tankless water heater with recirc. pump?
BTC
| Posted in Energy, Heating & Insulation on
We installed a tankless water heater in our remodel to serve two bathrooms. It works great, except for the amount of water wasted out of the tap while the heater is heating. Living in drought country, we’re trying to conserve all we can and this adds up to a lot of water wasted. So I researched recirculating pumps for tankless heaters and came up with one; I think it’s called the D’mand pump. A new possibility: my builder just handed me info on the Navien “Condensing 98%” tankless heater with a built-in recirculating pump and other promising-sounding technological innovations. He says it is brand new. Does anyone know anything about this brand or model? If it works, it will solve our problem handsomely. Thank you!
-BTC
Replies
Someone posted that they have that system and I believe they were happy with it. I am in a similar situation you are in so I saved the link; http://www.gothotwater.com/cart/scripts/prodList.asp?idCategory=18
Can't remember the thread, but it was in the energy heating catagory.
Mike
Small wheel turn by the fire and rod, big wheel turn by the grace of god.
I must be missing something here. I'll admit, I don't know much about tankless water heaters.
If a tankless wtr. htr. only heats the water when on demand, what is it circulating? Is it simply circulating the water in a pipe that loops from the TWH, to the kitchen, bath, etc. back too and through the TWH.
If the TWH is not operating, then it is circulating cold wtr. Does the circulating water in the pipes periodically reach a temperature, cool enough to cause the TWH to think that there is a demand, come on from time to time and heat the water in the circulating lines so you will have access to the small amount of warm water stored in lines until theTHW fires up?
If that is the case, then the so called efficiency of these units would be pretty much defeated, it seem to me. Somebody "please splain it" to me.
I am not by any means an expert. What you are describing is a traditional recirc. pump, which does not really work properly with a tankless system. The one in the link proports to work only when you want hot water by means of a remote control.
I have a tankless boiler that does my radiant and domestic. It was a choice I made and I have had some problems with the system, but we do enjoy being able to have the whole family shower in the evening w/o running out of hot water.
Our gas bill is not out of line with other residences in our area, but I can't compare to our old bills because the house was expanded greatly during our remodel. Mike
Small wheel turn by the fire and rod, big wheel turn by the grace of god.
The recirc system does not respond to tank (or tankless) temperature--it is activated by a sensor that attaches to the recirc line. So, whenever the temp in the recirc line falls below the set point, the recirc pump runs, initiating a flow of water that, in turn, causes the burner to fire, thereby re-heating the water in the recirc loop so that hot water is immediately available at each faucet that branches off the recirc loop.
For energy saving, it is also advisable to install a timer on the recirc system so that the system recircs only at times when occupants are likely to use hot water. And, of course, insulate the entire hot system.
Maybe I didn't state it clearly, but that what I was saying. Also, as I was saying, the addition of a circulating system reduces the claimed efficiency of these units.
I'm still not sold on tankless water heaters. I don't feel that the numbers add up to the claims.
I will continue to show and spec. conventional water heaters with circulating pumps on timers and with aquastats, all properly insulated.
I have heard of recirc systems that only work on demand. In other words you come into the room and tigger them somehow and then they start to recirc. Works the same with both tankless and tanl systems I guess. You don't waste the water but the difference is that the recirc pump isn't running all the time and the water heaters arn't running either trying to heat water you keep running through it constantly.
Looked at another way, the system I am describing works just like turning on the faucet and letting it run to get hot water except the water doesn't go down the drain it just goes back into the system. You would still have to wait for the water to come up to temp but you don't waste the electric and gas as you would with constant recirculation.
Here is one:
http://www.gothotwater.com/D'MAND/how.asp
That is the exactly the system I described in my post. At least I thought I did. I must be slipping. I will go back and check.
The Webb site you referenced showed a water tank (water heater), a circulating pump, a circulating pump timer, and a pipe water temp. sensor (what I termed an aquastat).
On electric water heaters, I also install a timer to turn the water heater on and off. I set the water heater timer to come on approx. an hour prior to the time set for the circulating pump and the time normally expected need for hot water.
Anyway, the very ordinal post had to do with circulating systems and tankless water heaters.
Sorry if I misunderstood your point.
I have serious reservations about tankless WH's in most situations, too.
Many homeowners are misled by the term "instantaneous water heater"--they think it means instant delivery at the hot faucet, which they would only get if they install the recirc system. And that hurts the efficiency rating as you noted.
Also, the efficiencies and payback claims by the tankless people often do not factor in all the installation costs on a a retro-fit, which can be considerable. (Increased gas pipe size; special flue; water softener; electric service, etc.)
Your point is well taken. I have ask two or three plumbers I know and they love them. It puts big bucks in there pockets. They tried to convince me that they were greatest thing since sliced bread. I guess I can't blame them. It's the American way.
I don't have any first hand knowledge or know this for a fact, but I've heard that they have had maintenance problems and they sound like a jet engine when they fire up. I have seen them installed but I've never seen one in operation. I would like to know. I can see where there might be unique situation where a TWH could be a possible solution.
I am a general and was on a job where the plumber, a reputable guy, worked directly with the owner. She wanted a tankless system and a recirculation pump. He installed the system and included a seperate storage tank. He said the tank was necessary to make the recirc feature work. I said but you are adding .... a tank! He just shrugged.
You do not need a separate storage tank to make a recirculating system work on a tankless. That said, it may be a good idea to have a small storage tank upstream from the tankless.
Seems like the most important thing to remember for a recirculating system is that you are turning the downstream pipe from the water heater to the faucet into a mini hot water storage tank, so the lines need to be insulated as best they can.
Found it; 114216.13
Mike
Small wheel turn by the fire and rod, big wheel turn by the grace of god.
BTC,
From the literature it looks like the Navian system is a tankless water heater with a built-in on-demand recirculation pump like (like the metlund pump).
Personally, I've been using a Takagi tankless system for 3.5 baths for just over a year and it's been great. But at some point I'd also like to install a Metlund recirc system so I don't have have wait for 90+ seconds of water to go down the drain for hot water in the kitchen. The kitchen is in a location that needed extra runs of pipe to bypass structural beams and hence the 90+ second wait for hot water.