Is an indirect water heater really the most economical way to go?

Musicman1978

I have a Phase III 45 gallon indirect hot water heater being fed by a Burnham boiler with a firing rate of 1.36 gph. The system is about 7 years old and the boiler was tested to be 81% efficient during last season's cleaning. I put a timer on the burner, and the system consistently runs for about 1 hour in a 24 hr period during the summer months, which means at the lowest oil price I can find right now on the CT shoreline of $2.45, it is costing me $3.33 per day or about $100 per month   to heat water in a house with just 2 people.



Everyone says that the indirect system is supposed to be the most efficient but this seems to be pretty expensive to me considering I know people with gas hot water heaters that are paying only about $30 - $40 per month and using  similiar amounts of hot water. I was considering replacing the system this fall with either the new  Rheem or GE Hybrid electric heat pump water heater. There is a tax credit going on until the end of the year that would offset some of the cost. Is this typical of what I should expect with an indirect system? Would it be reasonable to assume I would realize any savings with the new system?

D107

Depends

FWIW i'm a homeowner; indirect in family house on LI. From what I've learned here, I'd say it depends on:

1-boiler efficiency, burner combustion; ours is 86%. then there's system efficiency and level of insulation on the indirect.

2-our boiler was sized relatively close to heating load by a detailed heat loss calc, burns only .6gal/hr. don't know size of your house but our 2000+ sq ft house with the 50 gal indirect uses about 120 gal/yr for hot water (only one person in house); and in summer uses .38gal/day or about $30/mo.

3- based on what i've learned here, i prefer an indirect to the instant water heaters that heat only upon use because from what i understand those units require a greater fuel/firing capacity. I believe in the practice of using higher storage capacity to cover any extra heat load from the hot water demand. That way boiler can be sized to heat loss, not hot water load.



A top HVAC pro looking at your system might be able to save you some $$.

Steamhead

Also

is your boiler in proper tune? That makes a BIG difference!



Which Burnham is it?

TonyS

Indirects are not very efficient

even if you have a good one that actually loses 1 degree an hour. If its a 40 gallon, that is 340 btus an hour lost. Thats over 8000 btus a day. This is not taking into consideration the loss of the boiler, if you have a 400 lb boiler filled with 5 gallons of water and it gets hot and then sits there and cools, its ridiculous. Its not near as bad if you use a modcon as the heat source but still not a good idea. Now the mantra is keeping your water heater at 140 or more because of legionaires, this makes the heat loss even higher.

If you want to make all the hot water you need at exactly the temperature you want at 98% efficiency, use a Navien and if you have 6 baths and a whirlpool tub you will have no trouble affording 2 of them( they daisychain together) I lived with a indirect and for the last 2 years with a Navien. There is no comparison!

Mark_129

Don't go hybrid...

If you're looking to save money, going electric (even the so-called "hybrid" water heaters, which are heat pump water heaters) is the wrong answer. I haven't updated my spreadsheet for the costs you state, but I would estimate that even a hybrid water heater is going to be 2-3x as expensive per unit of heat output compared to oil because electricity is expensive. Convert kWh to BTU and you'll see.



I have a Burnham that I'm replacing (see other post) that also runs for about 1 hour a day. The main reason is because it maintains the boiler at 160-180F all year around. Does your boiler do the same? If so, that's the majority of your heat loss. Based on what I saw on the web, the Phase III indirects have 2" foam insulation, so I would guess that the heat loss is not from them - but from your Burnham. Depending on the clothes washer and dishwasher and the settings on them - these could also use alot of hot water.

D107

Flow rate

Tony do you know how many gpms with the usual temp rise the smallest Navien 98% (15Kbtu) can sustain? And can the venting be linked to a mod-con direct vent so as to have only one exhaust line as it exits the structure?



thanks.

TonyS

flow rate

David, the smallest Navien is the 180...thats 180000 in and the lowest it can fire is 15000. here is a link to all the specs

http://www.navienamerica.com/product/ts_heater_02.aspx?skin=ts_heater

Steve Rockwell_2

Cannot Agree With You

My experience has been great with an indirect.



