indirect or not?

MrLeahy

Im trying to figure the numbers for the savings the indirect will add to an oil based system as our service man seems to think that it will.

Heated space is about 1700 sq ft- 2 zones with some baseboard and some cast iron radiators. We have a hot water system and oil fired cast iron boiler running at 1GPH 105MBH NET on .85 nozzle. According to recent inspection the boiler efficiency is ~86%. Manual states idle loss of 2.1. Hot water capacity for the boiler is 13.5 gallons.

The indirect Im considering is 41 gallons with idle loss of 1.4 (Mega-stor). The tech says that adding this indirect and cold-starting will save $ in the long run.

I dont quite see it that way. Here are my 3 primary concerns:

1. I was always under the impression that cold-start is really bad for cast iron oil based boilers - scale buildup and consequent efficiency loss.

2. Keeping 41 gallons hot at 1.4 idle loss seems awfully more wastefull than keeping 13.5 at 2.1 Or am I wrong?

3. We dont have any problems with hot water as there is only 2 of us. We have 1&1/2 bathrooms. Dishwasher once a month maybe, our washing machine is brand new efficient unit. No jacuzzi. Showers are short - mine 10min max, wife s 20 min max

If anyone can shed some light on this Id be most appreciative!

jp_2

maybe electric?

you could figure out yearly usage, if its pretty small and electric water heater might make more economical sense?

MrLeahy

.

jp, thats what I might do - I just have to run the numbers.

The thing I dont understand is why everybody advocating indirects esp in low water usage situation. The ratio btw keeping smaller amount at higher loss vs keeping large amount at smaller loss seem to favor the former. No? Is there a formula one might use to figure this out?

jp_2

average america use

most people use tons of hot water, big tubs, long showers, body wash sprays that require lots of GPM.   so then an indirect makes sense.  but if you really cut down on use, I think an electric would be reasonable, BUT do the number so you have a better idea.



I had planned to use the kohler laminar flow waterfall tub filler, then I saw the minimum flow was 7 GPM,  the mini smart hot water tank max out at 3.5 GPM.  so there is a good example.



I personally have not had a hot water heater for 7 yrs.  heat my water on the stove.



No wise cracks BRad white

Al Letellier_21

indirect or not

Here are some real world number to consider. I heated 1000 sq feet 35 years ago, just two of us. Started out with an Arco steamer with Timken burner and an oil fired water heater......450 gallons a year.

Installed a Thermodynamics boiler with coil in 1980 and added lower level heat going to 1500 square feet........800 gallons a year

In 2004 installed Weil WTGO-3 with coil.......750 gallons a year

In 2007 pulled coil, added indirect ( Plus 40 ) and TEKMAR outdoor reset and guess what...back to 450 gallons with 50% more load

Go figure.

CMadatMe

Blind

I'm not meaing nor intending to be rude but your concerned that an indirect may not be efficient yet you have a 100,00 btu boiler heating 1700 sqft. Your concern should be reducing that load because that boiler is WAY oversized. Do a heat loss and you will see that you only need half or less. That 86% is a not a true statement as to the "Heating Systems" efficiency. It only relates to the burner efficiency. So what that your making 100,000 btu's at 86% efficient. In reality the system is more like 50%. All that extra energy being made that doesn't need to be made is going up the chimmney...This is the main reason why a cold start boiler is more efficient. Reduce chimmney loss.

chapchap70

less loss through the flue pipe

An indirect would give you less idle loss because it does not have a flue pipe.  The boiler with tankless coil set at 160 or so has to come on to maintain temperature.  With an indirect, the boiler temperature could be lowered a bit while still giving you hot water and this would mean less standby losses up the chimney.  I don't know where you got the 2.1 standby/idle losses on the boiler but that seems very low.



If your house is occupied and the hot water is being used, the boiler should come on once a day or more so it would not truly be cold start since the temperature probably would not go much below 120.  This is not the same as leaving your boiler off for the summer. 



