# Does anybody use an indirect water heater?



## EatenByLimestone (Jul 12, 2010)

I've read a little and spoken to a few people.  They appear to be pretty efficient and one person said they have a long life.  Does anybody have any experience with them?

Matt


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## btuser (Jul 12, 2010)

Very long life. Seasonal efficiency is dodgey.  There's essentially no loss during the heating season, but Summertime is a different story.  
Even with a 3 pass well-insulated boiler you're going to get heat loss.   I've figured mine to about  1200-1500btu/hr heat loss during regular usage here in July, so if you figure 24hrs @ around 30k heat loss, I'm losing about 30-40% efficiency during the Summer months to heat loss for hot water.  I heat with oil.  My boiler is well-insulated and I have flowchecks to stop gravity flow on both return and supply.  The boiler header/near piping is not insulated right now, but I don't feel that's where the heat loss is coming from.  Its the 22 gallons + 500lbs of steel that needs to be heated up whenever someone calls for even a small amount of hot water.  Something's up with my auquastat.

I'm currently trying to "dial in" my indirect, so I get longer times in between firing. Originally, my auqastat sensor was all the way at the bottom of the tank, and I think by raising it to mid level I may be able to eliminate some of the nuisance firings I'm experiencing.  My boiler is cold-start, but I never see it go below 140 degrees because of a call for heat.  I have a mixing valve and maintain tank temperature around 140 degrees, but because the auquastat bulb is pushed to the bottom of the tank, I think the aquastat is interpeting the inrush of cold water as a need to recharge.  I'm slowly raising it about 2"/day to see if I can get the boiler to stop firing so often and yet not run out of hot water.  If you heat with wood and have storage then you've pretty much already have an indirect, just need a coil.

Long answer short:  Very efficient during the Winter, and if you have a tub/large draw at once it is a great option for a lot of hot water all at once.  Summer months are really going to depend on whether you have gas and can modulate a low-mass system, or whether you have oil which is only one speed.


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## EatenByLimestone (Jul 13, 2010)

At the moment, I heat with oil also.  Long term plan is to switch to switch over to gas, but my boiler was installed in 12/07.  I've been told gas conversion kits are high 70s/low 80s in efficiency.  Since my boiler was sized too large I think it would be better to replace the whole thing when my oil tank goes.   The tank is pretty old and the legs are just starting to split.  

At current oil prices, it looks like the heat loss would be about a dollar a day.  

You pointed out something I didn't think of with the smaller tanks.  Their rated capacity looks like they would fit my needs, but I didn't stop to think about having to heat up the entire heating jacket each time I needed hot water.  Nuisance firings never crossed my mind.  I was looking at the higher capacity tanks due to the input BTUs listed.  They were listing 100K btus and while the current large boiler gives that off, I was thinking the new boiler would be something around 60K btus.  It should take longer to heat the volume of water with the smaller unit decreasing the amount of water that can be delivered in an hour at a set temp.  Increasing volume seemed the only way to get around this.  The larger volume may help absorb the cold and decrease nuisance firings also.  I never thought of a tub either.  I used showers for my calculations, but with a little one that will be taking baths a tub will be used pretty heavily.

Has raising the bulb helped?  Are you seeing less firings?  

Matt


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## btuser (Jul 13, 2010)

I came up with the idea about two days ago.  The top of the tank ( I have a digital thermometer) is about 140 degrees and is mixed down to about 130 before leaving for the faucet/shower.  Its for this reason I can not figure why the tank fires on 1/2 gallon draw for someone washing their hands.  I'm guessing the stratification of the tank is still happening at the bottom of the tank, so if i raise the probe I can increase the length between firings.

Also at the same time (not good to try two things at once when troubleshooting) I'm trying to raise the delta on the boiler loop.  Currently with no restriction I've got about 3-5 degree difference between supply and return.  I'm throttling back to try and increase the differential in hopes that the boiler will heat faster and shut off, and then with the indirect still calling for heat it will act as a post-purge function.    

I'm also looking for a 100 gallon dual coil indirect so I can do a solar project......


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## hemlock (Jul 13, 2010)

Hello,
I have indirect oil, and hate it.  It may just be my system, but it strikes me as very inefficient - so much so that I have replaced it with a Marathon DHW heater.  The indirect oil was costing roughly $100-125(CDN) per month for DHW alone.  The burner seemed to be running all the time, for a long time.  I can't see the efficiency of heating water to heat more water.  There seems to be too much heat loss.  Installed a wood stove for heat, the Marathon for DHW, and the home energy bill was slashed by at least 1/2, if not more (had hot water heat, also).  Just my 2 cents....


