Hot water supply- change from 3/4 to 1/2?


Old 06-30-08, 08:36 PM
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Hot water supply- change from 3/4 to 1/2?

We have hot water supplied from a coil in our boiler and it has to travel 50 or so feet through 3/4 copper to reach taps.
The outside supply line is plastic with a shallow well pump set at 30/50 and a pressure increaser that ups peak pressure to 90.

My elderly father complains about the time it takes to get hot water across the home to the sinks or tub.

He wants to change the 3/4 copper to 1/2 and is convinced that will make the hot water come faster.

I can see that there will be less water in the pipe to displace with hot as it runs, but it seems like the pressure in back of the line will be unchanged and I am worried that this will result in less hot water at the tap mixing with higher pressure cold.

Is his idea to change to 1/2 inch hot supply going to solve our problem or make it worse?
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Old 06-30-08, 08:49 PM
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With 1/2 pipe, the water will reach the taps quicker as there's significantly less 'cold' water stored in the pipes. The problem is if two fixtures are used simultaneously, you won't have enough water pressure to supply both evenly, and you'll get stuck with a drop in hot water (temperature) in your shower.

Some people resolve this issue by using 1/2 "home runs" where each fixture has it's own 1/2" run to the source (water heater), so each fixture has a dedicated amount of water.

Another solution you should look at is a circulating pump. There are a few different styles, but basically when the hot water temperature at the farthest faucet cools, it pumps hot water either back to the water heater or into the cold faucet, ensuring that you always have hot water available. Some people swear by them, and others feel that it's a waste of energy based on having to heat the water constantly.

If it's not already, you can also consider insulating the hot water pipes to keep the stored water warmer for longer.

Good luck!
Old 06-30-08, 08:57 PM
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The hot water supply line was insulated when the new furnace was installed 4 years ago.

I thought we might have to reduce the size of the cold lines as well- at least for part of the distance.

I suppose we could also adjust the mixer valve on the furnace to supply hotter water, but that would potentially create a burn hazard when running the tap to the hot side.
Old 07-01-08, 03:32 PM
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So, referencing another post elsewhere,

50ft of 1/2" diameter pipe = 0.51 gallons
50ft of 3/4" diameter pipe = 1.15 gallons

Basically, that's the amount of potable but cold water that must be run to get hot water down a 50ft pipe. A little more, perhaps, once you count in the need to heat the pipe itself. I could see this being an irritation for the sink, but would imagine it's not more than 20 seconds of running the water in the tub to get hot.

The three options I see would be to either add a recirculating hot water pump, with the aforementioned issues and the cost, replace the copper pipe to cut the amount of water/time approximately in half but at the risk of introducing new problems (not to mention the expense of the pipe, fittings, and time to install), or install a small (1-2.5 gallon) point-of-use water heater inline just before the sink.

Of the three, I would imagine the third is the least expensive fix. Downside is that it doesn't reduce the amount of time to wait for the tub water to warm up. Upside is, that's not really a huge deal (as the tub faucet gpm is likely much higher than the sink's and therefore less of a wait) and your dad should just get over it.
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