WM Ultra (installed 2004) with WM 40 gal indirect. Summer gas bills are $20-30 over the past several years, that's for a family of four.



No doubt winter water heating costs would be higher, as 1) water has to heat up copper pipes while going upstairs, and 2) we tend to take hot showers rather than warm as in Summer.



We also turn down the temp on the indirect in Summer - it's in the "blue zone" on the control atop the indirect, but plenty hot for dishwashing, showers, etc.

Bob Bona_4

be sure

the boiler is set up for "cold" start.

Tell us what model the Honeywell grey box is on the boiler.

I lost track of the jobs I have been on where an indirect is there, and the boiler is still set up to maintain 160 or whatever. Sometimes it's because someone didn't know how to wire in the indirect pump relay to start the burner on call, sometimes it's a vain effort to compensate for undersized piping/pumps, sometimes it's b/c..ahem...the oil co wants it that way

Pics?

CMadatMe

MusicMan

That's an awful big boiler. Be curious as to the size of the home and whether it has average insulation and updated windows.



 Have you considered turning down the aquastat in the summer months on the boiler from 180 to 160? Could save roughly 7% right there. Also install a thermostic mixing on your domestic hot water supply and turn down the water temp for the summers months. We tend to take cooler showers in the summer than the winter.



You have two issues that are hurting you. Issue one, the boiler efficiency is killing you. Your sending 19 cents of every dollar into la la land. Issue two, boiler is most likely short cycling. Not alot of storage there for a boiler firing at the rate you stated. When you say 1 hour in 24 hours what intervals are we talking about. It's that six 10 minunte cycles, two 30 min cycles, 4 15 minute cycles? Is there a re-circ line on this system?

CMadatMe

GPM Calculation

David,



Calculation is gpm x temp rise x 500 = btu required. Just reverse the math.



180,000 divided by 500 divided by rise = gpm



For me would calculate out to 5.5gpm

TonyS

Steve, im not saying the indirect didnt do a good job

I'm just stating mathematical fact. 40 gallons of water=333 lbs...1 degree an hour=333BTUS an hour x24=7997 a day x 30=239904 a month x 12=2878848 divide that by 92000 btus in a gallon of propane and you used 30 gallons of propane for nothing. I can run A Navien for a 2 months on on 30 gallons. Remeber I just figured the heat loss in the indirect, the real figure including the boiler loss and the less than 100%efficiency on the propane, the real figure is more like 45 gallons a year. Multiply that by all the hot water storage tanks in this country alone and the number is staggering.

Musicman1978

Is an indirect water heater really the most economical way to go?

Musicman1978

Is an indirect water heater really the most economical way to go?

Thanks for the replies so far. To answer some questions, the boiler is a Burnham V8 Series model PV84WL-TBWF - It is a 159,000 BTU unit heating a 2500+ square foot home in a hydro air heating system. The aqua stat is a honeywell type L8125A,C. It is set at 160 degree upper limit, and there is no low level set point - If nothing calls for heat the boiler will go cold. The indirect water heater is a Triangle Tube Phase III model TR-45 with a 46 gallon capacity. I have the water temp turned down to about 115 degrees in the water heater. It does have a recirculating line, because the master bath is at the opposite end of the house. We are not using hot water for anything but showers and the dishwasher - The laundry is done in cold water most of the time.

Here's a couple of pictures

TonyS

your boiler weighs 640 pounds

so lets just figure when its filled with water minus burner and jacket we have 500 lbs that we are going to heat up to 160 degrees and lets say cast iron has the same specific gravity as water( it doesnt..its 7 times higher) and now , after the indirect is satisfied it is going to cool down to room temp..and it will do this rather quickly because you can be sure it loses more that 1 degree an hour...500lbs x 90 degree drop=45000 btu. Thats how much heat you lost after you shower in the morning and come home in the evening not including the water drop in the indirect. That is why when people talk about indirects, you will hear really vague terms like "really efficient" or"super low loss" these terms are used to replace simple math. Kinda like window salesmen. Even with controls that post purge the boiler, you can only post purge to the temp of the water in the indirect which is 140 or should be because of legionaries disease. Install a Navien and you will be very pleased.

