Gas pipe reduction question

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Old 12-14-09, 02:36 PM
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Gas pipe reduction question

I'm installing a tankless water heater, and the connection for the gas line is a 3/4" T. However, it is stepped down to 1/2 inch on the side of the T that is accessible, so my plan is to install a 1/2" to 3/4" reducer, which will restrict the size of the pipe to 1/2" for about 3", but it will then open back up to 3/4". Basically I will have a length of 3/4" followed by a couple inches of 1/2" and then another length of 3/4". I realize this will reduce the flow of gas some, but will it effect the flow rate as much as having a full run of 1/2" pipe would?
 
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Old 12-14-09, 03:16 PM
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Yes.

Instantaneous (tankless) gas water heaters use a huge amount of gas. If you are trying to replace a tank-type water heater you may (usually) need to replace piping all the way back to the gas meter. Do you have any other gas appliances that are served by the 3/4 inch piping?
 
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Old 12-14-09, 06:42 PM
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The 1.5" service line comes in, T's off to a 1" line that heads to the furnace and a 3/4" line that then T's off to a 1/2" dryer line and a 3/4" line that T's off to a 3/4" line for the stove and a 1/2" line for the current water heater. My plan was to take the old water heater line and increase it to 3/4", but there would be the 1/2" bottleneck that I mentioned before. There is a union on a 3/4" piece before the T to the dryer and stove/heater that I could break and insert a 3/4" T for the new tankless so that I would only have to replace the dryer line and hook back up to the line running to the stove. That way I can run 3/4" line all the way to the new tankless heater.

Thanks for the help. Let me know if you are able to decipher the situation above and see any problems.
 
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Old 12-15-09, 01:57 AM
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Well, you sound like you are capable of making the calculations to engineer the gas piping system so here is the simplest link I know of on the subject. It is for connecting a generator to a natural gas system but the principle is the same. Be sure to do the complete calculation to be sure all appliances have the proper sized piping.
natural gas piping system
 
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Old 12-15-09, 10:36 PM
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I think that you're saying that a 3/4" feeds both the water heater and the stove. Tankless water heaters are an efficient way to make hot water, but they need a LOT of gas right now. Some residential gas meters are too small to handle the load.

Anytime that I've seen problems with tankless water heaters, it's been 90% undersized gas, 9.8% some other installation problem, and 0.2% something wrong with the unit itself.
 
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