Here's probably the best 'how-to' for an improved instant, on-demand hot water system I've seen. It was in a recent edition of "Fine Homebuilding" magazine.
Here's link too.
Here's link too.
Automated Recirculating Hot Water System
- Thread starter johnnynine
- Start date
Nice read, but his solution seems to be turning the "On-Demand" system into a complicated "Storage" one.
Brian
drozwood90
Senior Member
I went with a 175,000BTU GAS BOSH tankless unit, rated for an apartment complex. With that "overkill" and having 3/4" feeders (for hot and cold) I have NOT experienced ANY of the issues they speak of in that article.
I have "old" style valves in my house (which means cold slugs and hot slugs get passed on to the person in the shower), and I have taken a shower, while my wife ran the laundry, at the same time she turned on the dish washer (I was experimenting on purpose with ME in the shower she SHE wouldn't get the hot cold hits).
All seemed well. While all that stuff was running, I asked her to turn on a few faucets and then turn on the faucet for the tub in the second floor bathroom. No issues. Had I had the new pressure controlled valves I don't think I would EVER have an issue on any of this stuff.
You just need to make CERTAIN that the unit is plumbed (gas wise) properly! If it can't get the fuel, it can't heat properly!! I ended up running a new 1" line to get the 175,000btu of gas to the tank. And guess what? IT worked!
--Dan
huggy59
Active Member
Another suggestion would be to use a small on-demand (electric?) water heater at the point of use (for example, supplying the master bath), which would only heat on-demand until the water in the pipes from the remote hot water system heated up enough.
IMO, to save energy ($$$), you'd set the temp at the local heater a bit lower than that supplied from the main or remote water heating system so it would shut off after the supply water was hot enough (whether the remote system is storage or on-demand). You'd get quick hot watter in the bathroom from the local on-demand unit until the water and pipes heated up sufficiently. Then you only pay for heating water at use.
IMO, to save energy ($$$), you'd set the temp at the local heater a bit lower than that supplied from the main or remote water heating system so it would shut off after the supply water was hot enough (whether the remote system is storage or on-demand). You'd get quick hot watter in the bathroom from the local on-demand unit until the water and pipes heated up sufficiently. Then you only pay for heating water at use.
Steve
Senior Member
Warning - this is an old thread (so beelzerob doesn't yell at me)
So, has anyone perhaps used one of these Redy Temp recirculators, or maybe the Metlund unit?
Steve
Senior Member
A POU water heater was the other option, but it will be using electricity all the time keeping water hot just like the main tank. Both solution require power so that's a wash. The pro to the water tank is the water will be there instantly with zero wait and no user intervention. With the recirculator you need to trigger the on demand either by button, timer, PIR, etc. But, the recirculator only runs for a minute or two at a time when you tell it. The other advantage to the recirculator is when you put it on the furthest sink, any other water outlets on the same line also get the hot water. Plumbing on either system will be about the same too.
I put in low voltage wires from the bathroom to the water heater area when the house was built and had an extra pipe put in for a circulation pump. I put a push button in a wall. When we want hot water we just push the button. A pump runs for 45 seconds to bring up the hot water (it starts to get warm much sooner but I have 1" pipes so lots of water to replace). My wife wasn't too sure about it at first but she thinks it's great now. Nice thing is that we don't waste energy (and $$) to heat the pipes when we don't need it. The water heater is a tank type 135,000 BTU unit that also supply heat to the radiant floor (through a heat exchanger as required by code). The only issue so far is that the floor heat AND shower at the same time can drain the hot water. I plan to add another relay to the timer board (a PIC processor) to disable the floor heat for an hour when the button is pressed. No one will miss an hour of floor heat (concrete floor with lots of thermal mass).
