Need help deciding boiler replacement size. 3 different models by 3 different contractors

mikenichols401

i need to replace an old oil fired boiler which has a heating capacity of around 206k and water BTU/hr of 179k

The boiler has a 50 gallon indirect gallon tank.

There are 5 zones, house is around 3200 sq feet with lots of windows from the mid 1980s.

I have around 190 feet in baseboard heating, and a few kickplate and in-wall hydronic fan type heaters.

It would cost a small fortune to replace all the windows, they are andersen but some are huge floor to ceiling panes that are 10-15+ feet high.

I had one contractor quote a buderus 215/5
Another quoted a buderus 215/3
A third recommended a buderus 115 (didn't give the exact model)

The 115 guy claims that the 215 is oversized and the 115 would be fine.

I am hesitant given the 115 has less BTU/hr than the current system.

A 215/5 gives 207k but
215/3 gives 117k
where the 115 maxes out at 136k on the highest end model

I'm located in southern new england.

I did ask the guy who quoted a 115 to give me an updated quote to say how much more it would be to get a 215 model.

I haven't done a heat loss calculator, but rough btu calculators seem to indicate that even the higher end 115 or the 215/3 is too low BTU for the space.

I was wondering if anyone could offer some advice, naturally i don't want to oversize too much but in general i have been happy with my existing setup, we never have issues with not enough hot water even with people taking back to back showers and the heat has been fine.

Thank you.

Hot_water_fan

How much oil do you use per year? 

EdTheHeaterMan

The accurate Load Calculation is the first step in any project where you are installing a replacement boiler. Get that done by the contractor that is doing the job or by an independent engineer. You don't want to buy too much heater. But you don't want to get one that is too small.

I am a big fan of Buderus Boilers especially for Oil Heat. Have one in my own house. But if you have a dealer for Energy Kinetics system 2000 near by, you might want to get a quote from them. That will reduce your fuel usage more that the cast iron boilers will. And that dealer will do the load calculation. but the price might be a little higher.

mikenichols401

Hot_water_fan said:

How much oil do you use per year? 

I use 950 gallons of oil a year currently.
That is with running a wood stove almost nightly from november until march whenever it will be below 40 degrees at night.

It doesn't seem like any of the quotes did a real load calculation and were either going by prior experience or specing it from the size of the existing unit.

The one that quoted the 215/3 had me measure the length of all the baseboards, neither of the other two asked for that information.

EdTheHeaterMan

I believe that a contractor that is asking a home owner to do their job for them in order to offer a quote, needs to get a job in politics, not in HVAC.
Next thing you will be getting out your tools to install the thing.
Call the EK Dealer for your area!

Hot_water_fan

https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler

This is a quick way to do it. It would be tricky with your wood usage though. You could try oil only for a cycle, or keep close track of your wood usage as well. 

FYI 190LNFT of baseboard is about 114k Btu, not sure what your other emitters can output. Usually radiation is oversized (you’ll notice if it isn’t), so that should be your ceiling. 

EdTheHeaterMan

Think of it like this. If your home was built in the 1980s, the boiler you have was sized in the 1980s based on the home construction standards of the 1980s. Many boilers were oversized back then.

Have you added anything to your home that would make it use less fuel? Added attic insulation? Replaced any of the windows? Built any additions that would increase the load? Converted a garage to living space? All the changes from then to now will have an effect on the size of the heater you need. Without a proper load calculation, you are just guessing. Case in point, you have 3 different guesses in front of you right now.

Jamie Hall

You have three approaches to determining size and, fortunately, they are independent. The most reliable would be an heating load determination, known as Manual J. A contractor should be able to do that -- but it would be reasonable for them to charge for it. The second is the fuel usage, but in your situation with the wood stove going, I'm afraid that would be quite inaccurate. The third may be your best bet, and that is to consider the amount of existing radiation in the house. As @Hot_water_fan noted, the installed baseboard is probably good for around 120,000 BTUh, but you should also add in the other miscellaneous heaters you have installed. That total will give you the maximum amount of power the radiation can use, and thus the maximum net output you should install.

ethicalpaul

I am hesitant given the 115 has less BTU/hr than the current system.

Of everything you said, this is the most confusing to me. Is your current boiler running all day on the coldest day? If not, why are you worried about getting one smaller than your current one?

EBEBRATT-Ed

Going by the length of finned baseboard is a safe bet. It would be rare for someone to install too much baseboard. 190 feet x 550BTU/foot=104,500net water rating

@mikenichols401 are you forced to do this now because your old boiler is failing? It would be a lot better to wait until summer if you can. You could take more time and do a heat loss and pick the right contractor.

Rush jobs are always more $$$$ and never as good quality wise. You only have 2 months to go.

hot_rod

I'd add the kickspace heater at maybe 15,000 to the 104,500 that the fin tube can move and call it a
120,000 heat load the the emitters can move. No need to size larger that that.

JayMcCay

mikenichols401@ A lot of information to considered...Sizing a boiler replacement based on existing equipment is not a good option it leads to over sizing and wasted energy with your new equipment.
Please give me a call at 908 328-7154 be happy to go into more detail with you.

Regards
Jay