Can I tee off of a 3/8" PEX so that it supplies 2 sinks?

[Lithnights]

I have PEX throughout my home, all fixtures with homeruns. Most are 3/8", bathtubs and outside spigots are 1/2". Pressure has always been fine.

I had a recirculating pump installed and want to use it for my kitchen sink and powder room sink (about 20 feet away from kitchen). All PEX is accessible in basement.

I want to keep the existing 3/8" PEX to the kitchen sink and tee in the existing 3/8" PEX that feeds the powder room sink. i.e. one 3/8" from manifold, to feed 2 sinks. This will allow me to use the reciurculator more efficiently since the powder room sink will be able to use some of the hot water in the kitchen sink pipe... i.e. it will only have to flush out a small amount of cold water before the hot water gets there. SEE ATTACHED PICTURE.

It will be rare that the kitchen sink and powder room sink are used at the same time, and if they are, we're OK with a temporary drop in pressure. We feel the cost savings of keeping the 3/8" instead of switching to 1/2" would be worth it. We have pricey propane so don't want to have to heat twice as much volume, using 1/2". Also, the existing powder room sink only has a 1 gallon per minute flow to it anyway.. which we're totally fine with. Not sure if that's typical or not..

Thoughts?
Thanks in advance!

 

[Reach4]

You seem to have the issues figured out.

The load that feeds off of the side port of the tee will have more restriction than the straight-thru path.

 

[Sponsor]

 

[Jadnashua]

Sounds like you may have access to your PEX tubing...if you want to save some money, consider insulating the hot lines and return. That will tend to save you some money.

Depending on the type of recirculation system you have, you might also save some if you put the thing on a timer if it now runs 24/7.

 

[Lithnights]

You seem to have the issues figured out.

The load that feeds off of the side port of the tee will have more restriction than the straight-thru path.

Yes that makes sense. That side port would be the powder room, which is used way less than the kitchen sink (straight thru path), and almost never at the same time.

 

[Lithnights]

Sounds like you may have access to your PEX tubing...if you want to save some money, consider insulating the hot lines and return. That will tend to save you some money.

Depending on the type of recirculation system you have, you might also save some if you put the thing on a timer if it now runs 24/7.

Yes I do have access in the unfinished basement, but not for long since we're finishing it and drywall goes up next week. In fact, we've already changed the way the recirculation works, it now uses a 3/4 line mostly across the basement, then tees off to the kitchen, bath shower and sink and sink. After realizing how much water is getting heated and recirculated yet not used, we now realize we need to adjust it again. That's why I want to change it to just use the kitchen sink, since we now realize THAT is the priority for quick hot water.

It IS on a timer, but it's currently designed in a way that impacts the kitchen sink (used often throughout the day and night..we work from home, even pre Covid), as well as impacts the master bath shower and 2 sinks (which are rarely used). So if we set up the timer for 2 hours in the morning, and 2 hours at night, that's great for bathroom but terrible for kitchen (we now wait 3x as long for hot water as we did before the recirculator since it's flushing out cold water through 3/4 pex instead of 3/8 pex). If we set the timer so it runs a lot more, that is great for the kitchen sink but a complete waste of water that gets recirculated up to the far away bathroom and back again... all day.

 

[Jeff H Young]

beside being on a timer why not a thermastat as well?I allway put both no need running pump for 2 hours at a time is there? never seen 3/8 in a house

 

[Lithnights]

beside being on a timer why not a thermastat as well?I allway put both no need running pump for 2 hours at a time is there? never seen 3/8 in a house

In a typical scenario, I would tend to agree that a thermostat would help. But in our situation, we simply don't know when the kitchen sink, or bathroom shower or sinks, will be used. It could be used at 9:00 and 9:30 one day, 11:30 and noon the next, 1:00 p.m. and 2:00 p.m. the next etc. Bottom line we use that kitchen sink about a dozen times a day, and it could be at any time. We shower at all different times.. there is no schedule unfortunately, which lends itself to bad news for a recirculator IMO.

