Short Cycling Boiler Replacement - Advice Needed

Berkshire01230

I am looking for some feedback on a proposed boiler replacement by my heating company. I will try to make this as short as possible.

Some background:

Buderus G115WS-5 with Riello burner was installed by a local heating company in Oct 2022. They also installed a Burnham AL50SL indirect hot water heater. There are 5 heating zones in my house plus the zone for the indirect hot water heater. The zone valves are Honeywell and it has a Grundfos Alfa circulator. My house is located in Western Massachusetts, in the Berkshires, and is about 2100 sq ft. This is an oil, hot water baseboard heating system.

The original heating company was bought out by a larger firm in New England about 1.5 years ago. New service tech seems more experienced and didn't like some of the piping and the aqua stat that was originally installed. They re-piped the water feed to a tee above expansion tank and added a micro bubbler - made sense to me as I read Dan's book. They also replaced the aqua stat to a Hydrostat 3250, which includes a low water cutoff. Prior to these changes my cycles times were 5-8 mins, which I know isn't necessarily ideal and I mentioned a number of times to both heating firms that it was my opinion that they installed an over-sized boiler.

Although the cycle times have never been optimal, they are now consistently 2-3 mins after these changes were implemented. I had the service tech back here today and he tried adjusting some of the Hydrostat settings and nothing helped to increase the cycle times.

The original aquastat had a temp. differential of 20 deg., whereas this new Hydrostat appears to have a preset differential of 10 deg., so it is my opinion that this is causing the decrease in cycle times. Makes sense, a 20 deg drop in temp takes longer to hit the max temp than a 10 deg drop.

After a discussion with the manager, who stated there was nothing else they could do to increase the cycles times, I said yes there is - replace the boiler.

Low and behold, they came back to me and agreed that the Buderus was over sized and offered to swap out the Buderus with a PurePro P4 Water Boiler Trio, 4-section at no $$ to me.

Here are my questions:

1. Never heard of a PurePro and I am wondering how this compares to the Buderus G115. Last thing I want is a lower quality system than what I originally paid for. Heating firm said the PurePro is more energy efficient than Buderus and that they install way more. Hmm?
2. I have questions on how the tech came to the conclusion that the 4 section PurePro is the right size for my house. The manager said he recommended a 4 section over a 3 section because of the indirect hot water heater. I have read that you should not take the indirect into consideration. Is this accurate? Don't want the same short cycling issue. No heat loss calc was performed and he didn't even look at how much baseboard I have. As I mentioned, 2100 sq. ft. house, built in 1988 with 2x6 framed exterior walls, double pane windows and doors.
3. Zones: the original owners had 5 zones installed and some are small.
   1. Living room, kitchen, dining area zone - 29.4 ft. of baseboard
   2. 1st floor bedroom - 8.6 ft of baseboard
   3. Master bedroom and bathroom - 16.3 ft of baseboard
   4. 2nd floor bedrooms (2) & bathroom - 18.4 ft of baseboard
   5. Finished portion of basement - 21.2 ft f baseboard
   6. This equates to roughly 94 ft of baseboard total
4. Am I better off having a buffer tank installed because of these small zones and keeping the Buderus?

I appreciate the feedback. Thank you.

Hot_water_fan

Buffer tank before a new boiler. But do you even need to do that? Could you combine zones? Or just live with the short cycling?

jesmed1

"No heat loss calc was performed…"

The saddest 6 words spoken after any expensive boiler install. With insulated 2x6 walls and double-pane windows in the Berkshires, your design day heat load is probably well under 20 BTU/hr/sq ft, so probably less than 40,000 BTU/hr for the entire house.

As a sanity check, 93 feet of baseboard emitting 500 BTU/hr/ft will give you 46,500 BTU/hr, but that's probably more than you need, so you can probably heat the house comfortably on a design day with water that's not quite so hot.

A Buderus G115/5 with a DOE output of 136,000 BTU/hr is probably 3x or more what you need for heat. Of course there's also the DHW load, but even with that, the G115/5 is still overkill.

Just for reference, we live in a 4-unit condo building in Boston that has 6 residents and one 80,000 BTU/hr water heater that's perfectly adequate for all of us. So your G115/5 could probably keep your house heated on a design day with 40,000 BTU/hr or less, while continuously sending 80,000+ BTU/hr to DHW to keep making enough hot water for 6 people.

I am not a pro, just a homeowner/engineer. So I will leave it to the pros to recommend a solution. But if it were me, I'd take advantage of the situation and ask the heating company to give me a buffer tank instead, which would solve the many-zone/short cycling problem that you'll still have even with a smaller boiler.

hot_rod

93’ X 550 =51,500 btu/ hr that the fin tube can transfer. Can the replace the Buderus with a 75- 80,000 BTU/hr boiler?

