3/4in water supply lines to water heater on 1/2 in main line

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Brodanik

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I'm a do it yourselfer, so be kind lol. I have 1/2in pipe all through my house including my main water supply line. We already have poor water pressure which is the reason for this question. I'm going to replace the hot water heater but it seems like I can't find a corrugated steel 1/2in supply flex hose, unless it's from random online sites, which I don't trust. I decided on corrugated steel because it seems to last longer from everything I've read. I ordered shark bite 1/2in push connect to 3/4in water heater hose, but was under the impression that the hose itself was 1/2 in, not just the connector. It turns out the hose is actually 3/4in. I'm sick of shopping around and I wanted these hoses for durability and convenience. Will my water pressure be heavily effected by using 18in 3/4in supply lines in a house with 1/2in water lines? I would be using 2, one on cold side, one on hot side, totaling 36in. I know I could straight pipe it with 1/2in like it is now, but I was looking to do an easier diy job. Thanks in advance for any advice on the situation.
 

wwhitney

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Will my water pressure be heavily effected by using 18in 3/4in supply lines in a house with 1/2in water lines?
No.

If everything is 1/2" and you have poor flow then as you do work on the water lines, it's worth selectively(*) upsizing them to 3/4" or 1". When you have two sizes in series, it's not the case that the smallest one acts as a throttle and so the larger portion is useless. Rather, it's just that each foot of 1/2" pipe has more drag than each foot of 3/4" pipe, and the more of the system that is the smaller size, the more the total drag at the outlet. [Where drag means pressure loss during flow.]

Cheers, Wayne

(*) Don't upsize a hot water line just serving a single fixture, or serving 2 sinks, or a sink and a shower. That would just increase your wait time for hot water without helping flow much.
 

Brodanik

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No.

Cheers, Wayne
Thank you so much for your response. I just needed some reassurance. I appreciate the detailed response. In addition to the 1/2in pipe throughout the house, every one on our street has bad water pressure, but the water company claims it's acceptable. If I had great water pressure to start, I wouldn't worry about a small loss in pressure, but I can't afford to lose what little I have.
 
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