Hot Water Recirc with Insulated Lines -- is it really that inefficient / expensive?

bryantroll

I've read up on hot water recirc and most of the discussions end that its too expensive / inefficient / not a great idea. I'm also guessing that most of these scenarios don't have fully insulated lines.
By my math, it shouldn't increase monthly energy costs by THAT much -- am I wrong?

Scenario would be:
-new Radiant underfloor heating for main floor and ceiling radiant for basement
-4 bathrooms with up to 8 people in the house at a time
-easiest / least expensive solution is a Combi unit for radiant heat and domestic hot water which would be located across the house from the bathrooms, roughly 45' away
-I really don't want to have to wait 90 or 120 seconds or more for hot water, if I can avoid it
-I have full access to basement ceiling and am running all new PEX domestic water lines, and can insulate them as needed

I am trying to finalize design on an all new heating and how water system -- decisions include:
1) Combi unit vs separate units?
2) HWH across the house, 45' from bathrooms, or intentionally place it much closer?
3) Recirc hot water or not, depending on items 1 and 2

Is there a great solution to be able to recirc hot water without it costing a lot? Hoping insulated lines would be the game changer here. I've also read about optical sensors in bathrooms to trigger the recirc pump on demand which seems smart as well, if needed.
Thanks for any input!

GGross

Why not use a boiler with a boiler mate (indirect water heater) so that you can use all 4 baths at the same time if needed, and possibly have a better sized boiler for the space heating? I like the newer Viessmann as they have separate tappings to pipe straight to the water heater, this allows you to avoid a mixing valve for the radiant portion in most applications.

As for the recirc you have the right idea about it. It can be expensive, insulate the lines and reducing the amount of time you recirculate is the best way to make it cheaper. Another benefit of a tank is that you won't get any cold water sandwiching like you could with a combi without recirc, if you want hot water at the ready just do a short recirc time during used hours from your tank to get warm water in the pipes

jimna01

Homeowner speaking here. I have an indirect water DHW storage tank plumbed off my oil fired boiler.  I have a Grundfoss recirculating pump on my DHW. The water storage is about as far away from the kitchen sink as possible. I had Grundfoss pump system with a new PEX return line installed about 3 years ago.  The supply in my house is copper. All the copper is insulated with foam tubing insulation.  My copper plumbing is as old as the house which was built in 1960.   The Grundfoss pump I had installed is an adaptive pump and over the course of the first week it “learns” your usage habits and builds schedules around that. So the pump does not run 24 hours a day .  If it does not detect and usage for 24 hours it goes into vacation mode and does not run again till it detects usage.  I have not noticed any real difference in my oil consumption but have noticed a reduction in water usage by  having open the kitchen faucet for several minutes to get hot water.  My dishwasher works better as well as it has a constant supply of hot water.  

Larry Weingarten

Hi, Just to give some general info, I've been told that running a recirc system 24 hours a day, using uninsulated lines can triple your water heating bill. It will depend on lots of variables, so is only a general statement. For efficiency, demand controlled pumping is much better than any other approach when using trunk and branch plumbing. It has as much as 10% of the heat loss. Manifold plumbing is another approach that can work very well if you don't have really long runs, have decent water pressure and can keep the lines small in diameter. As a demonstration, I just plumbed a new home with 1/4" PEX and in worst case, it takes six seconds to get hot water.

Yours, Larry

hot_rod

The heatloss from the recirc loop is basically flow rate and insulation value.

A recirc loop is really nothing more than a hydronic loop as far a heat loss to the space.

It just turns into an open loop system when you turn on a faucet.

Hot_water_fan

A few things: 

1. It’ll take a huge combi to supply 4 bathrooms (4 showers?!) at once. A tank is a highly performing option and would let you use a more sensibly sized boiler. It could be an indirect or an independent tank, doesn’t matter much. 

2. 45’ isn’t that far. That’s closer to 10 seconds than 120 seconds. 

3. Of course, placing the heater closer solves your issues. 

EdTheHeaterMan

Here are 3 ideas that may help to reduce the cost of energy and wasting water
1. Put an indirect water heater close to the point of use. Not 45 feet away. Then you don't need a recirc system. The plumbing from the boiler to the indirect can be insulated to lower the pickup loss associated with the closed system side.

2. Home runs to the fixtures using the smallest size PEX from the DHW location. ⅜” for Lav and ½” for shower. I just did that in my home using Vega ManaBloc from SupplyHouse.com https://www.supplyhouse.com/Viega-NPTS038-49620PX-24-Port-Polymer-3-8-PEX-Crimp-MANABLOC-Package-NPT-Supply

3. Operate the motor for the recirc pump only when the far away bathroom(s) are in use. I did this in Brigantine NJ when I got tired of waiting for 90 seconds for the Hot Water to charge all the ¾” hot water main and branches until it passed the bathrooms and kitchen. Then take a 35 foot journey to a powder room on the other end of the home. All ¾” pipe until it splits off to the outside shower that is shut off in the winter.

