch careers. I have been considering many different careers I could go into. My father recently told me that he had an epiphany. He said that I could attend a plumbing program at a trade school, and since I would then have had training in both HVAC and plumbing, I could be useful to large apartment complexes as a maintenance man.

I asked my father if plumbing is a highly skilled occupation, and he said that plumbing is a highly skilled occupation. I have never worked as a plumber, so I might be unaware of some sort of important facts that make plumbing a highly skilled occupation. But I don't see how plumbing would require a lot of skill & knowledge. In HVAC, one must learn all about electricity and how electric motors work, so I can see how HVAC is highly skilled. In plumbing, you don't even use electricity at all, except with water heaters. I see plumbing as just consisting of using an augur to clear out clogs in pipes and installing faucets mostly. I don't see how that would require an enormous amount of skill.

If you agree with my father that it takes a lot of skill to be a good plumber, what is it about plumbing that requires a lot of skill and training to be a good plumber?

-------------------------------------------------------------------------------------------------------

Edited to add: I am just asking how it takes a lot of skill to be a good plumber out of curiosity. I don't deny that it takes a lot of skill to be a good plumber. Since I have never worked as a plumber, I am just asking this question to learn why it takes a lot of skill to be a good plumber.
LOL I bet you I can find a Nuclear Physicist who went to Harvard who can not use any type of wrench

KWolf12