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## jharkin (Jul 13, 2010)

We have an indirect running on our gas fired steam system.

The boiler is an 3 year old gas fired Burnham Independence (83% - about as good as it gets on steam). Its hooked up to a 40 gallon Superstore Ultra. I have all the steam lines heavily insulated but haven't yet gotten around to insulating the short loop to the tank.

There are 2 of us and our summer time gas usage is around 25 therms/month for the hot water. The one annoying thing is that we do run out of hotwater if you take back to back showers. Either the recovery rating on the tank is really optimistic or the circulator is starting to crud up from the corrosive steam boiler water - haven't had time to try and sort it out ...

As always you will probably get more advice thn you can use if you post this question on the wall over at heatinghelp....


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## btuser (Jul 14, 2010)

When you say back to back showers, do you mean two people in two different bathrooms simulantously?  Do you still have the lag in the Winter, when the boiler is hot?


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## EatenByLimestone (Jul 14, 2010)

jharkin said:
			
		

> We have an indirect running on our gas fired steam system.
> 
> The boiler is an 3 year old gas fired Burnham Independence (83% - about as good as it gets on steam). Its hooked up to a 40 gallon Superstore Ultra. I have all the steam lines heavily insulated but haven't yet gotten around to insulating the short loop to the tank.
> 
> ...



How big is your boiler?

Matt


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## jharkin (Jul 14, 2010)

btuser said:
			
		

> When you say back to back showers, do you mean two people in two different bathrooms simulantously?  Do you still have the lag in the Winter, when the boiler is hot?





			
				EatenByLimestone said:
			
		

> How big is your boiler?



Multiple bathrooms? I could only dream.... very small house. 1 bath. If you take 2 long shows in a row, then #3 will get cold water.

The boiler is a Burnham IN5.  Rating is 140k input, 116k gross, 86k net (358ft2 EDR) for steam.  We only have about 260 ft2 EDR of steam radiation so the boiler is ~ 40% oversized.  Surprisingly it doesn't short cycle.

The problem I am almost certain is the circulator.  The boiler has more than enough excess capacity to heat it even when the heat is on, and according to the Superstor spec sheet  at 180F input it should recover fast enough to make continuous hot water even if I leave 1 tap wide open. In the summer when the tank cycles the burner only fires for a little over 5 minutes before it hits the 180F cutoff,  then the circ runs for 20miin or so to satisfy the tank.

Steam boiler water gets very acidic and tends to carry some rust in suspension. For that reason the steam experts recommend that you use an oil lubricated bronze circulator for indirects or hot water loops rather than the typical wet rotot iron circ that works just fine in closed loop hot water.

Now of course, my boiler was put in by a previous owner using the gas companies lowest bid contractor who probably knew nothing about steam. In fact I wonder how much they knew about reading as the missed some things clearly called out in the Burnham install guide. The boiler was 40% oversized, they forgot to install the boiler side aquastat, and they used a wet rotor iron circulator. Not to mention they stripped all the pipe insulation and didnt replace it and left the pressuretrol set 5x too high...


 I actually have the replacement pump, just haven't got around to changing it out.... The bronze monster is heavy and I have to rig up some pipe supports to take the weight.

-Jeremy


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## jimmie ray (Jul 14, 2010)

I'd say the most beneficial things about an indirect water heater is not having a second burner to service, nor any venting and the associated standby losses from it. The efficiency you get is mostly dictated by the boiler it's connected to - a modulating/condensing boiler is the most suitable application. Priority control may be necessary on some applications, especially if the tank or boiler are not oversized for the demands. I don't know if the poor efficiencies and system complications of connecting to a steam boiler make it a good combination. I did have the Superstore with a stainless tank / cupronickel coil that held up for 15 years, but am now trying another brand with a steel tank and coil that is coated (with some sort of enamel?). The cost of a new S.S. tank dictated that decision, but so far it is performing very well.


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## jharkin (Jul 14, 2010)

Jimmie you made some great points.

Run off a 95% plus mod-con I'm willing to bet a well insulated indirect heater is almost as efficient as a separate tankless, plus cheaper to install and maintain. And the hot water is instantaneous....

