Hot & Cold water pressure

[Cathy and Paula]

Why is there a difference in the water pressure between the cold water and the hot water? When we are using our water pump the cold water keeps the pump running correctly but when we turn on the hot water the pump sputters. I talked with the shurflow people and they told me how to adjust the pump but even if I adjust the pump there is still going to be a difference between the hot and cold pressure. Does the hot water line have some type of suppressor on it that can be removed?

Thanks

[Kirk W]

The difference is due to the hot water actually being the same water from the tank as cold, but it has to pass through the water heater which inserts a big container of water volume with an air bubble at the top. When you leave things sit for a long time the two tend to equalize to some extent, but as soon as you turn on the faucet the water heater's tank comes into play. If you take a shower and use a lot of water, then let things sit with no water use until the water heater shuts off, then open a faucet it will surge momentarily due to the increased pressure inside of the water heater because the cold water has expanded inside as it increased in temperature but with all things equal and water running, how will typically be somewhat lower in pressure due to the resistance of passage through the water heater. To some extent that is also true when on city water or in a house, but with the much larger water supply it is not usually noticeable.

 

There could also be some sputter in the hot if there is too much air in the water heater's tanks as it will vent out with that water, and also there could be occasionally a little steam bubble in the exiting water. The only thing in the water line from the water heater that isn't typically found in the cold is a check-valve at the outlet of the tank which may introduce a slight pressure drop, but it is important to be there to prevent back-flow of the hot water.

[Pat & Pete]

When we flush our water heater , about twice a year , simply refill the tank until water shoots out of the relief valve toward to top of the tank , which I flip open prior to the refill and flip shut when full . That seems to leave enough of an air pocket and our pump does not sputter .

[Cathy and Paula]

We have the tankless water heater, does that make a difference?

[Clay L]

I t could. Some slow the flow down to get the water hotter.

[Kirk W]

It likely could, but I have no experience with one of them of my own. Neighbors have one in their house and when I asked them they do say that there is a detectable difference in water pressure when full on with only hot or only cold, but not a great one. Most city systems are operating at both a higher pressure and a higher volume capability so the impact is probably less. With the tankless, you don't have any air bubble in the top to worry about so that isn't a factor. It probably does have a check valve at the exit, but I'm not certain of that either. I would expect some pressure loss through the extra area provided by your water heater, but am only guessing as to what effect it would have. Perhaps someone on the forums who has a tankless water heater will chime in.........