Installing a Water Heater - what about the water pressure?

October 2, 2006 2:36 PM

What does the water pressure coming into your house have to do with installing a water heater?

I live in a 20 year old house with 2 water heaters: one in the basement and one in the attic. The attic water heater started raining water into the bathroom below yesterday so we decided it was probably time to get a new one. Now the guy installing it tells me that in addition to the $299 installation fee, I also need to install flexible piping ($60) and that the water pressure coming into my house is too high and that they need to install a new water pressure valve for $199. I think they're ripping me off - I can understand the need for the new piping because the current water heater is connected with rigid copper piping, but I already bought an expansion kit to go with the water heater that I thought controlled the water pressure coming into the water heater. So do I really need to change the water pressure for the whole house? Not to mention the fact that I've always thought this house had terrible water pressure and I'm not too keen on bringing it down further. So can anyone tell me if this is something that really needs to be done?

posted by katyjack to Home & Garden (12 answers total)

Speculation: a water heater has to have a pressure relief valve; otherwise there's an explosion hazard. If the water pressure coming into the house is high enough, water would leak out of the pressure relief valve constantly. Thus it would be necessary to reduce it at least going into the water heater to prevent that.
posted by Steven C. Den Beste at 3:25 PM on October 2, 2006

If your main PRV wears out, which they tend to do after twenty years, the pressure relief valve on the top of the water heater may release hot water to prevent the whole tank from rupturing. This water should be diverted to a drain so it doesn't flood your house, but it's not an indication that you need a new tank. But tanks only last about 20 years, so you might need a new one anyway. Why don't you get the plumber to put a pressure gauge on various taps in the house to demonstrate the need for a new PRV?
posted by weapons-grade pandemonium at 3:26 PM on October 2, 2006

I just bought a 1" pressure reducing valve for a big plumbing project I'm doing (one that includes a new water heater, too). I'm DIYing it, but the valve was about $60 retail. You probably have a smaller PRV (maybe 3/4") which should be even cheaper. I think $200 is pretty high, particularly when they're already charging you $300 for installing the new heater.

Get another quote, unless you've already bought the new heater. In which case, get another quote for the installation.
posted by spacewrench at 3:31 PM on October 2, 2006

If your main PRV wears out, which they tend to do after twenty years, the pressure relief valve on the top of the water heater may release hot water to prevent the whole tank from rupturing.

Exactly. Where's the water coming from Katyjack?

Our TPV (water temperature pressure) valve went last week on our 10 year old heater. Water spewing from the relief pipe on the side of the unit. It was an $8 fix including plumbers tape and plumbers putty and took maybe 45 minutes total because we had a hard time getting the old valve off the machine. (Channel locks did it, btw.) I found a lot of info here.
posted by jerseygirl at 4:13 PM on October 2, 2006

If your water heater didn't have a pressure relief valve, or it was stuck shut, and the thermostat failed, it could turn itself into a bomb. I used to have a small collection of stories to that effect. Some of them knocked down substantial portions of houses, as I recall.

It's interesting it happened in your attic heater; water pressure was lower to that heater than the other one because of its higher elevation, so probably the heater did have a a problem.

However, you might find it interesting to poll your neighbors, particularly any whose houses are downhill from yours, to see if anyone else had a similar problem in the same time frame. Once, my relief valve blew the same night the cold water feed backed out of its fitting under the kitchen sink, which just happened to be a day and a half or so after some near-record rainfall in the municipal water supply watershed. When I found out two of my neighbors had also had relief valve failures, I was pretty sure the city had fallen asleep at the switch and allowed water pressure to go way over specs, but they wouldn't talk to me about it, and I decided not to pursue it.

I do think, though, that lots of municipalities are careless about keeping water pressure from spiking, so I would probably go for the whole-house water pressure valve.
posted by jamjam at 6:37 PM on October 2, 2006

IMHO, the installation quote should include plumbing to the new heater if the install is in the same location as the old one. At least that was the case when Lowes did mine a couple of months ago for 259 or so. So the extra charge for "flexible piping" raises a flag for me.

I don't know anything about PRVs. My installer never said anything and I don't even know if my house has one. From what others have said and having a general idea of how much plumbing stuff tends to cost, the quote sounds like a lot.

So I think there's a good chance this guy's trying to milk you, but I'm a homeowner, not a plumber -- can you call a neighbor for another opinion? Water heaters go all the time so odds are somebody nearby's gone through the same process recently. Maybe they can even offer a referral to a plumber they trust for a second opinion.
posted by Opposite George at 7:19 PM on October 2, 2006

The main PRV is adjustable. Loosen the locking nut on the top, then turn the bolt (clockwise usually increases the pressure). If it's full counterclockwise and the pressure's still too high in the house, then you need a new PRV.
posted by weapons-grade pandemonium at 7:27 PM on October 2, 2006

Oh and another thing -- even if code doesn't require it, install a pan with drain to the outside under the new attic heater, so the next time your heater fails it doesn't drip water all over the floors below.

On second thought -- is it possible the flexible piping is FOR a pan/drain the installer's adding? Pans are cheap ($10-15) but I don't know how big a pain it is to run a new drain so that might be it.
posted by Opposite George at 7:31 PM on October 2, 2006

The water pressure valve he wants to install is sort of the water equivalent of a surge suppressor for electricity. It guarantees that the water pressure in the house doesn't exceed a certain level, no matter what is trying to come in. If the plumber thinks your water heater blew because of a transient spike in water pressure, which isn't far fetched, that may be why he wants to install one. (Or replace the existing one.)

But I suggest you get another estimate from someone else, just to be sure he's not trying to rip you off.

Those kinds of pressure valves are pretty cool, but if the water in your area has a lot of minerals in it, eventually the moving parts stop moving and then it's just a pipe.
posted by Steven C. Den Beste at 8:25 PM on October 2, 2006

Here are a couple of stories of exploding water heaters.

The spectacular first one happened a few miles from where I lived, and got me interested in the topic in the first place.
posted by jamjam at 8:25 PM on October 2, 2006

Everything you always wanted to know about PRVs*

*Okay, maybe not everything, but at least it explains what it does and why houses on city water have one.
posted by Opposite George at 12:30 AM on October 3, 2006

You are right to have your BS detector going off. You'll need to learn a bit about what code in your area requires and what should be done in your situation. The way you describe things, you don't really know yet.
posted by kc0dxh at 7:15 AM on October 3, 2006