CMadatMe

The Hydro Trap

Sixty btu's a sqft for heating is outrageous. Boiler was sized to the air handlers and not a heat loss. Your worried about $100 month for domestic. Should be worried about all the money you are wasting to heating. Are your heating cost acceptable because your neighbors spend the same? The indirect is not the problem, it's the 81% in-efficienct oversized boiler.

Bob Bona_4

the boiler

has a Honeywell R8124A aquastat with a low limit. Which means it is maintaining a minimum temp 24/7/365. There goes energy savings. You want a R8148, or the new electronic equivalent- high limit only control for true cold start.

I would be interested in knowing what size piping runs from the indirect to the boiler, and how the indirect controls the boiler.

I agree with the others that the boiler is likely a little oversized, but it is what it is, let's make sure we are getting the BTU's as efficiently as we can to the hot water tank at least.

Where's one of the air handlers? Attic? Thus the antifreeze I see oozing from the Hyvent. Might want to see about getting a freezestat up there instead, flushing the glycol out if you think you can do with out. The glycol is inhibiting heat transfer by about 20%. At the very least, have the Ph and concentration checked out. The glycol will eat the system alive if left alone.

And we are sure there is no thermal heat migration to the air handlers on off cycles? That can suck up some heat if a checkvalve is stuck. The hydro coil can get warm, but you'd not know it since the fan isn't running. And the A/C would be not performing as well as it should.  

Thanks for the pics.

TonyS

Bob

His picture shows a triple acting but it is very easy to eliminate the low limit and use it for cold start. But you are right, if the boiler is maintaining temp then the math becomes even worse.

NRT_Rob

I think you're right and wrong

I am not sure that 1 degree an hour is a good estimate for all tanks, first of all. So I think you're overstating there for a lot of tanks. but certainly insulation level on the tank matters.





I think one thing getting confused in this thread though is TYPE OF BOILER on the indirect.



high mass boilers waste a lot of heat per cycle when they are not using it to heat. low mass boilers don't. so high mass boilers are pretty inefficient on an indirect.. in the summer. low mass boilers are significantly better. Both are fine in the winter when you are not likely to let the boiler go cold in between demands, especially with post purge or reset controls.



Indirects still provide better quality hot water over a wider flow rate range than most on demands, but if efficiency is the issue, I would say simply: if it's cast iron, use a separate heater for domestic. If it's wall hung or low mass, use an indirect.



Brookhaven labs did a report on this.



http://www.nora-oilheat.org/site20/uploads/FullReportBrookhavenEfficiencyTest.pdf

The Steam Whisperer (Formerly Boilerpro)

I think you are using the wrong numbers.....

specific gravity compares the density of iron to water...iron is 7.8 times more dense than water.    However, the specific heat, which compares the heat holding capacity of iron to water, iron is 1/9 that of water.  In other words water holds nine times more heat than iron per pound.  500 lbs of iron cooling 90F would ony be 5000 btu, not 45,000 btu.



Other issues with  instantaneous water heaters include typically shorter lives,the need to upgrade the size of gas lines in homes, and the fact they are gradually being "oulawed" in many areas because the gas grid cannot handle the massive instantaneous load they can cause first thing in the morning. The gas grids of most major cities are low pressure and already overtaxed by large loads midwinter.

I also have a 40 gal  indirect and fuel usage is about 1/2 a conventional 40 gal chimney vent model when tied to a higher mass condensing boiler.   We use a total of about 17 Therms per month in gas, including cooking, dryer, and indirect water heatinfor two people, one which takes long hot showers daily.  This is about 56,000 btu/day or about 1/2 gal of oil a day.

