indirect v.s. on demand

rick in Alaska

I have a customer that is getting a new gas boiler and wants to upgrade her electric water heater to either an on demand or an indirect. The existing boiler piping has a manifold that is set up with a spot to tie in the indirect if we go that way.

The problem is whether it is better to go with the indirect or the on demand. The issues are that the boiler runs in the summer to heat the domestic with the indirect and I am concerned that having the residual heat in the boiler is not as efficient as having the water heated directly with the on demand. Think heat loss from the boiler that is now heating a space that needs no heat.

 On the other hand, the indirect heats water a lot faster, and I believe more efficiently.

The indirect has a lifetime warranty and virtually no maintenance, and the on demand is I believe 10 years and a lot of parts to go wrong.

I believe the on demand is the way to go for efficiency, but I wonder how much it costs in the long run, say over 10 years or so.

Either one will supply their hot water needs fine, cost about the same to install, and are just as easy to install in the space available.

Any thoughts on which way to go are very much appreciated.

Thanks, Rick

VictoriaEnergy

IMHO

I find smaller houses with few occupants tend to be happy with on-demand units. 



Bigger houses and families tend to expect and need more than one use of hot water at the same time, so in-directs are the best for that situation.



On-demand units are the most energy efficient, but no one in a working family with 3 teens will care about that at 7:00 AM. 



(from a guy with 3 teens)

icesailor

On Demand Flow:

And the starting and stopping of the On Demand plus the temperature fluctuations will drive the customer to distraction until you put in a buffer tank. Even on a small single family home. Put in the indirect. Or use the On Demand but be sure to put in the buffer tank.

IMO and experience.

Joe Mattiello

on demand

I like the buffer tank idea.  I too have an on demand Rinnai heater that I'm very happy with, but I believe more water is wasted waiting for the heat exchanger in the unit to begin providing hot water.  The buffer thank provides the reservoir to draw from minimizing the startups on the heater. 

Jetfan1

on demand

I have installed both, and replaced many indirect units with on demand units. Being able to look through customers histoy, the decrease in oil usage, and the new propane usage, it is evident that the customer saves much money with the on demand, in my area(very northern ny) the units will pay for themselves in a few years. The issue with 3 kids doesn't come into play if the units are sized properly.

rick in Alaska

cost comparison

Thanks for the replies so far.

Does anyone have any real life numbers on what the different scenarios would cost on a long term basis? I am wondering if I went with the indirect, I would have to run the boiler and deal with the standby loss in the summer, but I would have no real maintenance issues with it.

 If I went with the on demand, I would have to worry about maintenance issues along with the cost of adding in a buffer tank setup. I also worry about longevity costs.

 I personally like using the Rinnai's for making boat loads of hot water, but your concerns about hot water lag times are something to consider.

I am one of those people who want to make the best choice for my customers rather than sell them more expensive equipment they don't really need, and unfortunately, I am still not sure which way to go.

Thanks for the ongoing advice.

Rick

Gordy

Boiler efficiency

Your customer has a new boiler what efficiency? If it were a mod/con it would be more efficient even though it would run at a higher temp during hot water production verses a ci boiler in the mid 80's eff.





Wasting water for hx delay is a concern people need to consider, and build in a buffer tank with on demand as joe did.

rick in Alaska

boiler efficiency

Thanks for all the replies.

 The boiler we decided to got with is the Weil Mclain gv3 90+. A regular GV would probably be just as good, but price is same at this time, so that is what we are going with. We are going from a boiler that is capable of putting out 140k btu to one around 70. The heat loss came in at 54k after energy upgrades.

The heating system is a suspended tube setup, two zones. Since this setup will only condense for a very short time, I felt like the modcon was overkill for this setup and not worth the potential problems down the road with longevity and maintenance. In this case, with this heating setup, simpler is better. 

 I will have to look in to the costs associated with setting up an indirect with the buffer tank.

 Thanks, Rick

chapchap70

Low energy use for hot water

I have a friend that had a oil fired System 2000 with the brazed plate heat exchanger and storage tank setup installed last year.  He told me he got an oil delivery about May 15th and recently switched oil companies.  His new company topped off his tank about August 15th and the delivery amount.....     5.6 gallons.



It is just him and his wife there but there is little energy wasted for hot water without the concerns of cold sandwiches.  If the electric water heater is in good shape, it can be used as the storage tank.

Harvey Ramer

You are comparing apples and oranges.

You have to remember that the majority of hot water usage only occurs at a flow rate of approximately 2 gpm. So using an on-demand that is capable of producing 8 gpm at a 70deg delta-t is like using a 200 HP tractor on a 1 bottom plow. On the other hand, if it is a vacation home or they have one of those showers with a bunch of shower heads, on demands are just the ticket.



And the storal of the mory is, look at the customers needs and figure out what will best suit their situation.