Indirect DHW vs tankless

MAQ Crook

I am considering whether to put on an indirect DHW off my peerless boiler or going to a tankless Rinnia. Which would be less cost effictive as far as energy consumption? 

Al Letellier_21

tankless vs. indirect

I fail to see how an indirect  can be more efficient cost wise. A tankless like a Rinnai doesn't store any water, only heats what you use, is fully modulating and can produce literally endless hot water for the average home. An indirect stores a lot of water that has to be continuously reheated when not in use and the boiler may be oversized and costly to run just to manufacture hot water. I have had an indirect off an oil fired boiler for years and am going to a WM Ultra gas boiler and a Rinnai Continuum. We have a small home and only the two of us, so it makes a lot of sense not to store hot water. My boiler is running as I write this, just to warm up the tank....why????

EricAune

Al raises a good point

What are your demands for domestic water?  I am a large proponent of tankless water heaters but consideration of what is in your home (i.e. large soaking tubs, multiple showers etc.) must factor in for the proper selection of which tankless is right for you.



Rinnai and other manufacturers have multiple sizes available to meet the needs of most residential installations, all of which only heat water when needed and that saves money every time. 

TonyS

Like Al and Eric said..Tankless

I removed my oil boiler with a phase 3 indirect over 2 years ago. I replaced it with a tankless unit. There are four of us and two bathrooms and it has no problem running two showers at the same time. The only thing that could be a pain is the wait for hot water when washing your hands at the lavatory. Personally I never wait for hot water after using the bathroom. If that is a concern There are units on the market that maintain a couple quarts of water at temperature just like a regular tank unit, these units also come equipped with a circulator if you choose to run a circulating line to the furthest fixture. These units work well but they do have some heat loss.

CMadatMe

May Not Be The Best Move

While I agree whole with Eric, this in the long term may not be the best overall solution to save on your overall energy cost. If going tankless I'm safe to assume gas is your heating source. I would say the boiler/heating is the source of your energy cost not the domestic. I would be looking at replacing the boiler with a modulating condensing boiler first.



I agree that the tankless is the best way to go for the domestic in this scenrio but  I question whether it is the best investment.



If you plan on staying in the home for some time. I would suggest you have a heat loss of the home done first. Take a look at whether an investment in upgrading the heating system is an overall better investment. My feeling is that your existing boiler is oversized and you may find greater savings in looking at the heating system along with your domesic needs.

TonyS

I think the guy just wants a water heater

Sounds like he is going to replace his standard tank water heater and would like to bump it up a notch by purchasing something better, He ask about a tankless or a indirect!

He didnt say anything about changing his boiler or doing a heat loss or having infrared cameras locate holes in his home. If he would have ask for a good investment, I would tell him to buy silver.

How did you get the "feeling" his boiler is oversized? I read his short simple question 8 times and still havent got that feeling.

ScottMP

indirect

"continuously reheated when not in use ...."

Makes it sound like a huge energy loss. With high desity foam most indirects loose less than 1/2 degree per hour. Over a twelve hour period that would be less than 6 degrees .

I wouldn't call that a poor decision,

I do like tankless but I also like indirects.

Scott

Jean-David Beyer

I am biased in favor of indirect fired water heaters.

And I am not a professional either. My only experienced with a tankless hot water heater was in France in 1950. It was OK to fill a bathtub with, or a large kitchen sink. But useless for washing your hands, or to clean a couple of dishes. You needed quite a flow rate to get it to turn on. And if you set the flow too high, it was not hot enough. I would not be surprised if there have been improvements in those in the last 60 years, and I do not know how old the unit was then.



At the other extreme, I have an indirect now. Weil-McLain Ultra Plus unit made in Belgium, so I do not know who really made it. It looks like Triangle Tube's Smart series. It claims 2" of foam insulation and 1/2 degree/hour temperature loss. It does not say at what water temperature and what environmental temperature this measurement is made. My impression is that the claim could well be true. When I first got it, I spent a lot of time in the garage (where it is) observing the operation of the system, and it is my impression that it only demanded heat about twice a day, and for between 5 and 10 minutes at a time. It may have demanded heat in the middle of the night, but I do not know, and do not think so.