Our house was a new build, and they ran a home run manifold system. 3/8 for everything except showers and outside spigots which have 1/2. For years I thought, why would they do this? Why not just do trunk and branch? But looking back, using 3/8 gives us enough pressure, and uses 1/4 of the water as a 3/4 line would. Thus less cold water to flush out to get to the hot, and one quarter of the hot water to sit in the pipe which just cools down.
I didn't really think about any of that, until we changed to a 3/4 line last week for some of the fixtures. Because it increased the wait time drastically for hot water when the recirculator pump isn't on.
Thanks!

 

[Jadnashua]

Many of the engineered recirculation systems use an aquastat to adjust the recirculation. Many systems don't circulate the water constantly, and only enable it once the desired monitoring point gets to warm. The system I have, shuts the pump off when its sensor reaches 95-degrees. Some do it at 105, and some are adjustable and their pump runs, but with the valve(s) closed, there's less waste energy. This gets nearly hot water at the sensing point with hot near by. The energy loss is worst when the temperature delta is higher, so stopping it once it gets nearly hot is worthwhile. Some use a valve to stop circulation, and some turn the pump off. The system I have shuts the pump off so it only tends to run for maybe a minute every 15-minutes or so but longer the first time it comes on, and shuts off at 95-degrees. That sensing point happens to be in my master bath vanity, while the shower is closer to the WH, so is warmer. First time in the morning when it runs, it may need a bit over 2-minutes to reach temp, and shut off. The pump itself is only 9W to keep the flow rate down which helps with the longevity of the WH and the pipes.

When you consider the energy used to heat the water and what you throw out without recirculation, if you can minimize the heat lost when it is just sitting in the pipes, it can save energy. Say it takes 2-3 gallons down the drain, that's 2-3 gallons of hot water you paid for that you didn't use, and that amount less in the tank once you decide to use some once it arrives. People sometimes lean towards a bigger pump, which uses more electricity, to get the hot there quicker, when using an on-demand system.

 

[Lithnights]

Many of the engineered recirculation systems use an aquastat to adjust the recirculation. Many systems don't circulate the water constantly, and only enable it once the desired monitoring point gets to warm. The system I have, shuts the pump off when its sensor reaches 95-degrees. Some do it at 105, and some are adjustable and their pump runs, but with the valve(s) closed, there's less waste energy. This gets nearly hot water at the sensing point with hot near by. The energy loss is worst when the temperature delta is higher, so stopping it once it gets nearly hot is worthwhile. Some use a valve to stop circulation, and some turn the pump off. The system I have shuts the pump off so it only tends to run for maybe a minute every 15-minutes or so but longer the first time it comes on, and shuts off at 95-degrees. That sensing point happens to be in my master bath vanity, while the shower is closer to the WH, so is warmer. First time in the morning when it runs, it may need a bit over 2-minutes to reach temp, and shut off. The pump itself is only 9W to keep the flow rate down which helps with the longevity of the WH and the pipes.

When you consider the energy used to heat the water and what you throw out without recirculation, if you can minimize the heat lost when it is just sitting in the pipes, it can save energy. Say it takes 2-3 gallons down the drain, that's 2-3 gallons of hot water you paid for that you didn't use, and that amount less in the tank once you decide to use some once it arrives. People sometimes lean towards a bigger pump, which uses more electricity, to get the hot there quicker, when using an on-demand system.

I agree with everything you say. My system is a Rinnai and I've spoken to their tech guys multiple times about this. My system works very similarly to what you describe, 98° at the thermal bypass valve and it shuts it down.
I have actually stood by for 30 minutes at one point to get an idea of how often it runs. the main problem is I simply can't predict how much energy use it would use, but I don't want to take that chance because once the basement ceiling is installed, there is no easy way to change the piping size.
I am sure it is fairly efficient for what it does, if on a short schedule, but the concern for me is that I would be heating up water for that master bath throughout the entire day (to allow me to get instant hot water in the kitchen all day) when it simply isn't needed..
I agree the electric use is minimal, it's the expensive propane used concerns me.
And the water down the drain does not concern me, I have figured out that a gallon here costs about half a penny. That is peanuts compared to the propane cost from what I've researched.

