View Full Version : retrofit oil boiler with gas power burner?
this is my first post to this forum.
i live in the philly area. i have a 1994 peerless WB-04 oil boiler with a becket burner and cast iron radiators (water). (peerless informed me that the WB is the same as the WBV). the domestic water is from a summer/winter hookup.
my oil tank is on the way out, and rather than replace it, since the cost of oil is so high, i am planning on using that money instead to convert to natural gas.
i am getting conflicting opinions from different contractors. here is a summary of the two competing approaches:
* new gas boiler (crown natural draft)
* indirect water tank.
* keep the WB-04 boiler
* replace the burner with a gas power burner (midco EC200)
* indirect water tank
* outdoor reset temperature compensator
* about $3000 dollars cheaper
on the face of it, approach (2) seems better for these reasons:
* a lot cheaper
* possibly a little more efficient
* doesn't junk a perfectly good boiler
* leaves open the option to go back to oil if that looks better in a bunch of years
I have a lot of questions.
(a) the gas boiler guys claim that the retrofit won't be efficient while the power burner guys say it will be just about 1% worse than the oil burner (which is 85% AFUE). if this is true it would still be more efficient than the gas boiler (82% AFUE). (plus the temp. compensator should improve things even more). anybody have insights on the efficiency of a gas power burner in a WB-04?
(b) the power burner guys say i will need a "barometric vent damper." I already have an "atmospheric damper" in a T in the vent that swings in on a strong draft. apparently a barometric damper swings both in and out. Why do i need it to swing out?? isn't that going to put exhaust in my house?
(c) i understand that the temperature compensator regulates the system's water temperature based on outdoor conditions. but, to me, this will only smooth out the system not actually save BTUs. The only way i can see it saving BTUs is by not losing as much heat out the vent (loss radiated from the boiler is not loss as the basement is a living space). are temperature compensators intended to save energy by reducing vent loss?
(d) if a temperature compensator works, why doesn't everybody have one?
(e) the gas boiler will have a mechanical vent damper to close the flue when not burning. that seems like a much better way to save energy from escaping out the vent. can i use a mechanical vent damper instead of the temperature compensator on my WB-04?
(f) the oil burner is loud. will the gas power burner be quiter?
thanks so much,
12-23-2007, 06:28 PM
The gas power burner will be closer to 78% then 84%. Due to the lower flame temp, heat transfer is not nearly as good as with oil.
The gas power burner is a little quieter.
You don't need the OD reset, but it saves fuel, more then the vent damper will.
If you realy want to save money, and switch to gas, step up to the plate, and get a modulating condensing boiler. It will add some money to your approach 1 price, but save you even more money. Especially when gas goes up again.
PS: No prices allowed.
Please edit them out, or a mod will.
12-23-2007, 07:54 PM
I agree with beenthere. We work on both oil and gas, install and service both. I'd never recommend a power burner for a residential oil boiler conversion. Too much cast iron in the oil unit and substituting gas will end up costing you more to heat. It was designed for oil, not gas. Get a modulating, condensing (Modcon) gas boiler from a company that both installs and services them. Be carful about getting a lower price from someone who claims to service them. Carefully question them about their 24/7 service coverage and then test it before you sign. Call on a Sunday night at 9pm and see what you get. When they get on the phone, tell them what you've got (using the new boiler) and see what their response is. You can always cancel the call and hang up and that's a whole lot better than having it installed by a company that really doesn't know diddly about repairs to the new boilers. There's a million people out there who will install it but they're scarce as hen's teeth when you need service. Just a word to the wise. ;)
oops, decided to put my reply into a thread w/ a better name... see "comparing gas boiler types"
here is my follow up question about the retrofit.
the retrofit guys say that with this type of boiler they can measure the vent gases. they suggested that this would demonstrate the comparable efficiency of the oil burner and the gas power burner.
the gas boiler guy says "that is only combustion efficiency, not heat exchanger efficiency"
the burner manufacturer tech support said "100% of the gas will be burned." if this is true then there is no combustion efficiency issue.
can the vent gases be used to demonstrate the total efficiency of the oil and gas power, including combustion and heat exchange?
12-24-2007, 02:59 AM
No, its a combustion efficiency test. It doesn't give a true heat transfer efficiency picture.
You go cheap and have the power burner installed. Then you'll be sitting in your easy chair with buyers remorse for the rest of your life.
We have no vested interest in what you have installed, the guys trying to sell you the conversion do.
Compare your oil price to your gas rate. It takes 1.4 therms(CCF) of gas to equal the 140,000 btu's input of a gal of oil.
At 84% eff for your oil burner compared to 78% for the power burner, it will take 1.512 therms of gas, to get the same amount of heat output your getting from a gal of oil.
thanks for explaining that the vent measurements are combustion only.
i was hoping to use them to verify the total efficiency. the problem is that different people are giving me different efficiency numbers and i was hoping to have an independent way to make sense of it all.
when you say 78%, where did that number come from?
12-24-2007, 02:46 PM
From the efficiency test of power burners that I have worked on.
Few get 80%.
cool. how do you test them?
(is there a thread somewhere which describes the testing?)
again, thanks much,
12-24-2007, 03:06 PM
I use a Bacharach Tech 60 combustion analyzer. Works on NG,LP,#2 fuel oil, and #1 kerosene.
You won't like the price of the 60, let alone any of the higher end ones.
ok, i have a bunch of questions...
(1) on the combustion test what would you expect to get for:
- conventional wet oil boiler like the WBV-04
- conventional natural draft gas boiler like the Crown Aruba
(2) i was thinking that there were two factors, combustion efficiency and heat xfer efficiency. since the the midco tech support guy said "the power burner will burn 100% of the gas" and because below you explained that the cooler temp of NG combustion would mean less efficient heat xfer, i had assumed that the problem was in heat xfer, not combustion. what percent of the inefficiency in these boilers is combustion inefficiency and what percent is heat xfer inefficiency?
