How do I get more shower pressure?

by David Thielen   Last Updated January 12, 2018 22:21 PM

We just moved from our old house which had great shower pressure to our new house which is pretty pathetic. I'm trying to figure out what/where the problem is.

The old house was built about 40 years ago and has plumbing fixtures from about 15 years ago. The showerhead is about 25 years old and is awesome (named Country Club). This house has 2 - 55 gallon hot water heaters (I have 3 daughters).

The new house is brand new so all plumbing & fixtures are new. This house has a Rinnai tankless hot water heater.

At both houses I set the pressure regulator at the max. At both houses using a RainBird pressure gauge I get 80psi on the ground floor faucet at the old house and 81psi at the new house. On the second floor shower I get 76psi at the old house and 75psi at the new house. So that appears equivalent.

The problem appears to be two things.

First, with the shower head off, the old house shower delivers 5gal/min (hot) while the new house it's 2.86gal/min (warm) & 2.67gal/min (hot). The warm/hot is setting the Rinnai to 106/140 and setting the valve to the middle/mostly hot.

And at the new house the ground floor outside faucet only delivers 3.43gal/min.

Why such a difference in water delivered? The pressure is the same. In both cases nothing else was using water at the time. And the fixtures all use 1/2" lines so even if it's 3/4" up to the fixture, it's 1/2" from there. So shouldn't both be delivering the same volume?

Second problem. At the old house I would put the valve pretty much even between hot & cold to shower. At the new house, with the Rinnai set to 140, I still have it about 90% of the way to full hot.

So what is my main problem? I think the first problem is getting 5gal/min. As the outdoor faucet doesn't hit that I don't think the hot water heater is a part of that problem. But what/why/how do we not get that when the pressure is the same?

And then do I need a hot water heater that can deliver 5 gal/min at 140 to have the shower be half hot/half cold to get the full pressure?

thanks - dave

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