In my case, while I am probably slightly more efficient than a standalone gas tank unit I definitely could save gas by switching to a tankless - but at the current gas rates the cost of install would take a LONG time to offset in fuel savings.  Whats it cost to install a tankless? $1500 or more?  I'd be suprised if it cut my gas bill more than $5 or $10 a month.

 Im sure that's what the previous owners were thinking when they put in the indirect. And I doubt I would have done different...


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## btuser (Jul 15, 2010)

That would depend on your boiler.  A 3 pass would be better, as would a pressure-fired boiler like a scotch-marine, but if you have a natural draft boiler then an indirect is not that efficienct unless it is a really, really low mass like the Burnham LE or System 2000 with post-purge.  10 gallon Buderus is about 15k btu in standby.  That indirect is going to fire a couple times a day because of load.   Great in the Winter, not great in the Summer.

The efficiency of the SYSTEM is really what counts.   I bet if a tankless could support the hot water load for the home it would be just as efficient compared to the x-tra cost of the tank and zone for the indirect.  But if you need a lot of hot water and you have oil heat, an indirect is about as good as it gets.  

Solar is a great off-set for an oil-fired boiler in the Summer.  Some day I'll find that perfect 100 gallon dual coil tank, then I'll slap some cheap Chinese panels up on the roof and be golden.


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## jimmie ray (Jul 15, 2010)

jharkin said:
			
		

> Jimmie you made some great points.
> 
> Run off a 95% plus mod-con I'm willing to bet a well insulated indirect heater is almost as efficient as a separate tankless, plus cheaper to install and maintain. And the hot water is instantaneous....



Mod-con boilers actually do not condense the flue gasses at inlet water temperatures much above 130* F, but they are still quite efficient at higher water temperatures. Some integral controls allow different setpoints for space vs. domestic water, since the indirect's heat exchanger needs to have a high (180* F typ.) inlet water to perform to specs. You would still get some modulation of the input, once this setpoint is achieved. If you had radiant space heat, or more radiation in each room than normal, you could run the boiler for space heating more steady, at lower inputs and at lower water temperatures, for the best efficiency. They condense like crazy at water inlet temperatures below 100* F, theoretically squeezing almost every drop of energy out of the burnt gas.


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## Seasoned Oak (Jul 18, 2010)

btuser said:
			
		

> Very long life. Seasonal efficiency is dodgey.  There's essentially no loss during the heating season, but Summertime is a different story.
> Even with a 3 pass well-insulated boiler you're going to get heat loss.   I've figured mine to about  1200-1500btu/hr heat loss during regular usage here in July, so if you figure 24hrs @ around 30k heat loss, I'm losing about 30-40% efficiency during the Summer months to heat loss for hot water.  I heat with oil.  My boiler is well-insulated and I have flowchecks to stop gravity flow on both return and supply.  The boiler header/near piping is not insulated right now, but I don't feel that's where the heat loss is coming from.  Its the 22 gallons + 500lbs of steel that needs to be heated up whenever someone calls for even a small amount of hot water.  Something's up with my auquastat.
> 
> I'm currently trying to "dial in" my indirect, so I get longer times in between firing. Originally, my auqastat sensor was all the way at the bottom of the tank, and I think by raising it to mid level I may be able to eliminate some of the nuisance firings I'm experiencing.  My boiler is cold-start, but I never see it go below 140 degrees because of a call for heat.  I have a mixing valve and maintain tank temperature around 140 degrees, but because the auquastat bulb is pushed to the bottom of the tank, I think the aquastat is interpeting the inrush of cold water as a need to recharge.  I'm slowly raising it about 2"/day to see if I can get the boiler to stop firing so often and yet not run out of hot water.  If you heat with wood and have storage then you've pretty much already have an indirect, just need a coil.
> ...




SO why dont you bypass the ID -WH in the summer and just let the oil furnace heat heat the water,never saw an oil furnace that did not also have a domestic coil in it.


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## btuser (Jul 18, 2010)

> SO why dont you bypass the ID -WH in the summer and just let the oil furnace heat heat the water,never saw an oil furnace that did not also have a domestic coil in it.