The other thing I have is a drain heat recovery unit. Lots of energy in the warm drain water from a shower. This unit claims to recover something like 60% of the energy. No moving parts and it does work VERY well to preheat the water into the water heater giving more hot water and keeping the cost down. I think who is manufaturing them for GFX has changed and the design has changed a little but check here:
http://www.gfxtechnology.com/
BTW, I got mine before copper prices went crazy. The prices are a lot higher but energy prices have gone up too...
The other thing I have is a drain heat recovery unit. Lots of energy in the warm drain water from a shower. This unit claims to recover something like 60% of the energy. No moving parts and it does work VERY well to preheat the water into the water heater giving more hot water and keeping the cost down. I think who is manufaturing them for GFX has changed and the design has changed a little but check here:
http://www.gfxtechnology.com/
BTW, I got mine before copper prices went crazy. The prices are a lot higher but energy prices have gone up too...
This is exactly the configuration we went with in a fairly large (6,000 sqft) custom home. We actually used 2 Rinnai tankless heaters (in series) with a small 6 gallon electric storage tank. A recirculating pump cycles hot water from the storage tank through a loop that runs the length of the house.
We really needed the recirculating loop because the house is very long (110') and we would be running a lot of water "down the drain" waiting for hot water to reach the taps. In addition, tankless heaters do have a little start up lag time (the "cold water slug"). Finally, you don't really want the tankless heaters cycling on and off when you are running water through the recirculating loop.
While we lose a small amount of efficiency due to the storage tank, the benefits of the system far outweigh the negatives. The system works flawlessly. We get hot water almost instantly at any point in the house. Once hot water is called for, the tankless heater(s) will fire to replenish what is being drawn from the storage tank. When there is no demand, the tankless heaters never run - even though the recycling pump is running.
We have run a bunch of hot water demand at one time and never come up short - including filling a large jacuzzi tub with a very high flow fill valve! It's actually pretty neat to watch the Rinnai's communicate - the second unit won't fire until the demand exceeds the heating ability of the first unit.
The recirculating pump was originally running on a timer set to come on before I woke up and back off mid-evening. I've since replaced that with an Insteon ApplianceLinc that runs off an ISY-99i. It runs the recirculating pump for 5 minutes every half hour.
- Rick
I have been wanting to put in a recirc system for a while but I do not have a return line. I would rather have the pump at the water heater but I also want it to be an on demand system controlled by a switch someone can push before they take a shower. I'm wondering if the temp-controlled remove valves are a problem in this situation as I assume they work this way: when they open, the pump senses the pressure drop and starts running until they close and the pressure rises again. So if the pump is switched off but the valve remains open, what happens? I guess the chili pepper pumps are a solution to this problem because the pump is at the eol but if they are noisy that's not a good solution.
Steve
Senior Member
I have found that the Grundfos and Laing systems have the pump at the water heater, but they are more times and not on demand. The RedyTemp and Metlund systems are more on demand. From my research the Chilipepper is kinda noisy and crappy but the RedyTemp and Metlund are much higher quality and quiet. I am leaning toward the Metlund at the moment. Neither the RedyTemp or Metlund units require a return line. The only down side to these are you need an outlet by them (not a problem for me since I'm remodeling that room) and if you have multiple fixtures but they are not plumbed in a series fashion. If in series and putting the pump at the last one, it will provide hot all throughout. But if you have several branches you may need multiple units.
Wow !
By the time you add in the costs of running the 110v electric water heater and the 110v circulating pump and the high cost of the tankless heater and additional plumbing work (plumbers aren't cheap) I think you have pretty well eliminated any savings of going tankless.
I thought the point of going tankless was to save energy costs ?
Wouldn't it be a lot cheaper to just keep your old water heater ?
By the time you add in the costs of running the 110v electric water heater and the 110v circulating pump and the high cost of the tankless heater and additional plumbing work (plumbers aren't cheap) I think you have pretty well eliminated any savings of going tankless.
I thought the point of going tankless was to save energy costs ?
Wouldn't it be a lot cheaper to just keep your old water heater ?
