Low hot water pressure in upstairs unit

[Cody Thompson]

I have have a duplex that was converted into 4 units. The added upstairs unit has very low hot water pressure because the hot water heater to all units are in the basement. Any suggestions or contraptions I may be able to install to remedy the situation??

[Bill S.]

@Cody Thompson not sure where to begin but I do water for my W2 job and there is some serious misinformation here. Don't want to bust any chops so I'll just state what I know and let you draw conclusions. 1 psi of water pressure is 2.307 ft of change in elevation. That said a building 23 feet tall will have 10 psi less pressure at the top then the bottom. I say that because it's not probable that the elevation difference between the upper and lower units will result in the perceived lower pressure. Assuming the kitchen faucet in the lower unit is probably only about 10 ft lower than the one in the upper unit you would have maybe 5 psi pressure difference due to elevation. 5 psi or even 10 psi difference at normal operation pressure (50-70 psi) is indiscernible to most people.

Most municipal water systems are designed to provide at least 50 psi during anything but fire flows. 20 psi is the EPA required minimum pressure in the City distribution system during a fire flow situation. So while it's possible that it's a problem of supply from the City that is very unlikely.

If you are on a private system or well. All bets are off and you need to investigate that too.

Based on your statement that it's the hot water, I assume you are not having a problem with the cold water. This means your problem is in the piping between the hot water tank and the upper unit. An easy way to check your problem is to buy an inexpensive pressure gauge at HD or other big box store. Hunt through the brass fittings there and cobble together fittings so you can attach that pressure gauge to a faucet or shower in the unit (Hint: the screens in the end faucet unscrew as does the shower head). Attach the pressure gauge to the faucet and turn on the hot water (make sure there is no other water use in the building while performing these tests). Note that no water will flow but the pressure in the line will read on the gauge. Next open another hot water faucet in the same unit and, while it's running, read the pressure. The different between those two numbers is the friction loss in the pipes from running water. Losses above 10 psi are significant and you have a piping issue.

If the property has galvanized pipes it's likely that the hot water pipe has corroded. Hot water corrodes faster than cold water. Horizontal runs corrode faster than vertical and those closest to the tank corrode first. I removed a water heater that had a 6" length of 1/2" galvanized pipe right off the water heater that when I removed it was so corroded that I could not see through it when holding it up to the light.

Also look for partially closed valves. Perhaps the valve under the sink got closed for repairs and wasn't opened all the way or has some debris caught in it. Perhaps there is a hot water shut-off to the unit that is an old style gate valve that got a piece of debris caught in it, wasn't opened all the way, or has corroded.

Pex with a manifold home run system is a good replacement option if it's a pipe issue. Also all valves should be full port ball valves (full port means when they are open the area is the same size as the pipe).

If you want to add pressure to a line you must add a pump (something that adds energy). Tanks (most have bladders to separate the air and water otherwise the air goes into the water and after time, you have no air in the tank) are storage devices and offer two things. Storage and surge/expansion protection (Neither will add any energy needed to increase pressure). The smaller tanks on hot water heaters are expansion or surge tanks. Some water systems have backflow preventers on the line so when a hot water tank fills with cold water and heats up it expands slightly. If the system is completely "tight" (no faucet drips) then it could rupture something. The tanks have a bladder that separates the air and water (they come pre-charged) so that the air compresses when the water expands. These tanks also absorb energy resulting from stopping the flow of water quickly (surge). It's the knock you hear in the line when the dishwasher stops filling or the washing machine stops filling. It's like the noise you hear when a freight train stops and the little bit of slack in all the couplings between the cars is taken up. These are pressure spikes that can damage your piping. The air tank acts like a shock absorber so you don't get the knock.

The larger tanks they generally use on wells are for storage so that every time you use water your well pump doesn't have to come on. The pump turns on at low pressure and fills the tank to a higher pressure, compressing the air (it also has a bladder to separate the air and water) with water. When the high pressure point gets reached the pump turns off. When you open the faucet the air pushes some of the water out until you turn off the faucet. As the water moves out the pressure decreases slowly until the low set point is reached and the well pump turns on.

Realize this is bit long. Hope it helps.