Heat pump water heaters

[jlv]

Using an expansion tank to take all excess pressure off the water heater's tank seems to work well to increase longevity of steel/glass tanks. It does have to be properly adjusted to work right.

I wonder if that's our problem. The 50 gal natural gas hot water tank in our house tends to last 8 years. We've gotten 2 replaced by the 10 year warranty (just paying labor to install a new one). We have very high water pressure.

We've liked the natural gas hot water heater because it has always worked when we had a power outage (a hot shower in the cold dark bathroom is acceptable). We've been here 30 years and have 3-4 outages a year. Because of where we are hooked to the grid, we tend to be more affected by outages and ours last longer as our service is often the last to get repaired.

But now that we have battery backup in the house (2x PowerWalls) along with the PV on the roof, I'm thinking the next time I need to replace the HW tank I'll go with not powered by natural gas (still have to convince the Mrs. of that).

 

[goldbrick]

I just replaced both the pressure regulating valve and the expansion tank in my house. After some interweb research, I found that expansions tank seem to last < 10 years on average. I always thought of myself as pretty knowledgeable about the various systems in my house but I never thought about expansion tank maintenance.

Here's what I learned in a nut shell:

Get a $10 water pressure gauge from your local hardware or big box store. Put it on a hose bib where you want to measure the water pressure. (mine was 100 PSI due to the broken pressure regulator valve). Assuming the water pressure is where you want it, check the expansion tank. It should have a shrader valve on it and you can check the air pressure there. When you open the valve, if water comes out, that means the membrane inside the tank is broken and the tank needs to be replaced. Go back to your local hardware or big box store and buy a new expansion tank. Inflate the tank so the air pressure matches the water pressure you measured before. Install it and that's it.

This all started for me since the water valves on my washing machine had failed. One thing led to another as they say and I think it's all fixed now but I was a bit surprised that I had never heard that these things need to be checked regularly and maintained before causing other problems.

 

[LeftieBiker]

Expansion tanks used to be good for 20 years or more, but I'm not surprised that that has changed.

I wonder if that's our problem.

Sounds like it. We used to get at most ten years from a tank, and they always failed by cracking. Our water pressure runs 100psi or more.

 

[GerryAZ]

If your house is hooked directly to a municipal water system without a pressure reducing valve, then an expansion tank will not help because the pressure at the hot water tank will be the system pressure. As the water is heated, it expands but the system pressure remains the same because the water expands back into the system. If you have a check valve (such as discharge line from a well pump) or a pressure reducing valve in the supply line, then an expansion tank will help to avoid overpressure as the water heats when there are no faucets open. My experience is that I get 6 to 10 years before a glass lined steel tank begins to leak. Since my off-peak power is relatively inexpensive, I would not save enough in 6 years to make up for the higher initial cost of a heat pump type so I will keep looking for a unit with a long warranty.

 

[LeftieBiker]

Our municipal water system uses adjustable pressure valves at the meter. Ours failed once and had to be replaced, but that was once in 30+ years. The expansion tank definitely helps - no more water hammer effect when we open faucets.

 

[goldbrick]

I read that most modern hookups include a backflow prevention valve on the incoming water supply I don't know how accurate that is but in my case, there are multiple backflow prevention valves in place since I have a tankless heater that supplies both domestic hot water and heat for the house and the backflow prevention valves are needed to make the flow sensor in it operate correctly. I also read that some pressure reduction valves include a 'bypass' to allow water to flow backwards to prevent this type of problem but once again, I don't know the accuracy of that or the details. But in general, I completely agree that in older systems without a backflow prevention valve the pressure built up by the hot water expansion will simply flow back out of the house.

 

[Oilpan4]

If you have hard water and a gas water heater the scale will settle to the bottom and the scale will cause hot spots, those hot spots will boil, boiling causes cavitation, then cavitation causes metal fatigue and eventually the tank will crack.
I have to drag the hot water heater outside and flush all the junk out of it about every 2 to 3 years.

 

[Kieran973]

By the way, I went with the 65 gallon Rheem Professional Prestige. This is a professional/contractor grade model that is allegedly different in important ways from the ones they sell in the box stores. $3150 for tank + installation after all rebates, but this includes some re-piping, capping the natural gas exhaust, running a new 30 amp circuit from the panel to the water heater, and installing a thermostatic mixing valve. Skilled labor is expensive in my area. Installing a regular electric water heater would have cost ~$2500 and simply replacing the gas heater with a new one would have cost ~$1800. With solar, the heat pump water heater compared to either pays for itself in 1-3 years. Now hopefully it just doesn’t break. Anyway, thanks everyone for your input.