That a start, then maybe combine a few zones

EdTheHeaterMan

Trio is the brand of boiler that is made in Boyertown PA at the Boyertown furnace co.  It is sold exclusively by the Supply House chain F.W. Webb.  The boiler cast iron sections have a limited lifetime warranty to the original owner in the original location.  All the other parts have an industry  standard 1 year warranty.  

The 5 section Budreus boiler can be fired up to 161,000 input with a net rating as low as 118,000 (NET is the size you use for matching  the heat loss of the home) The Trio has a maximum firing rate of 140,000 BTU input with a NET as low as 101,000 BTU  that is only 15% smaller or about 85% of the existing boiler size.  If your boiler is short cycling at 2 to 3 minutes on with about the same off times that would mean that the boiler is 200% larger than it needs to be. A 15% reduction is a drop in the bucket when you look at those numbers.   If the 2 - 3 minute run times with longer than 3 minute off times is the case, then the boiler is even more than 200% oversized.

As far as an indirect water heater is concerned, you do not need to over size based on the hot water usage unless you have a very high DHW demand.  Usually the 40 gallon tank can handle the standard hot water needs of the home with a 105,000 BTU input and a 75,000 BTU NET.  

You are not getting a lower quality boiler from Trio since most of the components are the same from boiler to boiler.  The Cast Iron block is well made in the USA.  The Buderus cast iron is made in Germany with a little more silicone making it less likely to crack.  But that is not usually a concern if the boiler is properly maintained.  

I would lobby for the 3 section after an actual Manual J load calculation is performed to be sure that the 105,000 BTU boiler with a 75,000 NET will work for you.  With only 94 feet of baseboard heating your home comfortably, you don't need anymore than about 55,000 to 60,000 NET BTU. The 3 section should work for you.

EBEBRATT-Ed

Does anyone else think its odd that they will replace the boiler for free? I still would do a heat loss, more boiler than you need means more fuel you will burn.

Your baseboard if you listed all of it will only provide 52,000 btu. And you don't add anything for domestic hot water.

The PROP-3 will do 79,000 output and is plenty large enough.

HydronicMike

https://forum.heatinghelp.com/discussion/comment/1879876#Comment_1879876

It wouldn’t surprise me if this is a larger company. They probably get a good price on the trio, and they have a home to resell the Buderus to.

hot_rod

The fin tube connected to the boiler will establish the boilers operating condition

If it has heated fine in the past with 93’ of fin tube the load calc will not tell you much more than possibly the ability to run lower SWT

But with a cast boiler you can’t go much below 150 or so regardless

Any boiler with around a 60,000 output seems to be adequate and matches the fin tube capacity almost perfectly

the multiple and micro zone is what drives decisions like a mod con type boiler😗

Hot_water_fan

@hot_rod oil can be found in 60?

hot_rod

keep in mind also, 80% of the heating season you are below design conditions. So even if you got it sized perfectly for design day, most of the season it is sill oversized and will cycle accordingly

hot_rod

https://forum.heatinghelp.com/discussion/comment/1879882#Comment_1879882

Steamhead suggested this MPO is about the smallest, so the 64k output gets closest

Berkshire01230

Thanks to everyone for the replies and feedback.

@EBEBRATT-Ed - I have thought a lot about why they are willing to replace it for free, because I never expected that to happen without some legal threats. They didn't size it or install it, so no egos or finger pointing about who made mistakes. The company they acquired made the mistakes. The manager told me that the service tech for the new company admitted that he would never have installed this for my house. I also believe they truly want to do right by me and have me stop pestering them. They also get to take back the Buderus and sell it to someone else.

@EdTheHeaterMan - thanks for your feedback on the Trio PurePro. You are spot on, they are getting it from F.W. Webb. They are a large company and I would think that they get volume discount pricing from Webb. They also told me this morning that it would contain the Carlin burner. Any thoughts on this burner as I have never heard of it. The other choices are Riello or Beckett. The Riello with the Buderus is very loud and I can literally hear it fire from my 2nd floor bedroom - doesn't make for a great night of sleeping. Someone asked if I can just live with the Buderus. Well, my living room is also directly above it and hearing it fire up 8-9 times an hour when watching TV is about to drive me insane.

Any thoughts on the Beckett vs Carlin? My guess is they want to go with Carlin because that is what they are most familiar with and stock parts for it.

Also, I wouldn't consider our demand for DHW to be very high. I have a 50 gallon tank. This is a second home and 90% of the time when we are here it is just me and my wife. We only run the dishwasher every 2-3 days and do laundry only occasionally. The other 10% is when we have family or friends staying with us. Would you agree that this is a low demand for DHW?

I have asked for a manual j load calculation - let's see where that goes. Although, based on the information here it would most likely confirm that a 3 section boiler would be sufficient.