(3) the reason i had asked about verifying efficiency with combustion testing is that i might strike a bargain with the guy who wants to install the gas power burner. we would measure combustion with oil and then with gas. if the gas wasn't approximately the same as the oil, then he would take the unit back. would comparative combustion testing on my boiler w/ oil and than w/ gas be an effective way for me to see if i am getting the 84% efficiency he says i will get?
12-24-2007, 08:02 PM
The 04 with oil, anywhere from 82 to 84% combustion depending on nozzle size.
A ND NG boiler, average 78 to 82% combustion, varies with gas BTU content.
I'm sure the power burner will burn all the gas, but not get all the BTU's out of it.
The same you don't get all the BTU's out of oil.
He's doing a play on words.
To strike such a deal, you better have every T crossed, and every I dotted, and then have it notorized.
Even with the same combustion efficiency, the oil flame is hotter, and will have a better heat transfer rate.
Do you know what your gas rate is per therm?
If so, what is it.
What was your last per gal oil delivery price.
I don't sell oil or gas. So I have no vested interest in which fuel you choose.
I just don't want to see you post later that you have a higher heating bill with gas then you did with oil.
A ND NG boiler will have a better heat transfer rate, then converting your 04 boiler to gas.
Simply because it was designed for gas.
thanks again for responding.
ok, so it seems you can use your combustion testing as a pretty accurate means to compare boilers. very interesting! almost like an EZ way to approximate AFUE, as your numbers reflect that pretty closely!
(those oil boilers are pretty good, huh)
my gas therms are $1.29
my oil is $3.30
last few years i have averaged 900 gallons of oil
i have used this calculator to estimate the price i would pay for gas heat at various efficiencies:
12-24-2007, 10:26 PM
Look into the Crown Cabo II or Bimini. They are more efficient than the Aruba and designed to burn NG. As Beenthere has already stated your current boiler is designed for oil. You will suffer overall system efficiency losses that are not easily measured with the gas power burner.
Also getting the new boiler is a good time to have heat loss calcs performed to be certain it is sized correctly.
12-24-2007, 11:13 PM
I'd add about 15% to what it says gas will cost you.
I ran one on one of my spread sheets.
And a ND NG boiler should cut about 900+ bucks off your heating bill compared to your current oil boiler under the same heating loads, at you current oil and gas rates.
i figured that i would save 45%, about $1400.
i got that same result from excel sheets found at two different sites.
here is the link for one of them: http://www.eia.doe.gov/neic/experts/heatcalc.xls
the numbers i plugged in are:
oil 3.30 / gal
ng 1.24 / therm
oil boiler: 85%
gas boiler: 83%
it was based on this that i decided to convert to gas from oil.
is there something i am missing?
12-25-2007, 11:19 AM
I used 1.29 for your gas, and 3.30 for oil.
80% for the gas boiler, and 84% for the oil boiler.
And based it on the 900 gals of oil you posted.
Which is about $1200.
I said 900 bucks + to be a little conservative, since many times what is figured on paper, and what it actually comes out to, is off by as much as 10 to 15%.
might the error also go in the other direction, eg, if the oil boiler isn't really up to 84%?
12-25-2007, 03:44 PM
Seldom. If ever.
I wouldn't ever tell a customer to expect as much as those on line calcs say.
well, this is a setback.
it makes converting to gas seem less attractive, relative to just staying with oil and upgrading my oil tank.
what do you suppose is the source of error in the spreadsheet calculations? it seems it would have to be that they are over-estimating the efficiency of the gas boilers.
12-26-2007, 04:24 AM
Heat transfer efficiency of the boiler. They can only make the cast iron so thin.
Oil with the hotter flame has an advantage.
Those calcs presume all things to be equal. And base their iutput on fuel BTU content, and cost alone.
With your rates, a new ND gas boiler will save $9,000.00 plus over the next ten years if the fuel rates don't change. Even more if oil goes up at a higher pace then gas.
not following you here. did you have a look at the spreedsheet i pointed you to?
the numbers you plug in are:
(1) efficiency of gas boiler (i put in %82 for ND, based on the AFUE)
(2) efficiency of oil boiler (i put in 85% for my peerless, based on the AFUE)
(3) cost of gas therm ($1.24)
(4) cost of oil gallon ($3.30)
the calculator provides:
(5) BTU content of oil
(6) BTU content of gas.
those 6 numbers are all it uses in the calculation.
using the numbers above, and my average of 900 gallons per year, i get that oil will cost $2970 and gas will cost $1703 for a savings of $1267 per year.
what are you doing differently in your calculation?
(according to this calculator, for a savings of $900, the gas boiler would need to be 64% efficient)
12-26-2007, 05:41 PM
I used 1.29 (You posted that rate earlier) for the gas. My $900+ figure is conservative.
I used that online calc. You could get what it says, But I doubt it. Gas BTU content can vary by the hour. That calc figures the same BTU content for the entire year (1000 BTU's per CF gas ). You could be paying for 900 or 950 BTU's per CF of gas. As it gets colder, gas companies often times add different gases to keep the pressure up.
So those online calcs can show you a lot higher savings then what you will actually get.
Go back to that online calc, and change the BTU content to 900, and see what it says.
(yeah, sorry about the 1.29. i misremembered).
anyway, diluting the gas! do they charge the same amount????
12-27-2007, 05:10 AM
And maybe the standard content for your area is 900.
You can always call the gas company and ask. Will they tell you the truth. I don't know.
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