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EfficientCanuck 03-01-2009 12:11 PM

Fuel savings from burner/nozzle reduction
 
Does anyone here have any experience with reducing the burner and/or burner nozzle size in order to achieve fuel savings? I have been adding additional insulation to my home and know for a fact that my current furnace is substantially oversized for the amount of hourly heat loss that my house now experiences. During the absolutely coldest days the burner only runs for 9 minutes in every 32 minutes (about a 28% duty cycle for my oil-fired warm air furnace).

What I'm trying to determine is whether it is cost-effective to replace the burner with a smaller unit that will allow me to use a smaller burner nozzle (the current burner is a Riello 40-F5 that is only 11 years old). Supposedly there will be a fuel savings if I do this, but I have no idea if i could see something as impressive as a 10-20% fuel savings or something as insignificant as only a 1% fuel savings.

Kevin

yuri 03-01-2009 12:20 PM

The furnace is designed to have a certain temp rise thru it. Smaller burner=less heat=potential for condensation/sulphur buildup/corrosion in the heat exchanger. I would not do it. The furnace may be slightly more efficient when it runs longer but a BTU is a BTU and what leaks out of your house must be replaced by equal BTU's. The house does not care how long that takes. If you have gas in your area use it instead and buy a 2 stage furnace. Oil is stupidly expensive vs gas in Manitoba. Electric heat is reasonable too, about the same cost as an 80% efficient gas furnace here.

Good Day Eh

beenthere 03-01-2009 12:25 PM

A reduction in nozzle size can save fuel.
How much, can't be determined from this soide of the internet.

However, the Riello is not a forgiving burner.
You'll need combustion test equipment to set it up proper if its not at its min firing rate already.
If not set up properly. It will use more oil. :eek:

Getting a new smaller Riello won't be cost effective if your 40 can't be downfired.

EfficientCanuck 03-01-2009 01:59 PM

Thanks for the input BeenThere.

What I can tell you is that the information on the furnace information plate does clearly indicate that the current burner can be replaced with the smaller Riello 40-F3. When this smaller burner is combined with the nozzle 0.60-60W it will provide 84,500 BTU instead of the current 112,700 BTU/hr that the current configuration is capable of delivering.

Just to let everyone that reads this post know if I do replace the burner it will be with the assistance of a fully trained and equiped burner technician. I would not attempt a job like this on my own at this point.

The key detail I'm trying to determine is what I could realistically expect to see for fuel savings.

Oh yes, to answer an earlier question natural gas is not available here in Prince Edward Island.

Plumber101 03-01-2009 02:12 PM

Quote:

Originally Posted by EfficientCanuck (Post 238711)
Thanks for the input BeenThere.

What I can tell you is that the information on the furnace information plate does clearly indicate that the current burner can be replaced with the smaller Riello 40-F3. When this smaller burner is combined with the nozzle 0.60-60W it will provide 84,500 BTU instead of the current 112,700 BTU/hr that the current configuration is capable of delivering.

Just to let everyone that reads this post know if I do replace the burner it will be with the assistance of a fully trained and equiped burner technician. I would not attempt a job like this on my own at this point.

The key detail I'm trying to determine is what I could realistically expect to see for fuel savings.

Oh yes, to answer an earlier question natural gas is not available here in Prince Edward Island.



Realistically you could increase the fuel consumption. If the furnace was sized for your house as it is then by reducing BTU's you could make you furnace run longer to heat the same space..Under sizing the furnace to your house
There are a number of varibles to sizing a furnace to name a few

Sq ft of house
Ceiling height
Duct work
Number of windows
How well the house is insulated
Either a 80 or 90+ %

beenthere 03-01-2009 03:03 PM

Check your current temp rise. Temp of air entering furnace, and temp of air leaving furnace. And post what it is.

Thats a fairly good drop in nozzle size.

The combustion chamber may be too large for that firing rate. Or it may not be.

A good tech would measure it before just down firing.
Along with temp rise, and current CFM the furnace is moving.

EfficientCanuck 03-01-2009 04:05 PM

As I stated in the original posting the current system is substantially over-sized. The burner only runs about 9 minutes in every 32 during evenings when it is -25 deg Celcius (that's about -13 deg F). Going on the facts as I see them I have no concerns in "considering" a reduced BTU furnace configuration (a heat output reduction from the current 112,000 btu/hr to 84,000). The demonstrated heat input requirement for the house is 9min/32min = 28%, 28% of 112,000 = 31,500 btu/hr. If I actually do go ahead with a burner/nozzle reduction that delivers 84,000 BTU I will still be well above what the house actually needs.

Here is some additional background information.

Back a few decades ago when the first warm-air furnace was installed the house was newly constructed. It only had single glaze windows. It only had R12 insulation in the attic. The basement and the basement header was fully un-insulated. Back at that time the original furnace was most likely sized properly. However, there have been many improvements over the years that have greatly reduced heat loss.

