Indirect water system? Can you help me understand it?

Mark_46

Homeowner here...but

Indirect water heaters are far superior 1) The recovery times are quicker 2) they are far more efficient. Their efficincey is tied to the the boiler that heats it and better construction of the tank (less stand-by loss) 3) they are capable of delivering 'gobs' more hot water (first-hour draw capacity). 4) Indirects also have a longer life expectancy by default. Less disparate temperatures throughout the design.

Down side...more cotstly to purchase and install.

Otherwise, your heading in the right direction switching to an indirect.

Adam_24

Hi,

We have had an installation person recommend an indirect water system for our new steam system installation. What has been suggested to us is to leave off the tankless water heater on the boiler, saving us $300. and add a new stainless steel water heater that would cost $1600. but would have a life time warranty.

Here is my understanding of how that works...

The hot water tank is filled with cold water from the house water supply line, then there is a coil in side of the hot water tank in which hot water from the boiler circulates through this coil and heats the water in the tank. Is that right?

That doesn't really sound very functional to me for some reason. I am picturing a large 50 gallon tank full of cold water with a coil at the bottom circulating hot water. If that is the set up, I can't imagine how long it would take to warm all the cold water in the tank. Maybe the person explaining it to me, was unclear and I have it wrong?

If the coil is actually circulating hot water from the boiler, then doesn't the system still have to run quite awhile and keep turning on to get the water hot and keep the water hot? So how am I saving wear and tear on the boiler, or saving the system from coming on too often in the summer, with this system?

Also, I wondered about whether it is worth the cost of the stainless steel tank. I never believe a 'lifetime' warranty is worth much. What do you think? Have any of you had experience with installing this type of hot water system for a steam system for your customers?

Thanks ... :-)

maryrenov8s

storage tank vs. tankless

I'll be eagerly awaiting responses to your question. I am a remodeling contractor in S.C. and am planning to install a similar system in my personal residence. Such systems are rarely installed anymore in this area and I am having difficulty even finding anyone to discuss the system design with!

I would also like opinions on these three options for providing hot water for hydronic (radiator) heat and potable hot water:
- boiler with tankless - or -
- boiler with indirect storage tank - or-
- boiler with indirect storage tank AND tankless
(Boiler and tankless would be NG-fired.)

Which system is cheapest to install?
Which system is cheapest/most efficient to operate?
I don't have a heat-calc completed yet, but have 70,000btu as a guess-timate.

MGH

Weezbo

the occupantcy level or bedrooms is how you would

determine what size indirect to use for Domestic hot water..useage ,like 20 man bath tub or indor olympic wave generator things like that also tend to be meaning -full *~/:)

SVDW

Indirect

I have a 40 gallon Burnham indirect running off my 125K/BTU Utica USC boiler. The recovery on these setups is far better than a standard water heater B/C I have 3X the BTU's heating the water. Typical water heater will have around 40K/BTU heating the water so a boiler will create more hot water faster. I have never been able to run my indirect out of hot water even when the relatives are over for a weekend. There's no way the storage would satisfy that demand so the thing was keeping up with the demand mainly on recovery. The other advantage is my stainless indirect needs no anode rod so I have no maintenance other than flushing the bottom of the tank now & then. The long term efficiency should be better as well b/c eventual sediment deposits caked on the bottom of the tank will not cut down on heat tranfer. In a water heater these deposits can build up & it's like trying to heat a pan of water sitting on a brick. I also like the fact I only have 1 burner assembly to maintain instead of 2. My boiler does run a little during the summer but I don't worry about start-up in the fall either. If it sits idle all summer pumps can set up & contacts can get rusty possibly giving you problems the first time you need heat in the fall. I've compared my gas bills BF & after the install & they actually went down. I also had 1 venting assembly so install was a little nicer/cheaper instead of running another flue outside. As far as longevity IMHO boilers & indirects should last at least twice the life of a typical water heater. I think if you factor in the cost of changing out the anodes & replacing the heater in 7-10 years the indirect is well worth the money. I work for a plumbing/htg wholesaler & after looking at all the options I went with an indirect. Sorry this sounds like a sales pitch but I am really happy with my indirect! Good luck on your project.

Adam_24

Yes, demand is important..

Hi Weezbo..

Yes, our demand at our house would be 5 adults all taking showers, doing laundry, a dishwasher, and that is about it. Nothing fancy. :-)

Adam_24

Thanks SPV

Hi,

Thanks for your detailed and thoughtful response. NO I didn't take it as a sales pitch. I am interested in this system, but your explanation was a little techincal for me. I don't know how my situation compares to yours. We have oil not gas, we would be installing a WM Gold boiler with a Carlin burner and not sure what BTUs we would have etc etc...

But I guess what I get out of it is you are happy with your system. So we should keep asking questions and considering it.

Adam_24

It is sounding good to me. I usually don't mind a little bit higher up front cost if a system really will deliver as promised and in the long run really will save us money.

They have been claiming our burner/boiler will run less and come on less frequently than with the tankless heater, and I am not hearing that from anyone responding yet.

thanks :-)

LarryC

Less run time

They have been claiming our burner/boiler will run less and come on less frequently than with the tankless heater, and I am not hearing that from anyone responding yet.

Home owner here. The story with the less runtime is this.