If you lose a small amount of efficiency due to the storage tank you have to loose some for the 110' loop you keep hot (or at least warm) all the time. Even if you insulate it very well it has a lot of surface area. If the heaters don't start the circulation must cool the storage tank - maybe not sufficiently to be an issue. Or maybe you draw water often enough to keep the tank hot. Either way keeping the loop hot uses energy that somehow must be supplied by the heaters.... Sounds like it is very effective but I don't think it is as efficient as you think.
All very accurate and valid observations! Without being defensive about it, let me go through a little of the thought process behind our design decisions. Your ultimate design will reflect your personal desires and concerns, the size and design of your house, and your location! Without going down too much of a rabbit trail, I did a ton of homework on all our systems decisions (ex-engineering background kicking in)!
The thread has done a pretty good job of showing that everything in residential home design is a trade-off! We definitely had some specific criteria in mind with respect to the design of our hot water system, and absolute energy efficiency wasn't our #1 criteria. Depending on what's most important to you, you could end up with a very different system design! We live in a part of the country (North Carolina) where domestic hot water isn't commonly used for heating (we use high efficiency heat pumps since we require as much cooling in the summer as heat in the winter), so a lot of our criteria related specifically to personal hot water use needs.
- Not running out of hot water was probably the #1 criteria! With hot water loads that vary wildly (depending on how many kids are home and how many friends come along to spend the week-end), I can absolutely say that we don't ever run out. This has a huge WAF - especially when she wants to draw a bath in the jacuzzi tub and is able to fill it in 5-7 minutes (given the high flow rate fill valve) with comfortably hot water! A trade-off between absolute efficiency and luxury? No argument here but hot water is one of those things that you take for granted until it's not there!
- Given the size of the house, to omit a recirculating loop would mean extremely long "wait" times to get hot water in most areas. I previously lived in an older house where we had to run faucets at the "far end" of the house 3-5 minutes to get hot water. Running that much water down the drain is pretty painful, and more than a little inconvenient! Any way you design a recirculating loop it isn't as energy efficient as not loop! In our case, the recirc pump doesn't run all that much, the recirc piping runs through conditioned spaces (and is insulated for what it's worth), and the small back-up tank draws pretty modestly. Retrofitting an existing home with a recirculating loop is typically pretty tough, but we were looking at new construction and the additional return run for the loop was a very small cost item!
- We live out in a pretty rural area and can (and do!) lose power - sometimes for extended periods (we are prone to ice storms). I wanted a system that would operate with a very low power load on our generator, and propane fired tankless heaters work extremely well. We lose the recirc pump electric "back up" tank, but having any hot water when the power craters is almost priceless!
Conventional tank heaters were never a consideration for me! There are too many negatives in my mind given our specific needs - capacity limitations, energy requirements on the generator, physical size, passive losses, etc. Will our system "pay for itself" versus other design options - tough to tell! Does it do exactly what we wanted it to do in our situation - again this is a big "yes"!
Point of use heaters also wouldn't meet our needs, because there are a lot of "demand points" to satisfy including tubs and showers! If we were in an existing home this could be a valid option, especially if there are only a couple of sinks that needed a "boost".
Sorry to run on so long on this, but it's a great example of how complex design trade-off's can be in home design - and how there are a lot of good answers to every problem! We had the ability to work with a blank canvas on our project and spent a lot of time evaluating each piece of the puzzle. Building a new house vs retrofitting an old one is a very different process, and clearly a lot of our decisions would have been different if we were doing a remodel! The fact that we plan to be in the house for a very long time also came in to play in a lot of areas. I clearly wouldn't have gone as "overboard" in a lot of the areas we did if I was only going to be in the house for a few years.
Enjoy the decision making process and rely on your team of sub-contractors for their input! A lot of things that look good on paper don't necessarily translate so well when it's time to come up out of the ground with the thing!
- Rick
