Outdoor Reset - Need Calming Vibes

Boilertrouble · February 5

Recently installed a new Burnham MPO-IQ Boiler with an outdoor reset that supports a forced air hydronic heating system and indirect hot water heater. Have been reading all the posts on this forum (thanks for amazing content!) and still have some questions.

The boiler is currently running for only about 5 minutes at a time by turning on at 120 degrees and turning off at 140 degrees with an outdoor temperature currently in the mid-40s in southern NY. I have a few concerns:
- Does only running for 5 minutes at a time and only reaching 140 degrees put me at any risk long-term with condensation issues in the flue, boiler, etc.? Is that technically "short-cycling"?
- I noticed my electric bill increased this winter. Is that due to the blowers running more often based on the lower boiler temps? On a positive note, I noticed less oil consumption of course.
- Last question, are there any posts out there already on how to "fully optimize" the outdoor reset. It looks like it can be configured in a multitude of ways, but I have zero experience on this one.

Thanks in advance for all your insights!!

hot_rod · February 5

The boiler only feeds the air handler?
Or how close is the boiler sized to the total load of the home.
The boiler should rise above the dew point of the fuel on every cycle. 10 minutes or more is considered an adequate boiler run time.

So too cold of operating condition, and too small of a load on the boiler it sounds like?

Boilertrouble · February 5

The boiler feeds three air handlers and an indirect hot water heater. It is 189K BTUs, which is the same size as what was replaced (a Weill boiler that was 27 years young). This is my first outdoor reset though.

KC_Jones · February 5

Boilertrouble said:
The boiler feeds three air handlers and an indirect hot water heater. It is 189K BTUs, which is the same size as what was replaced (a Weill boiler that was 27 years young). This is my first outdoor reset though.

If I was betting I'd say the boiler is oversized and that will cause it to only run for a few minutes at a time. How oversized can only be accurately determined with a heat loss of the house, which should have been done by the contractor that replaced it. Obviously based on your comment about what it replaced, that wasn't done.

So, just as a shoot from the hip standpoint, how many square feet is the house that boiler is installed in?

Boilertrouble · February 5

About 4,200 square feet; some at different levels of overall heating from a thermostat perspective (i.e., a bonus room is set at 60 degrees for most of the winter and a finished basement that naturally stays around 60 degrees).

Hot_water_fan · February 5

How much oil do you use on an annual basis? That'll show us how well, or not, you're sized.

Boilertrouble · February 5

Last year was 1,000 gallons. This year, if I was a betting man; I would estimate 850 (through either a milder winter or the outdoor reset).

Boilertrouble · February 5

Sorry. Just realized my model is MPO-IQ189B, which I guess is equivalent to 145K BTUs.

pecmsg · February 5

Boilertrouble said:
Recently installed a new Burnham MPO-IQ Boiler with an outdoor reset that supports a forced air hydronic heating system and indirect hot water heater. Have been reading all the posts on this forum (thanks for amazing content!) and still have some questions.

The boiler is currently running for only about 5 minutes at a time by turning on at 120 degrees and turning off at 140 degrees with an outdoor temperature currently in the mid-40s in southern NY. I have a few concerns:
- Does only running for 5 minutes at a time and only reaching 140 degrees put me at any risk long-term with condensation issues in the flue, boiler, etc.? Is that technically "short-cycling"?
- I noticed my electric bill increased this winter. Is that due to the blowers running more often based on the lower boiler temps? On a positive note, I noticed less oil consumption of course.
- Last question, are there any posts out there already on how to "fully optimize" the outdoor reset. It looks like it can be configured in a multitude of ways, but I have zero experience on this one.

Thanks in advance for all your insights!!

Sounds like something is not set up right.

140°f Return water is minimum so you need at least 160°f Supply.

Call the contractor back.

Yes 5 minuets is too short to stabilize the burn.

Boilertrouble · February 5

Actually, not sure if those BTUs are 100% accurate either; but am fully confident that the boiler is a Burnham MPO-IQ189B. It looks like it has three output measures - Burner Capacity = 182 MBH, DOE Heating Capacity = 160 MBH and NET AHRI Rating Water = 139 MBH. It has a burner capacity of 1.30 GPH.

