Q on new boiler/HW system quote

MikeC555

My current boiler is an old, over sized beast; a 46 year old American Standard. The tankless coil wasn't up to the task since I've lived in the house (20 years) and service companies are afraid to touch it for fear of damaging the boiler (2 of the bolts are pretty rusted). After a year of poor DHW, I added an Aquabooster to the system and up until a few months ago, I had adequate DHW. It is now noticeably lacking temperature and I can also see a definite brown tinge when flowing into a white sink. So I think the coil is on it's last legs.

I did a Slant Fin heat loss calculation on my 1975 vintage wood frame, 2 story, 4 br, colonial style house (including finished basement) and for a total of 2,600 sq. ft, I come up with about 65 - 70K heat loss. I do have double pane windows and my assumptions were inside temp of 68 F, outside 0 F, 40 gallon indirect hot water. I also assume boiler water temp of 180 F and DHW temp of 140 F.

I received a few quotes, only one of which the guy mentioned heat load calculations and I showed him mine. He agreed my existing boiler is way over sized (150K BTU).

He quoted a Buderus G115-4, which he says is 109K BTU output and although maybe still a bit over-sized, I don't want to cut it too close. Burner is a Reillo F5 burner and Viessmann Vitocell 300-W EVIA42 indirect. I have 4 heating zones (4 zone valves, one circulator) and don't plan to change any of that since it has worked fine other than a couple of zone valve heads over the years.

One thing I am a bit confused about is the G115-4 boiler. I can't seem to find much on-line about the G115-4 or G115/4 and the on-line boiler places all mention the G115WS/4. The Bosch/Buderus website says the G115WS is the redesign based on the G115. This would imply they don't make the G115 anymore but the guy quoting it says it is still produced. It don't necessarily have to have the latest and greatest if the price is right but did the G115WS come out recently so suppliers still have stock of the older model? It seems strange they would continue to produce both unless the original had a significant cost advantage (and I can't find anyone offering the G115 on-line to compare). Any ideas what the deal is with this?

STEVEusaPA

That boiler is still too big based on your heat loss. Don’t add size for DHW.

EdTheHeaterMan

FYI Boilers are hard to find now. Don't delay If someone has a boiler available for you, then take it or wait until March or April. G115 or G115SW are both good. if it is still in the crate, the warranty starts when it is commissioned in your home. Just save the dated receipt for the final payment That is your proof of warranty commissioning.

There is an acceptable lower firing rate to safely downsize the boiler. The manufacturer has that information in the manual. I have purchased boilers that use 4 cast iron sections and have up to 3 different firing rates. So the 3 section or the 4 section will be just fine. Sometimes the high firing rate os the smaller boiler is greater than the Low firing rate of the larger boiler. If you find that your DHW does not recover fast enough, then just fire the boiler at the highest rate allowed. But as @STEVEusaPA said, you may be able to go smaller. (are you confident with you heat loss calc?)

I know of a larger contractor that has boilers "in stock" so they can install one without waiting for the supply house to deliver one. (the best price point was from a supplier that only delivered to his location once a week) Perhaps this contractor has a boiler from a few years ago that is ready to go.

Also don't think that the price ar SupplyHouse.com is your installed price or anywhere close to it. There are up to 100 other parts, fittings, supplies, oil filters, thermostats, and hydronic specialties that get added on the the cost of the job before the markup. Once that is done, the labor to remove the old one and install the new one is added. That total then gets overhead added. I used to tell my customers that the price on line is for the part(s) delivered. But I buy the better quality boilers and parts. "You see, my parts jump out of the box and install themselves and throw the old one away. I can give you a $5.00 discount if you don't want the one that throws the old one away."

Good luck with your project.

Respectfully Submitted.
Mr. Ed

HVACNUT

They are basically the same boiler. 
The G115/3 with Riello F3 will be more than enough. 

EBEBRATT-Ed

As others have mentioned don't oversize the boiler and don't add for domestic hot water load. But you should use 70 deg indoor for your calculations you will sell the house someday and 70 is standard not that it will change things much

MikeC555

Thanks Guys. I know the on-line pricing is just for the parts. I really just wanted to see a spec sheet for the G115/4 to be sure the output is the same as the WS model (or close). I've read a few things that suggest a Reillo F3 should used but I was spec'd an F5. They look pretty similar but I see the F3 maxes out at 0.95 gph firing rate while the F5 can go to 1.65. If the boiler is rated at around 100K, is better to down fire an F5 or upfire an F3? My old beast is down fired to 0.85 but with oil pressure turned up to 150 psi for better atomization (I think it worked out to 1.1 gph).

I'm pretty confident that I've made no major mistakes on my heat load calc. I was a bit fuzzy on how to handle the basement though. It does have baseboards installed but hardly ever turned on so it stays around 62 - 66 down there most of the time. In the Slant Fin Hydronic Explorer program, I treated the first floor as floor heated from below which it rarely is but it isn't exposed to anything near outdoor temps. Changing from heated to unheated but enclosed didn't make a big difference so I think my 65-70K is pretty good. I did plug in 70 indoor temp and it also made little difference.

Is the G115/G115WS a 4 section?