I recorded the burner cycle time over the last few weeks (during the coldest evenings).

yuri 03-01-2009 04:22 PM

I have a high efficiency gas furnace, 66,000 BTU output in a VERY well insulated house. It runs for 10 mins ON with 20 mins or longer off cycles with a 1deg F differential. I do not consider that a problem and it gets to be -35 to -40 C in Winnipeg. I do this work professionally and am not going to replace the furnace with a smaller one as it is not a problem IMO. I doubt if the fuel savings if any from what you are doing are going to be that worthwhile. A smaller furnace may be a bit more comfortable. There is no way to guarantee the % savings unless you talk to a HVAC professional design engineer. For longer cycles they now have 2 and 3 stage gas furnaces.

EfficientCanuck 03-01-2009 04:40 PM

Quote:

Originally Posted by yuri (Post 238767)
I have a high efficiency gas furnace, 66,000 BTU output in a VERY well insulated house. It runs for 10 mins ON with 20 mins or longer off cycles with a 1deg F differential. I do not consider that a problem and it gets to be -35 to -40 C in Winnipeg. I do this work professionally and am not going to replace the furnace with a smaller one as it is not a problem IMO. I doubt if the fuel savings if any from what you are doing are going to be that worthwhile. A smaller furnace may be a bit more comfortable. There is no way to guarantee the % savings unless you talk to a HVAC professional design engineer. For longer cycles they now have 2 and 3 stage gas furnaces.

Thanks for your input, Yuri. I'm not planning or considering to replace the entire furnace. I agree with you on the item of comfort. I don't have a problem with the current comfort in my house either. Furthermore, my burner on/off cycles don't bother me. I'm just trying to see if downsizing the burner/nozzle combination could be a worthwhile fuel saver for my situation. If it's not then I'll stick with my current heating system for now. It's only 10 years old. Still lots of years left before necessity will be knocking at the door.

Just curious though, can you tell me more about multi-stage furnaces?

beenthere 03-01-2009 04:47 PM

Its not will it heat your house.
That we're concerned with. As much as, will it use more, because you have lowered its thermal efficiency too.

You may not have a hot enough flame for good combustion, and heat transfer, it you lower the nozzle too much.

Lowering the flame temp by 200F is one thing.
Lowering it by 600F is another.

If the burnt gas temp drops too low, you get sulfuric acid formations(good reason to buy a new furnace shorty after).
Along with chimney repairs.
You may not be able to slow your blower enough to maintain proper temp rise. Which will also cause condensation in the furnace, and damage it.
You may not be able to reduce firing rate as much as you think.

I have nothing against down firing.
But, it has to be done with the furnaces combustion design kept in mind. And, maintain proper flame temp, and flue temp.

yuri 03-01-2009 04:47 PM

Check Lennox.com and look at the G61 and G71. The G61 fires at 80% of its total capacity for the first 10 mins and then goes to high 100%. The G71 can be used at 45/75/100% or modulating. There are no 2 stage oil furnaces but with electric you can use a high/low switch in milder weather. I imagine electricity is expensive in PEI as it is coal/nuclear? We pay 8c/kwh here for hydro.

yuri 03-01-2009 04:49 PM

Beenthere is absolutely right. I have done lots of oil and what sounds simple can create all those problems. Not worth the risk.

EfficientCanuck 03-01-2009 08:08 PM

Quote:

Originally Posted by beenthere (Post 238776)
I have nothing against down firing.
But, it has to be done with the furnaces combustion design kept in mind. And, maintain proper flame temp, and flue temp.

I have no intention at all trying to lower BTU output beyond what the current furnace is designed for. I fully realize that there are many serious potential problems that can occur if your go beyond the design configurations that are listed on the nameplate of the furnace. The design configuration on the nameplate of my furnace that offers the lowest heat output will supply 84,000 BTU/hr.

As Yuri had suggested earlier, it's looking like I'll have to track down a design engineer in order to get an estimate on the potential fuel savings. From what I'm hearing so far there appears to be no simple answer to my question.

EfficientCanuck 03-01-2009 08:21 PM

Quote:

Originally Posted by yuri (Post 238777)
I imagine electricity is expensive in PEI as it is coal/nuclear? We pay 8c/kwh here for hydro.

We currently pay 16c/kWh. Heating with electricity here in PEI isn't a cheap option. About 80-90% of homes in PEI are oil heated. There was talk of bring natural gas to PEI a few years ago, but it appears that the infastructure costs compared to the small market size don't produce financial numbers that are attractive. Personally i have no problem with oil heating. I just like to ensure that things in my house are running as efficienctly as possible and I'm not wasting opportunities for energy savings.


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