Cold water rushing past heating element. Will the element feel hot?

In summary, the hot tub will not heat up until the water has reached a certain temperature, and the amperage of the heater is not very high.
  • #1
bobbo7410
36
0
Curious question, figured what better place to ask than the physics forum.

So I just picked up a used hot tub. Was running great when I bought it. Filled it up with water, turned it on, started its cycle. It can take over 24 hours for the tub to reach 102 degrees.

There's a 12 inch heating tube in which water rushes past, "heating" the water which gets pumped back into the tub. Now I when I touch the heating tube, it doesn't feel hot to the touch. Though perhaps it won't feel warm/hot until the water equalizes in temp? Perhaps a strong flow of freezing water would essentially cool the heating element just as much as it would be heating it up, so I wouldn't immediately feel the tube get hot?

Anyone have any thoughts on this? (or perhaps it should get piping hot immediately and my heater is busted) I'm thinking I should feel some sort of heat...
 
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  • #2
Do you know how much heat the heating element is supposed to dissipate? Can you measure the amperage of the element or hot tub?

Yes, it is possible for the pipe to still be cool to the touch just downstream of a heating element, depending on the particular geometry.
 
  • #3
russ_watters said:
Do you know how much heat the heating element is supposed to dissipate? Can you measure the amperage of the element or hot tub?

Yes, it is possible for the pipe to still be cool to the touch just downstream of a heating element, depending on the particular geometry.

I'm not sure how much heat it's supposed to dissipate nor can I readily measure the amperage. I know it is a 1kw heater...

Here is the actual diagram. The section labeled 1 represents the 12" long heating tube, that is the heating element itself. Water rushes through it. That tube is cold to the touch. The water currently rushing through it is approx 50 degrees or less.

[PLAIN]http://img440.imageshack.us/img440/6126/asdfsdaf.png [Broken]
 
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  • #4
I've had a couple of hot tubs.

The outflow won't be that much warmer than the inflow. No, it should not feel hot to the touch, not until the water's temp is higher.

Stick a thermometer in the tub. It should be rising a degree or two an hour. (You don't need to wait hours & hours. How long has the tub been running? How cold was the initial water? At ~2 degrees her hour, is it already several degrees warmer?)
 
  • #5
What you want to be worried about with a used tub is leaks.
 
  • #6
DaveC426913 said:
I've had a couple of hot tubs.

The outflow won't be that much warmer than the inflow. No, it should not feel hot to the touch, not until the water's temp is higher.

Stick a thermometer in the tub. It should be rising a degree or two an hour. (You don't need to wait hours & hours. How long has the tub been running? How cold was the initial water? At ~2 degrees her hour, is it already several degrees warmer?)

Thanks dave! Yeah I popped a thermometer in it when I first turned it on. The initial water temp was 51 degrees. It is now showing 53ish degrees and has been exactly 1 hour. The outside temp is 33 degrees. There are quite a few variables that could influence only a few degrees of change, yet nonetheless it looks promising.

I think I was initially concerned because I figured I would most definitely would feel some heat from the heating element. Though had to step back and think from the other end of the spectrum, such as flushing cold water to cool a hot element.
 
  • #7
bobbo7410 said:
I'm not sure how much heat it's supposed to dissipate nor can I readily measure the amperage. I know it is a 1kw heater...
1kW is the heat it is supposed to dissipate.

That's not a lot of heat - enough to heat a 1m radius by 1m deep tub 0.87C per hour. Is it cold and dry where you are? Can you cover the hot tub? What's the volume of the tub?
 
  • #8
russ_watters said:
1kW is the heat it is supposed to dissipate.

That's not a lot of heat - enough to heat a 1m radius by 1m deep tub 0.87C per hour. Is it cold and dry where you are? Can you cover the hot tub? What's the volume of the tub?
It will surely come with a lid. Not much use without one.
They are typically 200-500gal corresponding to 2-6 person tubs.

[EDIT] Yep. The pump diagram is for a TX which, according to Solana's website (http://www.solanaspas.com/ [Broken]) is a 130gal 2-person tub.

As for cold and dry, well, he says it's 33 degrees. (Presumably, that's F).


This is just like my situation. And yes, it takes just about 24 hours to come up to temp.
 
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  • #9
Chicago IL here, constant 33 deg F. The tub is indeed 130gal with a nice insulated top. It's been rising steadily every hour. 51-53-55-56-59

Thanks for all the helpful info!
 

1. Will the water temperature affect the heating element?

Yes, the water temperature will affect the heating element. As the cold water rushes past the heating element, it will absorb some of the heat and cause the element to feel hotter.

2. Can the heating element overheat due to the cold water rushing past it?

It is possible for the heating element to overheat if the cold water is rushing past it at a high velocity. This can cause the element to reach higher temperatures than it is designed for, potentially causing damage.

3. How does the flow rate of the cold water affect the heating element?

The flow rate of the cold water can affect the heating element in several ways. A higher flow rate means more water passing by the element, which can cause it to feel hotter and potentially overheat. Additionally, a higher flow rate can also lead to faster heat transfer, which can impact the overall efficiency of the heating element.

4. Will the heating element feel hot even if the cold water is being continuously replenished?

Yes, the heating element will still feel hot even if the cold water is being continuously replenished. The temperature of the water may be lower than if it were stagnant, but the constant flow will still cause the element to heat up.

5. How long will it take for the heating element to cool down after the cold water stops flowing?

The time it takes for the heating element to cool down after the cold water stops flowing will depend on various factors such as the initial temperature of the element, the duration and intensity of the cold water flow, and the surrounding temperature. In general, it will take a few minutes for the element to cool down completely.

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