The pump only operated when the powder room light was turned on. After you finish your business the pump had hot water there when you were ready to wash your hands for about 30 seconds. when you leave the room, turn off the light and the pump stops. The hot water cost and electric to run the pump was not even noticeable on the utility bill.

Teemok

If efficiency is a primary concern, I recommend a wired push button type. Taco makes one. It can be done wireless but... you know, wireless. A decent pump is just a few seconds wait and your waste is very small. Some use motion sensors or buttons with a timer.

hot_rod

Grundfos had some new recirc pumps at AHR. The GO ap would be another option for starting the pump remotely without wiring or a shuttle valve below the sink.

retiredguy

Here is what I did. I installed 3/4"X3/4"X1/2" tees as close to the sink/shower as possible and ran 1/2" copper back to the hot water tank. I have 3 full bathrooms so I ran 3- 1/2" copper pipes and manifolded them together near the hot water tank. I removed the tank drain and ran the recirc line to that tank access and reinstalled the tank drain valve. I used the smallest B&G bronze pump I could buy, that is rated at 39 watts of electricity when running. I wired it with a plug end that is plugged into a "plug-in" 24 hour cheap timer that in turn plugs into a receptacle in case an inspector has a problem with me not being a registered electrician. I set the timer to cycle the pump on during the times that we are or should be using hot water. I did this 25 years ago when the house was new and it has served me well. There may be more modern or sophisticated ways to control the pump but it works for me since I don't use apps and stuff. I insulated all hot and cold water lines in my house just because I could.

my 2 cents.

bryantroll

Wow, great discussion and very helpful, thank you!

It sounds like combining an indirect water heater with the boiler may be a good solution -- I will do some more homework there.

I also like the idea of tying the recirc in to the bathroom light switches and/or an optical sensor. I could also tie in to the kitchen sink light, even though I don't turn that on as often as I should (maybe I will now).

The laundry room room will also be far away from the hot water heater but I can include a recirc to the light switch of the laundry closet to remedy that.

bryantroll

Ok, ideas developing but I have a question — is it possible to use a combi boiler in conjunction with a tanked water heater? The combi could raise the water temp to ~100 degrees and send it to the tanked water heater to do the rest of the heating. 

In theory, this would relieve the load from any one component, or am I missing something?

This idea was born out of only finding indirect water heaters sized at 30 and 40 gallons and finding them comparatively expensive to a tanked water heater, if it’s possible for a tanked water heater to fill the same roll. Are there better indirect water heater options I’m not seeing or understanding? 

Considering HE natural gas, or heat pump is an option as well. Heat pump pros are less ducting to outside, cons are up front cost and pulling heat out of the always cool living space in the basement.

hot_rod

Adding a tankless adds more complexity. Power, fuel it, vent it, and descale it
A boiler and indirect would be simpler, less maintenance 

Hot_water_fan

Indirects come in all sizes. A combi really isn’t a good fit for 4 bathrooms. 

Alan (California Radiant) Forbes

I installed a thermosiphon recirc at my house. Lucky that my fixtures were above the water heater; sloped the supply up towards the fixture, the return down towards the water heater. Don’t need a pump. 

Inefficient is not the right word to use for a recirc. In my mind, it’s a convenience. Like the comfort of security cameras around your house, Siri to command your desires to, a Tesla in the driveway….You’ve got to pay to play. 
Just keep it simple. 

Teemok

Simple is good. Efficient as can reasonably be is best. What that is and who decides is up for debate. The water savings that is realized by a recirc. system is shifted to the places the parts were manufactured, materials were refined and extracted. Is there a net savings? I guess there is a savings in one local. The fuel needed to keep an un-insulated hot water pipe system hot all the time vs a well insulated well controlled one is dramatic, as a percentage. But most people don't care much about it because it's chump change to them. It's not worth stigmatizing folks about. If you want peak efficiency I'm glad to help with it, if you don't, so be it. It's not like you've installed an auxiliary diesel injector in your road princess's monster truck exhaust to give the world the bird with a black soot cloud. The cost of fuel will push in the good direction, if much too late. Convenience and comfort drivers are indifferent juggernauts that humanity is, mostly unwittingly, pitted against.

hot_rod

A recirc basically swaps water waste for electric and water heating energy. If you have a lot of uninsulated copper in a cold space, like a crawl space the operating cost of the recir connivence can be quite high.

It's a hydronic heating loop, basically. That may never catch up to the load