Since the boiler is maintaining temperature anyway and electric rates are higher than oil rates per BTU in many places, it probably doesn't pay to get an electric water heater.



If your coil is still working well, it all depends on payback time because it probably isn't cheap to buy the indirect and have it piped in.   My thinking is if you lower the aquastat settings so you have an idle loss of 6 degrees per hour instead of 11 or so, you would save 25 to 30 gallons per year with an indirect over a tankless coil.



One thing you might want to consider is the Beckett Heat Manager.  http://training.rwbeckett.com/modules/Heatmanager/Auto/Beckett-HeatManager-autoPace.html

icesailor

50% more load?

Where did the 50% more load come from?

If you have a WTGO-3 and you are running it as a clod start, and you don't ANNUALLY open the front after cleaning from the top, and clean the black kibbles and bits from the chamber, you are wasting energy. And that includes removing the rug and scraping all the cementious material UNDER the rug and scraping up the sides between the sections. WTOG's run no lower than 135 degrees operating and 170 high limit will have a fine brown ash after a couple of years. You don't need a soot saw to get it out. Just a small fluffy brush.

I think that someone has played fun with numbers in the past.

I have a WTGO-3. I sat in my living room one Sunday and my burner never once came on in 8 hours with the clock thermostats down 10 degrees and the temperature only dropped 7 degrees when it was 12 degrees out. Where's all this stack loss?

With just a tank less, and no storage tank, you are using 100,000 BTU's to heat whatever small or large amount you use on demand. With a storage tank, the circulator only uses the stored latent heat in the boiler water.

This cold firing is just a really bad idea. Now, the Mod/Con boiler manufacturers are recommending annual servicing (cleaning) of their appliances because of water/condensing problems. That cuts into the cost savings.

The complete exhaust system on my 2001 BMW 325 XI wagon has a complete stainless steel exhaust system It has 130,000 MI on it and it is still original. My 2000 Ford E150 with 100,000 Mi had the exhaust system replaced at 95,000. The after market system that the dealer installed will be toast by 120,000 MI.

chapchap70

stack loss

"I think that someone has played fun with numbers in the past.



I have a WTGO-3. I sat in my living room one Sunday and my burner never

once came on in 8 hours with the clock thermostats down 10 degrees and

the temperature only dropped 7 degrees when it was 12 degrees out.

Where's all this stack loss?"



I've seen 20 degree loss in an hour on a 2.95 gph Weil McLain when the temperature was 45.  It does have a 10" flue and the water content is around 42 gallons.  I'm going to try to attach a spreadsheet file again which shows where I got my thinking from.  The boiler is a Peerless WBV-03 which has a water content of between 11 and 12 gallons.



I think his 50% more load comes from the fact that he started with a 1000 square foot house and now has a 1500 square foot house.



I wish I could have attached the spreadsheet so you could see the formulas but this gives some idea for those interested.

Al Letellier_21

Who said anything about cold start

Don't run it as a cold start. Am very aware of the Weil characteristics and ops...I've only installed about 300 of them, and I didn't fudge the numbers, I just know how to run my system. True the boiler is too big for the load but it works great and hasn't taken anything but a nozzle and pump strainer in years, no soot, not crude under the blanket easy maintenance and great efficiency. 70 degrees in the house all heating season and never have run out of hot water....can't wait to see the number when I switch to natgas, install my Rinnai continuum and my new Ultra 80 gas boiler.....it just keeps getting better.

icesailor

Indirect or not?

Al,

If you don't run it as a cold start, you don't get the crud under the blanket. The crud from cold starts comes from the condensing water that runs down the sides between the sections and runs under the rug.

Good on you to have Nat. Gas you can use. It's in front of my house, 500' away. The cost of running it and repairing the landscaping plus a new boiler makes it so I wouldn't live long enough to see a pay back. I have LP for my dryer. Amerigas refuses to give me a jar of Vaseline and a pair of used jeans with a hole in the back with my gas bill. Well over $5.00 per gallon.