New Gas Boiler "short cycling"

Meet with the installer with your list of questions.

A fast purge would be a good idea to eliminate questionable flow.

This fill valve has a lever on top to enable fast fill/purge function.

Watch him purge the system, the lever on this valve pointed up. This confirms the system is mostly air free and should circulate 5, 6 gpm or more depending on the pump model.

Show him your measurement of the entire fin tubed sections and this generic output chart.

If you know the fin tube brand you can zero in on an exact number. Most brands of 2-1/4" fin tube are similar output.

Get the boiler up to 180, start the pump, observe the supply and return.

If it leaves the boiler at 180, returns at 160 the average temperature in the fin is 170. Give it some time to reach equalibtrium. This condition is when neither the supply or return temperature is moving up or down.

On this chart, blue lines, with AWT of 170 a typical fin tube puts about 425 btu/ foot X 77= 32,725 btu. That is all that can realistically be pushed through the fin tube regardless if you have a million btu/hr boiler.

At 6 gpm through 3/4 copper you are right at 4 feet per second flow velocity. Beyond that flow velocity (speed) the system will become noisy from excessive flow, a hissing sound. No need to go there.

Adjust these numbers to the operating condition you can obtain at the time of the visit. The room temperature at time of testing for example. The chart a few posts up allows for the ambient air temperature correction.

With both of you there witnessing the actual operating conditions, temperatures mainly, the facts should be clear.

If you report back with some actual data I can plug it into the software and get more accurate. Pump model, temperature leaving and returning at the boiler. Confirm the fin tube lengths, a pic of the fin tube element with a tape measure on it.

Should be a fixable problem regarding a lack of flow problem. The purge hose will give you a good idea if there is a major blockage. It should fill a 5 gallon bucket in a minute or less if 5 gpm is flowing.

The oversizing is a bigger challenge.

Any pics of the before boiler and it's piping to see what may have changed?

I prefer the pump on the supply side of the boiler after the expansion tank, but not a dealbreaker, this system should work as shown.

Don't get too hung up on the systems ∆T. It should and will change as the load on the home changes. It changes as the boiler temperature is changing. It is merely an indication at any point in time of how much heat is being transferfed into the space.

This is a good motto for hydronician to live by

Now in your case you have a fixed speed circulator so flow rate is pretty stable. Use the hydronic formula to determine how much heat is being moved, with accurate supply and return temperature known. I'm thinking that 007E is moving 5-6 gpm based on the info you provides with fin tube lengths and assumed piping and fittings.

500 X flow X (∆T)

When the home is cold you see a wide ∆, indicating the system is transferring a lot of heat. As the space warms the ∆ will close, less heat is being transfered.

Thermal Equalibrium is a point when supply and retrurn temperatures stablize, not going up or down. Defined like this:

This graph is probably close to your system.

A 50,000 btu system with a 70°space temperature and the boiler operating at 180 SWT, another look at how the ∆ (bottom axis) the ∆ between air temperature and boiler supply, changes the amount of heat transferred

Could be there is nothing wrong other than the boiler not matched to the amount of distribiution?

Your comment about an even larger boiler connected to the amount of fin tube you have did not short cycle ever, just doesn't pencil out baed on the Laws of Thermodynamics, and all the formulas, graphs and math I presented?

Maybe something like this happened (one possible scenario):

The original (old) boiler was oversized for the house's heat loss and the radiation.

New boiler is a better fit for the house's heat loss but still a bit oversized and oversized for the for the attached radiation.

Assuming for a moment nothing has changed with the radiation (the flow is good) and the new boiler is a bit smaller. So why is it doing what it is doing, the short cycling ?

Maybe just maybe, the original boiler DID short cycle (when new). As a Band-Aid type fix to not replace the (then new) boiler they simply installed a delay timer in the burner circuit to eliminate the short cycling. Unknown to everyone involved with your old boiler's replacement the delay timer went away with the old boiler.

If this is a seasonal home maybe the radiation was never sized correctly for actual design day temperatures.

Was there any freezing damage from water not properly removed in the Winterizing process that caused some of the issues you mentioned in the last post ?

I think it's time to go back to square one here.

What is the heat loss of the building under design weather conditions? Manual J.

What is the actual capacity of the installed radiation? (feet of fin tube, type of fin tube, any enclosures on the fin tube.

Make and model of boiler

What is the net BTUh output capability of the boiler as installed?

What controls the system? (thermostat, type; aquastat, settings)

What is control logic? (thermostat controls pump? thermostat controls boiler? thermostat controls boiler? Aquastat controls boiler? both? Lots of options there)

All short answers… but without them we're all really just guessing.

With only 57' of fin tube almost any boiler that is not a condensing boiler is going to short cycle. Your baseboard is only good for 31,350 btu/hour.

i haven't read much of the above posts but could it be an air bound monoflow system?

Here's a crazy idea. What if the old over sized boiler was a cold start. Depending on how over sized it was it would need a long run time, store a bunch of heat and potentially satisfy the thermostat without short cycling.

Aren't they both cold start ? Or at least that is my assumption. I suppose if the system usage or the weather is different during use, but I would think @Ismellelephant may have noticed that.

"Finding honest heating companies on Cape Cod is particularly challenging due to systemic labor

That’s nation wide

To some extent that contractor is correct, the boiler is operating correctly for the situation it was put into.

So no matter how many people you ask, or hire you boiler is way too big and will short cycle. Even on a design day.

Here is a free load calc, fairly basic, but at least based on realistic numbers. Give it a try.

https://www.usboiler.net/heat-loss-calculator.html

Assuming the fin tube size, the average construction of the home, etc. that you supplied

It could be worse, the 1000 ft home could have a 77K heat load! Then you would have expensive problems keeping it warm :)

Suggestions have been made to time delay it, buffer tank it, tweak t stat cycles, etc. But you are treating a symptom, not the root problem.

I have a call in to a rep in the area that may have some contacts.

The small hydronic pros are often hard to find, most don't need to advertise. I'll PM you any suggestions he might have. But don't expect a much different answer.

As far as the old boiler.

I have seen boilers in the wild with a burner removed. That turns your 90K boiler into a 60K, for example.

Or orifices could have been downsized.

I doubt any boiler manufacturer would sign off on those modification however.

A tape measure is about all you need to do your own load calc. 7 simple steps shown below.

A calculator or slide rule.

Probably do this calculation with just a phone!

People tell me this calculator tends to calculate a bit on the high side.

There will be some assumptions as far insulation quality, air leaks (air change factor) , etc. But still better than all the guessing so far.

Take the load number and feet of fin tube to the person that sized and installed the boiler.

We should post a poll here, my guess is 28,296 btu/hr :) if it is 1000 sq feet of area.

Rarely gets below 26°F in that area, ASHRAE design temperature is 15°

https://www.usboiler.net/heat-loss-calculator.html

Yeah, I have a couple somewhere… what I DON'T have any more is the Friden desk calculating machine I had at one point… which could actually do square roots! Besides adding and subtracting and multiplying and dividing! It was quite the status symbol where I worked at the time. Of course, it took a while to do it…

Trivia… the computers on the Apollo command module and lunar modules each had a whole 16,000 bytes of memory… that's all.

And we got to the moon. And back. The right stuff!