Recently installed a new water heater. Installation manual was pretty specific about the need for an expansion tank, claiming they were a code requirement these days.
House is ~20 years old, and does not appear to have an expansion tank. In fact, I’d never seen or heard of one until I saw them when I was browsing Home Depot’s website looking for a water heater.
I understand the concept - expansion tank allows for thermal expansion of water in pipes, since backflow preventer will not allow water to flow back from the house to the city - but are they really necessary? My house’s plumbing has apparently survived 20 years without one. Given the construction date, was it perhaps built before backflow preventers were in use?
We had an older house with a relatively new water heater. Then the city installed a water meter (part of a long-term shift in consumer billing) and it included an anti-backflow valve.
Problems started almost immediately from the backpressure of heating water. I am trying to remember exactly what - might have been the pressure valve blowing, might have been some kind of leak. The pressure build up was substantial. I put a gauge on an outside faucet and from the end of a 5-minute shower, pressure would build from around 45 psi nominal to over 60 in a matter of minutes.
Anyway, I had to install a pressure-relief tank to cure the problem. That pressure cycling is not good for household fixtures and piping, and if there’s not even slight pressure release back into the incoming system, sumpin’s gonna blow.
(Damn… I wish I could remember what the exact problem was. It was… significant.)
I don’t know when they started making them code, but I don’t remember expansion tanks being necessary around here 20 years ago.
As I understand it, it’s a question of whether your water pressure is high enough and whether or not you have a backflow preventer installed. If your water pressure is low enough then you can probably get by without one, though I think most water heater manufacturers demand one now. I suspect that they are making the water tanks out of thinner metal and the pressure and water hammering that you can get if your water supply has a backflow preventer could cause the water tank to weaken and rupture over time due to metal fatigue. So even in areas where it’s not code you often have to install the expansion tank just because the heater manufacturer will void the warranty on it if you don’t.
Poking around on google, it seems that the backflow preventers come from a 2005 addition to the Safe Water Drinking Act. While the act doesn’t require backflow preventers, the other requirements of the SWDA may make it difficult for your city’s water supply to pass the SWDA without them.
So yeah, within the last ten years seems to be roughly the right general time frame. I can’t remember when it was, but probably somewhere shortly after 2005 is when our local water company installed new meters. Like Amateur Barbarian’s case, ours also came with new backflow preventers installed, and also included a pressure regulator of some sort (some little gizmo attached to the pipe, not an expansion tank).
If I understand correctly, the regulator only regulates the pressure that can be developed by the water source (the city) in your home’s piping; it doesn’t stop thermal expansion (in conjunction with the backflow preventer) from generating even larger pressures.
When your water supplier installed these new meters, did they suggest that that would be a good time for you to put an expansion tank in?
Although our house was built 20 years ago, we only bought it about 8 years ago. The city (Ann Arbor, MI) has since updated the meters to allow for remote/electronic reading, but I don’t know whether there’s a backflow preventer there or not. I suppose a pressure gauge (throughout the duration of a water heater cycle) would be a good thing for me to try out.
Water does not compress worth a damn. That is why underground pipelines are pressure tested with water even if they are going to carry a gas like ‘natural gas.’
Fill with line with water and leave a very small airspace. pump until the line explodes or you get to a pressure passing pressure. Very small crater because the pressure bleeds off very fast compared to 5 miles of 24" line pressured to 2000 pounds…
Old houses, the tanks had blow off valves or overflow valves as some called them. Tank get too hot or pressure got too high, it opens up and relieves pressure until it comes down to a safe level. Also if you had a washing machine connected, the rubber lines would expand and help keep the pressure down.
The strength of the lines, black iron, copper, and now plastic also has a lot to do with how much expansion pressure you need to deal with. Add in back flow prevention and some kind of pressure release is needed if the lines and normal water valves, like the toilet, kitchen sink, etc. are not strong enough to hold that pressure.
Today things are not as often overbuilt as was the norm in the past. So you end up needing to spend money to save the cheaply made components of today. The end user is the one who gets to pay this bill.
I wonder what the cost difference is between the savings of the cheaper faucets vs the pressure relief system that is code approved?