Part of your high gas usage is probably the recirc line....they through off alot of heat.

Robert_25

Recirc. system eating btus?

I agree that your fuel consumption seems very high for only two people using hot water, especially if your laundry is washed with cold water.  I am wondering how many btu's are being lost through that recirc. system.



If you would like some data for comparison, here is my story:  My home has a 6-section cast iron Weil McLain oil-fired boiler that is fired at 1.8 GPH, and a 30 gallon. Weil McLain Indirect.  The boiler is kept at a minimum temp. of 140 degrees, there is a Beckett Heat manager installed, and the indirect is set at 140 degrees.  My wife and I each shower every morning, and we run the dishwasher roughly every two days.  We have a front loading washer and do a load of laundry on "warm" about every two days.  I have an hour meter on the oil burner, and we average about 1.1 gallons of fuel per day.



-Rob

Bob Bona_4

I'm aware

of that, Tony and it did cross my mind. But, seeing how the boiler was piped, I had major doubts someone would attempt to modify the aquastat.

Plus, not sure if that would be very litigous free;)

Bob Bona_4

I'm with you

Is the recirc line at least on a timer? 

TonyS

Boilerpro

you are right, specific heat of iron is .12. I thought that number looked a little high .

As far as shorter lives that remains to be seen, Navien provides a 15 year warranty on the exchanger and 5 years on parts, better than most modcons used to fire these indirects. As far as gas lines go we have no problems in our city as all low pressure mains have been replaced with medium pressure years ago. Most Naviens I sell are LP as that is where the payback really shines.

Even with the cast iron losing 5000 and the 5 gallons of water losing another 4000 that is still almost 9000 btus lost. thats enough for me to take a shower at 2.2 gallons per minute for 7 minutes just in the boiler.  I understand a half a gallon is relatively low but wouldn't a quarter gallon be better?

Musicman1978

Is an indirect water heater really the most economical way to go?

Thanks for all the replies, I am getting some good ideas here. Here's some answers to some questions, and a little more info -

The on demand sounds like a good idea, I have heard both good and bad about them, but it is not an option because natural gas is not available in my area, and I'm not interested in going with propane - it's just not worth it to me. I don't think the electric on demand would be good for my application.

As I said before, the aquastat is set up with no lower limit - the boiler can go dead cold if nothing calls for heat, so there is no losses from maintaining boiler temp.  The indirect doesn't call sometimes for hours, so the boiler starts from cold almost every time ( this does seem like a place where a bit of waste is going on ). The piping to and from the boiler is 1.5", and the indirect controls it's own circulator. If when the circulator is activated, the boiler temp is above the upper limit cut off, the burner does not fire until the temp drops below about 150 - 160 degrees. When the thermostat in the water heater is satisfied, the circulator shuts off and so does the burner regardless of whether it reached the upper cut off.

The system has 2 air handlers, both are in the basement, the house is a single floor layout except for the room over the garage.

There is no glycol used in the system, it is just water.

There is no significant thermal siphoning coming out of the boiler, but maybe a bit from the water heater - I am going to look into that and maybe do a thermal loop to break it.

The recirculating line is on a timer, it runs for 10 minutes each morning before my shower, then shuts off for the rest of the day.



Now more questions for you guys:



The boiler was available with 2 nozzle sizes, the 1.36 gph which is what I have, or a 1.05 gph that will bring the output down to about 125,000 BTU and raises the advertised efficiency up a percentage point or two. Is this worth doing?

The talk about the energy wasted bring the boiler back up from cold to maintain the water heater several times a day got me thinking - maybe I should try shutting the boiler off after the showers in the morning and turn it back on about 1/2 hr before showers the next day to see if it burns less??

The heater is well insulated and would keep the water reasonably warm for the rest of the day, and it does recover very quickly. Plus I am pretty sure it would not burn for the full hour it runs now each day just to bring the water heater back up to temp one time.

What do you think?