Time for Hot Water to Faucet and Water Heater Location

3 years ago

We are working on a very 'long' (wide) new house design. The hot water heater is at one end in a utility closet off the garage and the master suite with bathroom at the opposite end - a straight line distance of about 85 feet via a continuous PEX run thru the slab. (the actual line would be a bit longer w/ some bends/curves - 95 to 100 ft let's say)

What kind of 'wait time' will we be looking at to get hot water to the master bath?

Would it be long enough to warrant considering an alternative like a 2nd hot water heater?

Would the selection of a 'tankless' heater vs a traditional tank heater further impact this?

Thanks!

Featured Answer

Jake The Wonderdog

3 years ago

last modified: 3 years ago

100' of 3/4" PEX pipe holds about 1.8 gallons of water. You would have to run a bathroom sink almost 2 minutes before it would start to get warm.

A small electric tank heater VERY near (In) the bathroom would provide nearly instant hot water to the sink for washing your hands or shaving. The link is to a 6 gal unit.

These small units are slow to recover, so you want enough storage to take care of hand washing, etc. At 6 gallons it will also have enough storage to buffer the initial almost 2 gallons of cold water in the pipe when you are taking a shower until the hot water from the main unit takes over.

Electric resistance is the most expensive way to heat water. However, a small point of use heater in series with a gas tankless or electric hybrid would save both energy and water when the main heater is far from the master bath.

Copper pipe has a slightly larger inside diameter than PEX. That same 100' of 3/4" pipe in copper would store about 2.5 gallons of water instead of 1.8 for PEX. In addition to the water in the pipe, the thermal mass of pipe has to warm up, and then if it's not insulated and in a slab (not code) the copper is going to conduct the heat more readily to the concrete than PEX. For those reasons I'd say copper will take longer to get hot water than PEX.

I want to again say that the best solution is not to have a water heater 100 feet from where the water is being used. Be sure to insulate the hot water line in the slab to R5 - not the R3 pipe insulation you find at the hardware store.

Sort by:Oldest

Comments (7)

