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Old house has lots of 3/8 water line feeding faucets. I want to replace the shutoffs under the sink but really hard to find 3/8 sweat valves. I don't want to use compression on the copper line. Can I use a reducer fitting to increase to 1/2 line then use a 1/2 sweat valve? Dont want to run all new 1/2 line up there.

  • Hello, and welcome to Home Improvement. Interesting question; let's see if our pros have a good answer. And, you should probably take our tour so you'll know you'll know the details of contributing here. – Daniel Griscom Mar 7 at 12:34
  • Please clarify so your issue is crystal clear: is the house supply pipe standard 1/2" copper (5/8" O.D.), with 3/8 tube from the stop-valves to the fixtures? Note: it would be very unusual to find the house supply 3/8", which is what one of the answers below addresses. – Jimmy Fix-it Mar 7 at 16:06
  • 3/8 to half are less common because most homes are plumbed with 1/2” . Yes you could sweat an adapter to use 1/2” valve it won’t take measurably longer to get warm water because you are only making a short size change. The one thing I would verify is pipe or tubing. Pipe and tubing are different sizes 1/2” pipe is measured by the inside diameter. 1/2” tubing is measured by the outside diameter. I mention this because the 1 time I found 3/8 plumbing it was tubing , I also do hvac so it was no problem as I had the needed adapters but be aware they are different. – Ed Beal Mar 7 at 16:09
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Not too hard to find the product that you need without having to resort to adapter fittings. See picture source link.

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Picture Source

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  • Agreed , make sure to pull the valve stem while sweating , and verify tubing vs pipe if the fitting doesn’t fit. – Ed Beal Mar 7 at 16:11
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Yes, that's a bit of extra plumbing work but you can upsize from 3/8" to 1/2" with a transition fitting and use 1/2" valves.

I'm not clear why you can't find 3/8" sweat valves though. Any plumbing shop should have them as they are common.

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  • Thanks, thought so. Unable to find on internet either even special order. 1/2 are common and less expensive it just looks weird to upsize. – C Ro999 Mar 7 at 13:17
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Edit. Sorry, misread the question. One issue you might notice is that your hot water may take longer to come out of the tap. This would be more noticeable on long runs.

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