Oil Hot Water Boiler Cycling

Burntoacrisp

1st post! Hello to all. I have a low volume oil hot water boiler, Dunkirk DPFO 3 section.

My question is currently, when there is a call for heat it will run for approximately 5-6 minutes before it hits the high and turn off. It will then fire again after water temp drops to set point for approximately 5 mins again to hit high. Is this acceptable? Should I drop a nozzle size to enable longer runs for more efficiency. It is my understanding that long continuous runs are more efficient. This is a newer well insulated home, outside temps 10-15 degrees during the cycles described above. Finned baseboard.

Thanks in advance to all who post!





Double post! Sorry!

Robert O'Brien

Oversized

It's oversized. A reset control will help with the cycling,I'd go with a Beckett AquaSmart,it's a direct replacement for the existing Honeywell control and can use a wireless outdoor sensor,the high limit diff is fully adjustable and that will help tremendously with the cycling.The firing rate can be dropped by someone who knows what they are doing and has a combustion analyzer. If it has a tankless coil,dropping the firing rate may adversely affect the DHW.

Steamhead

Are you sure

the circulator is working properly?

Burntoacrisp

Short Cycle

It was installed with a indirect. It is currently not being used at all. So lowering the firing rate won't affect that. I have combustion analyzer to check the unit. The AFG will require a low fire baffle and new static plate. As for it being oversize the design temp is -30. And the indirect I'm sure was taken into account.  2000sf I'm getting pretty good efficiency, I would just like to wring out a little more!



What is considered a "long run" vs a "short run"?

Burntoacrisp

Circulator

 Yes, circulator cycles on/off  when it should.

Paul48

Micro-zones

Is there multiple zones, and are they very small?

icesailor

Cycling:

I think that you might be stepping over a $10.00 bill to try to pick up a dime.

There are a lot of oil burner technicians that claim that they can radically down-fire that unit and have it work fine. I've never been able to do that and I'm not one of them. Especially with an AFG. There's a limit to how low you can fire an oil burner and still have efficiency. At least that's my experience.

Maybe with a Riello,,

A little pet dander on the fan and it all goes out with the trash.

IMO.

Wayne M. Lawrence

stack temp?

Hi, I'm not familiar with this boiler, but curious. Is this a direct vent, or is a chimney used? If vented with a chimney, what is the stack temp? Is it an exterior chimney, is it lined? The stack temp in my opinion will determine what route you will have to take. Both short cycling, and extending the run cycle when downfiring will have adverse effects due to chimney condensation problems if the flue gas temp drops below dewpoint.

Burntoacrisp

$10 for a dime

I am leaning toward your opinion. I not so sure I want to go much lower. I am currently running a .65 @ 140psi giving me approx. .749 firing rate. If I drop lower I will have to move to FO head. So what does this mean? Maybe .50 to .75 increase in efficiency if I am lucky. Maybe a increase in condensation too. It is a direct vent with a short stack run. All this for an increase of maybe another minute of on time.

Burntoacrisp

Zones

No. All good size zones.

icesailor

Short Cycling:

I'd be more concerned with soot making up. Unless you have filtered the fuel to the max, and that includes two Garber Spin-On types and NOT, any canister types, those small nozzles under .75 GPH have a real propensity to clog up. Your 140# at the nozzle entrance will become .25 GPH at the outlet because of restriction through the strainer. Causing the temperature of the flame to drop, soot formation and high CO. And that $1,000+ digital combustion analyzer won't fix it. That's why you need one with a printer so that when you are done, you have an accurate record of what it was doing at the time you set it up. And when it goes down the toilet, and creates a huge problem, you can show that when it was set up, it was fine for your insurance company. Otherwise, it is like unprotected sex. You never know what you might get.

In my experience.

Burntoacrisp

icesailor

Haha! I definitely would not want my boiler to get herpes! I have a wool felt filter at the tank and a Garber (10 micron) at the burner. So far so good with existing setup for past 10 years. I think I am going to stay with the existing setup. It works, so why mess with it for a dime? Thanks for your input and everybody else too!

Zman

6 per hour

The number that is thrown around for short cycling is more than 6  per hour. You seem to be right about there. What is the differential between the boiler on vs boiler off? Stretching this number may be the easiest way to optimize you cycles. You want to be sure not to go so low that you impact performance or cause boiler condensing.It may be possible to combine this with Robert's suggestion of ODR.

On a warm day you could run 150-170 and on cold day 170-190.

Doubling your on off delta t will double your run time (almost).

Carl