Lots of boilers don't have a coil.  None of the 3-pass have them and most if not all of the new designs don't have coils because it would screw up the flue passage.  A coil requires the boiler to stay hot all the time, which in the case of a large mass oil boiler is beneficial because it keeps the stack temp high during short firings.  I'm thinking of adding a second large indirect with double coil that will function as both a solar pre-heater and a post purge after the primary indirect fires.   A worry I would have is a large mass of water maintaining a 100-110 degree temp for an extended period, only to be pushed through a  second indirect for a limited time @140 degrees.  Not a problem during the Summer, when I feel I'd have enough sun to push the temp in the tank past the danger zone, but the Winter may be dodgey.


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## mayhem (Jul 19, 2010)

I hate my indirect water heater.  Very inefficient.  I'm guessing I've got someosort of problem thats been present since new though and just have enver been able to track it down.  Wash your hands with warm water in my house and you're gonna kick the boiler on for 10 minutes because that little bit of hot water out of the tank will trip the thermostat.  

Hot water storage is also a lousy way to go IMHO.  My boiler cycles minimum of 5x a day with no hot water usage, just to maintain the tank.  

It costs me the same amount of oil to wash my hands as it does to take a shower or to fill the tub, despite using probably 1/100th the amount of water.  Before I figured out the pattern when the house was new, we were using about 500 gallons of oil in the warm months (ie: non heating season), now that we wash our hands and most of our clothes in cold water we're down to a more livable 200 gallons or less.

If I could easily swap it out myself for solar or even electric I'd do it.


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## Seasoned Oak (Jul 19, 2010)

I use a coal stoker in winter but when i dont need home heat anymore i shut it down and switch to a small electric water heater.
TO run the Stoker 24/7 just for an occasional hot water use seems wasteful to me.  I keep my hot water heater turned down to the point where you dont need to add cold when taking a shower, all hot is just right ,my electric bill barely moves up in summer so im not using much power. If i were you i would try something similar. My 30 Gal electric was $220 and its a snap to install yourself. No way would i let an entire furnace heat up from cold to in turn heat another large body of water, every time you need a little hot water, I could probably get away with a 20 Gallon electric and i have a family of 5.


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## btuser (Jul 19, 2010)

mayhem said:
			
		

> I hate my indirect water heater.  Very inefficient.  I'm guessing I've got someosort of problem thats been present since new though and just have enver been able to track it down.  Wash your hands with warm water in my house and you're gonna kick the boiler on for 10 minutes because that little bit of hot water out of the tank will trip the thermostat.
> 
> Hot water storage is also a lousy way to go IMHO.  My boiler cycles minimum of 5x a day with no hot water usage, just to maintain the tank.
> 
> ...



Have you figured your usage?  Number of people?  I've got 6 people and from May to October we use about 200 gallons.  

What brand/size boiler and indirect do you have?  My boiler probably fires 4-5 times a day for hot water during the Summer, but I'm not burning much more than 1.25 gallons/day.


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## mayhem (Jul 20, 2010)

I have a Weil-Mclain 3 chamber boiler, rated at 180k btu and the energy star sticker says 86%, system is filled with noburst glycol for the heat transfer fluid and I'm fairly confident that needs to be changed as it was new with the house (installed in late 2002).  Not sure of the brand water heater.  I've turned the H2O thermostat on the tank down to the minimum and whiole it made an impact, its a point of diminishing return and, in my opinion, just a band aid over the high usage and not actually correcting the problem.

We're talking 3 people, I shower every morning, wife and 7 year old daughter shower more or less every other day.  A load of dishes once a day on average, clothes are almost always done in cold water.  Boiler cycles twice for my one shower.  You have probably double the hot water usage I do and you're using about the same or less oil.  

My well is on the silty side so I'm sure I probably need to shut the system down and drain the tank and all the silt, but its been like this since the day we moved in.


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## btuser (Jul 21, 2010)

When you say 3 chamber I assume you mean a 3 pass boiler and not a 3 section.  Weil Mclain Ultra UO-5, with a beckett burner?  Do you know what your hi-limit and differential are set for on the boiler?  If its a cold-start its probably fixed at 20.  The real tell-tale sign is how long your boiler fires while you're trying to make hot water.    I put an hour meter on my oil burner and logged the time for a Summer to come up with my numbers.


How big is your house?  180k is an ultra-huge boiler, but that's a pretty new design so I'd expect it to be better than that.  If you're using twice my oil with 1/2 the showers something's wronger than wrong.  Have you had a real combustion test with analyzer done, or just an eyeball test?