nycbluedevil_gw
3 years ago
I have your situation. Not sure of distance but house is 3,500 sf, two floors, master upstairs on other end of house from utility room off the garage. Wait time is about five minutes, maybe a bit less. Big waste of water but at least we are on a well.
PRO
HALLETT & Co.
3 years ago
Why are you planning this? Put the water heater in the center of the house- presumably a tankless unit in the attic. Alternatively a circulated pump on a timer will give you hot water on demand
Related Discussions
Hot Water Heater Expansion Tank & Water Softener
Q
Comments (7)
Fixing the running toilet fixed the usage problem and the softener appears to be functioning perfect, which I guess begs the question, is it OK to leave the check valve in? It does not appear to be restricting flow in any way (valve shows maximum SFR to date of 13.9 gpm) and I don't think it is creating any back pressure. Wouldn't the check valve actually prevent any back pressure from reaching the valve and resin tank and in turn protect the resin tank and valve? Say for instance that the expansion tank was malfunctioning for whatever reason, and the water heater kicked on and created a brief expansion that drove the psi up to say 150 psi and that back pressure pulse was pushed back to the check valve since the expansion tank didn't work correctly. Wouldn't the check valve slam shut and prevent this back pressure from reaching the resin tank and valve? If the normal line pressure on either side of the check valve is the ambient 60-70 psi of the system under normal conditions and a back pressure pulse of 150 psi comes from the water heater side of the installation, isn't that precisely the set of conditions that would cause the check valve to close and keep the pulse on the water heater side of the system? I realize that with check valve in place and the theoretical malfunctioning of the expansion tank, the pressure pulse will seek some method of escaping which could cause damage somewhere in the house like a faucet or toilet, but at least it will not have blown the resin tank or destroyed the control valve, correct? I hope this rationalization makes sense, but I'm not sure that I have done a very good job of positing my questions or explaining the scenarios. Oh well. Take a swing at it if anyone feels like it. I am interested to hear some opinions on this one. I'm thinking more potential bad will come from disassembling a functioning, dripless install than from keeping the check valve in place. Thanks. Drew
...See More
Air in hot water heater and hot water faucets
Q
Comments (16)
I have exactly the same problem. I have no idea how the air gets into my hot water lines . I recenlty installed a new hot water tank and its a simple one for one.I never had this problem before but now each morning I have nasty burps at the faucet I first use . Its great for the rest of the day but only in the morning do I get the trapped sputtering air. I do have an existing Vacuum relief valve attached to the cold intake line to the Hot water tank and itys probably 25 to 30 years old there is no leakage but could this somehow be allowing air into my hot water tank.? I am also scratching my head.
...See More
Hot Water heater - water flow?
Q
Comments (1)
Only solutions would be 1) dedicated heater closer to the shower or 2) recirculation pump for "instant" hot water. Economically, neither would work. Both would likely cost you much more in installation and energy use than your water savings. Especially for retro-fit, doubting that your water lines are insulated, your energy-use increase could be significant.
...See More
Hot water heater doesn't seem to hold a lot of hot water
Q
Comments (5)
"When you think about it 40 gallons isn't a lot of water." I disagree. That is a lot of HOT water at 140Â°. If you were to draw it all down at 2.5 GPM, it would take 8 minutes. ThatÂs theoretical, because the way you draw it is to push it with COLD water. But thatÂs OK, because you arenÂt going to take too many showers at 140Â° Â one, maybe. So to make it comfortable, you mix in 40 gallons of water at say, room temperature, and now you have 16 minutes at 102Â°. All the time, the fire is burning in the heater. If you have not been drawing a quart of water from the bottom of your heater once a month (And I know you havenÂt.) then you may have a scale at the bottom. This fools the thermostat into thinking you have many gallons of hot water, when all you have is a thin scale of hot deposits. Pinoke
...See More
Seabornman
3 years ago
I would plan on adding a recirculating line under slab. Our kitchen sink is 45 feet away from WH and the wait for hot water is a nuisance.
PRO
Patricia Colwell Consulting
3 years ago
Do on demand hot water where you neeed it or do another plan with the water heater in the center of the house .I have 75’ long house with kitchen near one end and master suite at the other but the water heater is in the center of the basement along with the boiler for heating.
Jake The Wonderdog
3 years ago
last modified: 3 years ago
This plan is always terrible. I remember one person on here who NEVER got hot water to his master bath shower because of the long run AND it was uninsulated in the slab. All of the heat dissipated to the slab before it got to the shower. If he filled the tub( 4gpm) it got warm - but the shower (at 2.5 gpm) didn't.

If you must do this, install a small tank heater in the bathroom area in series with the main unit and do major insulation of the run in the slab. Do a calculation on how much water in this line and make sure your small tank heater has about 2x that capacity.

If you run a circ pump on this setup you will be heating the slab the entire time.

And yes, a tankless heater adds about 10-20 seconds on to that wait time.
HU-412631568
Original Author
3 years ago
@Jake The Wonderdog

Wow - thanks for the suggestions!

This is interesting. A small tank would be electric and thus no need to run gas or vent like the tankless gas heater way back in the GA - I like that.

The 2X capacity is to not allow the cold water in the line overwhelm the tank heater during extended usage I'm guessing.

Off topic but Related Question:

Our CURRENT home has a gas tank hot water heater in the garage and about 35-38ish feet of copper in the slab to the kitchen. It takes a long time to get hot water to the kitchen, up to 3 minutes. (we turn it on and usually expect get distracted doing something else waiting as the water runs...) I assume it takes a while as the cold copper in the cold slab absorbs the heat from the water until it is sufficiently warmed up even in this seemingly short run.

Question: Does Copper make my situation take LONGER for getting hot water than PEX or no effect?

thx

Time for Hot Water to Faucet and Water Heater Location

Jake The Wonderdog

Comments (7)

nycbluedevil_gw

HALLETT & Co.

Related Discussions

Seabornman

Patricia Colwell Consulting

Jake The Wonderdog

HU-412631568
Original Author

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US

Time for Hot Water to Faucet and Water Heater Location

Jake The Wonderdog

Comments (7)

nycbluedevil_gw

HALLETT & Co.

Related Discussions

Seabornman

Patricia Colwell Consulting

Jake The Wonderdog

HU-412631568Original Author

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US

HU-412631568
Original Author