A tankless coil will cause the furnace to cycle more often to keep the water in the tankless coil hot. Whether you use hot water or not. Also the volume of water in the tankless is small. If you use a gallon of hot water to wash your hands, it will cycle the furnace. Heated air is always leaving the furnace and going up the chimney, the coil will cool off, and cause the furnace to cycle. All of this cycling will cause the furnace to use fuel all day long.

An indirect tank is MUCH better insulated that the conventional oil or gas fired water heater. So once the tank gets up to temperature, the water heater may not call for heat for the rest of the day. Taking one or two gallons out will not trigger another firing cycle. Not being connected to a chimney removes another heat loss.

It will cause the furnace to come on during the summer, but when it does run, the furnace runs for a good long time to fully recover and then turns off for the rest of the day.
As these heating professionals will tell you, running for a longer period infrequently is better for your furnace and more efficient, than running for a short time more often.
Just like city vs. highway driving for a car.

Larry C

SVDW

indirect

Sorry I got a little technical on you but maybe this will help. Regardless if you use oil or natural gas you will still benefit from an indirect. You have 1 less burner to maintain, filter to change, ect. so there will be decreased service cost. You might want to get a cost on an oil-burning water heater to compare as well. They are typically more expensive than a gas unit b/c there is a smaller demand & it's got more parts. I think we sell 1000 gas units to 1 oil burner in my area. They also cost 2-3 times more. May be different where you live. I do think getting rid of an extra burner is worthwhile. My dad had an oil burner water heater & they do require regular maintenance. Hope this helps.

Adam_24

Nice clear explanation Larry. It sounds like it makes a lot of sense. One point I am still not clear on. When you say 'oil or gas fired tank', you aren't meaning the tank itself has a heat source, you just mean the tankless is making the hot water with the oil/gas from the boiler, right?

Love the comparison to driving in city/highway conditions.

Thanks a lot

Joe Brix

Don't forget

Most steam boilers have a triple aquastat, so the burner will still fire several times a day to keep the boiler up to a min temp. But even with an indirect, you should save cycles as small Hot water draws won't trigger the boiler to come up to min temp as frequently.

Paul Pollets

Make sure...

that the indirect water tank is rated for steam. To my knowledge, only the Viessmann V300 tanks are fully rated for steam supply to the coils. BTW, they cost more than $1600.00

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

LarryC

'oil or gas fired tank'

What I am refering to is a stand alone unit that is made up of a oil or gas fueled burner, which is used to heat the water in the storage tank. They typically consist of a water tank shaped like a vertical cylinder with a hole in the center. The hot exhaust from the fuel burner goes thru this hole and heats the tank. They are usually big and heavy without alot of insulation on the outside surface of the tank.

As other people have pointed out, you now have another burner which needs maintenance, another burner that also needs a chimney or an exhaust, another burner that needs combustion air, AND to top it all off, it also functions as a room heater! (which you probably don't really need)

Again, I am not a heating or plumbing professional, but from what I have seen and learned, an indirect domestic water heater makes great sense if you are installing a properly sized steam boiler or warm water heating plant.

To repeat the question that these folks ask all the time, "Have you had a heat calculation done yet?"

Larry C

Scott04

An indirect heater will give you around 180 gallons of hot water the first hour (40 gallon tank). It depends on the BTU input, but the point is, you don't run out of hot water. Steam boilers do NOT maintain temperature, unless a tankless coil is installed. With an indirect, the boiler will run when it gets a call for heat (from the thermostat) or a call for heat from the indirect. On a call for heat from the thermostat, the boiler will run off the pressure switch. On a call from the indirect, the boiler will run off an aquastat that will limit the boiler temp to around 180*. (This prevents generating heat in the summer)

Pretty much any indirect can be hooked to a steam boiler as it is hooked as a hot water loop with supply and return pipes below the water line.

With a tankless coil, the boiler maintains temp. all the time. During the off cycle air flows through the boiler and up the chimney taking the heat from the boiler with it. This causes the boiler to cycle frequently. With an indirect, the boiler still cools down from the air, but it doesn't fire again until there is another call for heat.

As to how long it takes to heat the tank of cold water, which would only happen at the initial startup, or if the boiler or indirect are turned off for a long time, if the boiler is up to temp. it takes around 20 minutes or so to heat the tank to 120*.

The bottom line is that the indirect is the most efficient way to heat your water. It saves wear and tear on the boiler, and saves fuel as well. With the initial cost, the payback takes longer, but it will pay for itself well before it needs to be replaced.

If you want to know more about how the indirect hooks to the steam boiler go to the very top of the page and click on Heating Q&A. From there, click on Condensate Hot Water Heating. This deals with adding hot water heat to a steam system, but if you scroll to almost the end, he shows you that an indirect can be hooked in the same manner.

I hope this helps,

Scott

Adam_24

It helps a lot Scott, thanks for the clarification and for the directions to the FAQ. I haven't been there yet, but glad to know it is there.

TLynch

I have a Weil-McLain Gold steam boiler w/ 40 gallon WM Gold indirect, and I'll also vouch for what a great system it is. Plenty of hot water, cycling/recovery time seems minimal, and I think it's a good thing that the boiler runs year round. When heating season arrives, just turn up the thermostat -- no worries.
Tim