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## jimmie ray (Jul 21, 2010)

mayhem said:
			
		

> system is filled with noburst glycol for the heat transfer fluid and I'm fairly confident that needs to be changed as it was new with the house (installed in late 2002).  Not sure of the brand water heater.  I've turned the H2O thermostat on the tank down to the minimum and whiole it made an impact, its a point of diminishing return and, in my opinion, just a band aid over the high usage and not actually correcting the problem.



Glycol does not transfer heat as well as water, and can particularly be a problem if it is a strong concentration. Maybe your water heater has a double wall coil, to protect against contamination - this would also reduce the efficiency and hourly rating. Setting your aquastat on the tank very low will save oil, but again reduces the rating and there is a chance of bacteria formation (Legonaire's disease). Hope this helps...


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## btuser (Jul 21, 2010)

I've got a mixing valve on my tank so the aquastat kicks at 140 degrees with a 7 degree differential.  The anti-scald valve holds the outgoing temp @ 125 so it makes the 40 gallon tank function as a 50 gallon.   I'm thinking about junking the factory differential and installing a 20 degree diff to increase times between firing.

I thought about the glycol as well, but with such a high-firing boiler I doubt it's lack of btus that is keeping his indirect from fuctioning.  I'd be curious to see how it's firing.


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## SmokeyTheBear (Jul 22, 2010)

He might need to flush his system sediment buildup can cause problems on both sides of an indirect water heating system.


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## jimmie ray (Jul 22, 2010)

btuser said:
			
		

> I thought about the glycol as well, but with such a high-firing boiler I doubt it's lack of btus that is keeping his indirect from fuctioning.  I'd be curious to see how it's firing.



A full combustion test is not a bad idea, if his company's technician carries a kit with more than a smoke gun... I'd be curious if the flue temp is way higher than normal, due to the poor heat exchange from glycol being used. The exact firing rate, CO2, and water temps would be critical for this test, however. Even if the real boiler output to the water heater is somewhat diminished, I'd suspect it's the useful heat exchange area of the indirect that is his problem - there might be three things working against this job: Glycol on one side, and possibly sediment on the other, would reduce the heat transfer ability. If a double wall coil is used, the unit would be specified with a much lower hourly rating for that model - I'd check the model number and see if this design is necessary for non-toxic glycol in that state.


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## stacyalmando (Aug 2, 2010)

When you heat water, a little bit of heat is lost and wasted. When that water flows into another tank of water to heat it, more energy leaks out and is wasted. This makes indirect heating less efficient than directly heating water. this means it is only practical in certain situations.


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## btuser (Aug 2, 2010)

You're not losing the heat when it flows into another tank.  That's how indirect tanks work in the first place, by moving heat through a heat exchanger.  70-90% of the standby losses come from a.) the boiler and near boiler piping.   b.) When someone turns on the hot water and re-heats the piping to the emitter, generating a loss as that water returns to ambient temp.  My indirect loses about 1/2 degree per hour, which comes out to about 170 btu/hr, which is squat.  My boiler loses about 500-700 btu/hr, and that's considered really, really good for a high mass system.  It still cuts down my system efficiency from around 90% to a more sobering 60-70%, so for the Summer months a tankless would win-if I had nat gas.   For the 4 months/year when my outdoor temp is above my ambient temp this is a waste, otherwise it goes into heating my house and I'm figuring about 80% for hot water.

Tankless heaters are better than a standard, open flue gas water heater but I have my doubts about their longevity and real efficiency, especially in hard water areas.


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## begreen (Aug 3, 2010)

Is solar a possibility for supplementing your setup?


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## btuser (Aug 3, 2010)

I'm going to try a drain water heat recovery first.  If that plus my constant bitching about the hot water can drop the overall usage to 100 gallons/day, I'll be in the market for a solar setup.  I'm already looking for the tank.  I I can score a large 80 gallon + dual coil indirect, or a 100 gallon single coil I'm going to take it and figure out what to do with it later.  I'd favor a single large tank with dual coils simply because I don't have the room, but its looking more and more I'm going to use a single coil tank connected to solar as a pre-heater to the main tank that will remain connected to the boiler.  The problem I see with this would be the necessity of the boiler still firing unless the solar tank was in the 140f and up range.  I'm thinking of digging a hole/box against my basement, placing the tank there and insulating with foam board to keep out moisture.  I really don't have any room where my boiler is now.   Right now hot water cost me about $2.50/day, so its a hard sell to the right side of my brain when the proper solar setup would run me $7,000.


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