Bottom line, I don't mind the concept of the recirculator pump for that kitchen sink which we use often. I just would like to use the small pipe (3/8)as possible to minimize the energy use. And if I can incorporate the powder room sink as well (using a 3/8 tee), that would be a bonus.

Thanks!

 

[Jadnashua]

Probably a bit over half the year, you're heating the house, so any heat loss from the pipes is going into the room(s), so is not actually lost. Using some insulation on the tubing should minimize how much is lost.

You're missing some about throwing the water away while waiting for it to get hot. The water going into the line is hot that you paid for, so say it takes three gallons to get hot to the sink/shower/whatever, that's three gallons of water you've paid for to heat the didn't get used as hot, and means you'll have to heat those three gallons back up in the tank, and have decreased the volume of water available to take that shower, fill the tub, or do the laundry. Circulating the somewhat warm water back into the tank so it can be rewarmed, if you can minimize the heat loss into the room with some insulation ends up using less than you might think. You may be paying a separate charge for the waste water, too, not counting some places (maybe not PA) where water is a dear commodity, and not a good thing to waste regardless of what it costs monetarily.

If you really want to save, you'd put up with an on demand system but have to wait for it to work each time you wanted water and activate it manually rather than having it available all of the time during your time window(s).

 

[Lithnights]

Probably a bit over half the year, you're heating the house, so any heat loss from the pipes is going into the room(s), so is not actually lost. Using some insulation on the tubing should minimize how much is lost.

You're missing some about throwing the water away while waiting for it to get hot. The water going into the line is hot that you paid for, so say it takes three gallons to get hot to the sink/shower/whatever, that's three gallons of water you've paid for to heat the didn't get used as hot, and means you'll have to heat those three gallons back up in the tank, and have decreased the volume of water available to take that shower, fill the tub, or do the laundry. Circulating the somewhat warm water back into the tank so it can be rewarmed, if you can minimize the heat loss into the room with some insulation ends up using less than you might think. You may be paying a separate charge for the waste water, too, not counting some places (maybe not PA) where water is a dear commodity, and not a good thing to waste regardless of what it costs monetarily.

If you really want to save, you'd put up with an on demand system but have to wait for it to work each time you wanted water and activate it manually rather than having it available all of the time during your time window(s).

Yes I have looked at it from the "it's heating the house" angle but I still have concerns about the efficiency of that heating, and like you said, that only applies during part of the year.. for me, our heat is only on 4 months of the year, and I have to assume that our heat pump is wayyyy more efficient than what is essentially hot water pipe heating.

And you're right about the heating the 3 gallons or whatever. I calculated our total water/sewer bill for a 6 month period and water AND sewer (which is 3x water!) TOTALS 6/10 of a cent per gallon. I.e. for me, water waste is peanuts. I'm as environmentally concerned as the next guy but that water waste is miniscule compared to my propane costs.

I would love to have a demand system (if it was just me), where we'd wait that 45-60 seconds to get hot water, but at least there's no water waste, but I just don't see that happening with my wife and 3 kids... manually activating it would NOT work with them.. LOL.

SO with all this said, I think I understand the pros and cons of the recirc and I think what I have planned is going to work best for MY family. But the question remains..in order to do this, IS IT OK TO TEE OFF OF A 3/8" LINE if I'm willing to risk any potential temporary loss of pressure?

Thanks!

 

[wwhitney]

Yes, the only downside is reduced pressure.

Cheers, Wayne

 

[Lithnights]

Yes, the only downside is reduced pressure.

Cheers, Wayne

Good to know. I typically might have a concern about that but with it being a powder room (low flow as it is) sink, I have to think I could live with that reduced pressure for the rare times it would occur, in order to benefit from the advantage of having it hooked up to the recirculator.
Thanks!