Hot_water_fan · February 5

Last year was 1,000 gallons. This year, if I was a betting man; I would estimate 850 (through either a milder winter or the outdoor reset).

You're majorly oversized. About 2x what you need. It's got some mass (15G of water + a good bit of Cast iron) but still huge for the application. Air handlers have low water content, so you have a very responsive system (good) but prone to short cycling (bad).

Robert O'Brien · February 5

Boilertrouble said:
Sorry. Just realized my model is MPO-IQ189B, which I guess is equivalent to 145K BTUs.

It's about 3X oversized

Boilertrouble · February 5

I didn't do this before having the contractor select & install, but looking at the online calculators for BTU based on climate, square footage and size of the home; they are showing between 162 - 175 BTUs. How does the oil consumption component factor into determining the system is oversized?

Hot_water_fan · February 5

I didn't do this before having the contractor select & install, but looking at the online calculators for BTU based on climate, square footage and size of the home; they are showing between 162 - 175 BTUs. How does the oil consumption component factor into determining the system is oversized?

The online calcs are junk, simply. Every house is different and houses that are the same size in the same climate can have wildly differing heat losses. The boiler you already have is smaller than those calculators say and you're short cycling. They're worthless.

The fuel usage is reality based- it's what happened. From there, you back into the right size. Another way would be a manual J calculation.

Boilertrouble · February 5

So besides for buying a new boiler, is there something to do in the interim? Should I shut off the outdoor reset? It is keeping the required temp tolerances in very close range currently. Today it is using a low of 120 degrees and a high temp of 135-140 degrees.

Hot_water_fan · February 5

You can use a higher differential (30 vs 20 degrees), install a sizable buffer tank, or live with it. I’m sorry the contractor didn’t bother to properly size it.

STEVEusaPA · February 5

Not only is it oversized, but the outdoor reset is making it worse. Usually hydronic coils need hotter water, in general.
Outdoor reset is not good with oil in general, especially if multi zoned, and absolutely not if oversized unless you have a buffer tank.

pecmsg · February 5

Boilertrouble said:

So besides for buying a new boiler, is there something to do in the interim? Should I shut off the outdoor reset? It is keeping the required temp tolerances in very close range currently. Today it is using a low of 120 degrees and a high temp of 135-140 degrees.

Install a buffer tank

Boilertrouble · February 6

Or I could let my wife & kids blast the thermostat. I feel like that would be against everything I was taught by my father as a child though.

Hot_water_fan · February 6

Or I could let my wife & kids blast the thermostat. I feel like that would be against everything I was taught by my father as a child though.

Ha of all the ways your kids will spend your money, this one is minor.

Boilertrouble · February 6

Anyone have any thoughts on the cost for a buffer tank and how to ensure one is appropriately sized? I obviously didn't do the appropriate homework on the install of the new boiler (lesson learned).

EdTheHeaterMan · February 6

Increasing the differential on the operating control is the first step. That is a DIY that will cost you nothing.

Some may disagree, mostly because this boiler is already super efficient and is operating with a low exhaust temperature (Stack Temp.) but you may reduce the short cycles a little by changing the firing rate from 1.30 GPH to 1.00 GPH by using the burner settings for the next smaller boiler size, the MPO IQ 147B. The burner you have is able to be set for that size boiler. You will need a professional to make that adjustment because you need to have a combustion test completed for the new firing rate. That will get your boiler to act like a 30% smaller boiler. In the scheme of things this adjustment is the least costly. If you can get good combustion numbers, this is the way you will operate it for the remainder of its life.

Adding a buffer tank is the next step. a little more cost involved but when you heat up more water, it takes longer. Also, that water will take longer to cool down, so you will get longer burner on times. With those three corrections, you may get 20 years or so, of efficient use from that boiler.

Boilertrouble · February 6

Ed - thanks for the alternate solution! Would that both stop the short cycle and use less oil?

Also, would the owners manual outline how to increase the differential and is there any setting you would recommend?

STEVEusaPA · February 6

You size a buffer based on the btu output of your boiler, the btu requirement of your smallest zone, desired runtime, and desired delta T
As an example…

Outdoor Reset - Need Calming Vibes

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