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temperature relief valve/ demand type water heater


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I found a drain line coming off of a temperature relief valve on a tankless unit today which ran uphill. I know this would be a problem with a conventional tank with a temp and pressure relief valve, and I can't for the life of me see why it wouldn't be a problem with a tankless unit also. But before I wrote it up I wanted to get some mo' input. What say y'all?

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Same requirements as far as I know. The manufacturers installation instructions are for the valve, not the heater and are almost identical to the code requirements if I am not mistaken. A trapped line can still be blocked by freezing water and the valve can still be fouled by water sitting against the face.

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I've seen some uphill retrofits around here lately, particularly in crawl spaces, with a tiny hole drilled in the bottom of the low point and the state plumbing inspector has approved of this.

Just FYI.

That used to be allowed around here too. It's a dumb idea. If the point of running the pipe uphill is to prevent water damage in the basement, then the hole negates that entire idea. Water shoots out of the hole when the valve is open and after the valve is closed, all of the water in the pipe runs onto the basement floor anyway. What's the point of going uphill again?

The little hole in the uphill pipe was *never* allowed by the manufacturers.

If you'd like to put your water heater below grade, then you should figure out an acceptable location to run the TPR discharge.

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I've seen some uphill retrofits around here lately, particularly in crawl spaces, with a tiny hole drilled in the bottom of the low point and the state plumbing inspector has approved of this.

Just FYI.

That used to be allowed around here too. It's a dumb idea. If the point of running the pipe uphill is to prevent water damage in the basement, then the hole negates that entire idea. Water shoots out of the hole when the valve is open and after the valve is closed, all of the water in the pipe runs onto the basement floor anyway. What's the point of going uphill again?

The little hole in the uphill pipe was *never* allowed by the manufacturers.

If you'd like to put your water heater below grade, then you should figure out an acceptable location to run the TPR discharge.

I haven't seen the little hole but yes, that's funny.

Put a pan under it and a water alarm in the pan.

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Well, I will show my ignorance here...

First, why does a "tankless" water heater need a TPR? There is no tank to overheat, rupture and create a missile. What am I missing?

I ask because we have one installed in our barn in the mountains of NC. There are no provisions on the unit for a TPR and I questioned both the plumber and plumbing inspector and both stated a TPR was not needed.

For your reading pleasure, HERE is a link to the manual for the unit.

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Well, I will show my ignorance here...

First, why does a "tankless" water heater need a TPR? There is no tank to overheat, rupture and create a missile. What am I missing?

I ask because we have one installed in our barn in the mountains of NC. There are no provisions on the unit for a TPR and I questioned both the plumber and plumbing inspector and both stated a TPR was not needed.

For your reading pleasure, HERE is a link to the manual for the unit.

If the burner, for any reason, should fail to shut down when the call for heat is ended, it could end up boiling water in the heat exchanger tubes and pressurized the entire hot water circuit in the house if if wasn't for the TPR valve.

Marc

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Well, I will show my ignorance here...

First, why does a "tankless" water heater need a TPR? There is no tank to overheat, rupture and create a missile. What am I missing?

I ask because we have one installed in our barn in the mountains of NC. There are no provisions on the unit for a TPR and I questioned both the plumber and plumbing inspector and both stated a TPR was not needed.

For your reading pleasure, HERE is a link to the manual for the unit.

Required in Massachusetts. Page 4, second paragraph from the bottom. What does MA know that the rest of the country doesn't?

If you're on the IRC for plumbing, it sez, "P2803.1 Relief valves required. Appliances and equipment used for heating water or storing hot water shall be protected by:

1. A separate pressure-relief valve and a separate temperature-relief valve; or

2. A combination pressure- and temperature-relief valve.

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