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I have a regular outdoor spigot fed by a 1/2" copper pipe from the basement through a brick wall. I want to add a hot water feed to it, regulated by a valve to adjust temperature in order to make washing our dog a little bit more comfortable. I'd like to avoid drilling another hole through bricks.

My plan is diagrammed below:

Cold and hot come from the same main feed, with the latter passing through a tank heater.

Is this OK from the engineering point of view to add-mix hot water like this? Should I add check valves?

To put it another way, do bathroom faucets that mix hot and cold water do something more than just combine two flows together that I cannot emulate with a couple of Ts and a valve?

fragment of plumbing diagram

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Rather than trying to tie hot and cold together just add a hot spigot next to your cold spigot and attach a mixer hose like this one

enter image description here

Alternatively you could fit a mechanical mixing valve into the under house plumbing enter image description here

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  • I'd like to avoid drilling through the wall again if possible. – mustaccio Aug 17 '20 at 12:46
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    How do you intend to access the mixing valve under the house? – Kris Aug 17 '20 at 16:46
  • It's in the basement, easily accessible. – mustaccio Aug 17 '20 at 16:53
  • @mustaccio I'd go with the adjustable mixing valve in the basement. The first time or two, it may take some fiddling to get the right temp, but once you've got it set, use a Sharpie™ to mark where to set the valve. After the first bath or two, though, you'll have to corral the dog before setting the valve - even dumb dogs will figure that one out in a hurry... – FreeMan Aug 17 '20 at 17:33
  • Thanks for the idea; I guess I just didn't know what they are called. Most of these come in 3/8" and/or are thermostatic (i.e. don't go to "all cold") but I'll keep looking. – mustaccio Aug 17 '20 at 21:00
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You could put a check valve, or back-flow prevention valve on each supply line before they meet at the Tee. There would be no way to regulate the water temp with that set up.

You could regulate the temp If you added a 1/4 turn valve on each line before the Tee and then partially shut one or both to find the temp you need and then just leave it set that way.

If you were not opposed to putting another hole in the wall, (There is already one there that is fine so why not another), then the proper way to do it is buy a hose bib that is supplied by both hot and cold supply lines and the ability to mix as needed.

Alternatively there are hose bibs designed to have only one hole in the wall. If you went that option then most likely you would have to make your existing hole larger and that can be a real challenge. EDIT: Apparently this product has been discontinued but i would suspect that a person can get one on eBay or find a similar product from another manufacturer.

I found this expensive one.

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  • Here it is on the cheap. Thanks for the ideas. – mustaccio Aug 17 '20 at 20:29
  • @mustaccio Less expensive, NOT cheep. – Alaska Man Aug 17 '20 at 20:39
  • I was being sarcastic. – mustaccio Aug 17 '20 at 20:58

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