Boiler replacement size.

Shadowdoc

Greetings…I’m gonna try to keep a complicated topic as simple as possible. I know it’s not that simple at all. Sorry. 

I’m looking to replace a gas boiler that heats 2 floors of a fellowship hall I have converted into living space. I have not added or removed anything structurally (walls etc). 

Current situation is 2 levels / 2 zones. Current boiler is 300,000btu input/240,000 out. Installed in 1989. Has heated the space fine. There is a leak in the exchanger, so I want to replace it. Also due to age and deterioration. 

Baseboard elements of 105 linear feet 3/4” copper upstairs for ~3200 square feet of mostly open loft type space with 11’ ceilings  and 155’ 3/4” downstairs for ~3200 square feet of space separated into 10 rooms 9’ ceilings. 

One suggestion is  to replace with same size boiler ~300,000 (commercial boiler) and never took ANY type of  measurements.

One suggestion is to replace with a residential boiler utilizing 265’ baseboard element X 500btu/foot meaning ~130K btu, but a little larger due to efficiency. 

I know about heat loss calculations, square ft calc and volume but none of that has been done. Assuming that’s all the info available….thoughts????

Location is middle of NY. Thermosat settings are always between 66-70 almost invariably. 68 average during the day and 66 at night. 

Any insight would be appreciated with just the info I have at the moment. Thanks in advance. 

Hot_water_fan

A boiler cannot emit more heat than its radiation. No sense exceeding that. 

bburd

I would check very carefully what the average water temperature is in that existing system before using the radiation to size the boiler. Or just bump up to the 200° AWT figure on the radiation chart, so perhaps closer to 700 BTU per linear foot. Don't go by the limit control setting, they're not necessarily accurate.

Are you sure that is standard and not high output baseboard?

But If I owned the building I would calculate the heat loss.

EBEBRATT-Ed

@Shadowdoc

@Hot_water_fan said no sense putting in a larger boiler than the radiation can heat. 265' x 550btu/foot =145750 x 1.15 piping and pick up factor=167,612.

If the boiler is 83% efficiency you need a boiler with an input of around 200,000 btu.

It would be better to do a heat loss calculation first.

EdTheHeaterMan

Sounds like you need to find another contractor that will do the work to get the actual load calculation. Someone with the knowledge to do it right the first time.

I offered two different Churches a good, better, best option with the boiler replacement and one nunnery the same deal. (of course they were customized for each job.)

Good = A single commercial boiler sized to the needs of the building.
Better = Two residential boilers to operate in stages as needed.
Best = Same a #2 with outdoor reset controls for better comfort controls

Church #1 selected the single commercial boiler with the optional oil/gas burner
Church# 2 went with 2 residential boilers
The nunnery went with the two boiler idea, BUT I was convinced that the boiler job was way oversized, and they were worried that my calculation was wrong. So I offered to install the boiler job in stages. I installed only one of the two boilers and installed tees for the second boiler stage 2 of the job. After 3 winters on not needing any more heat than the first boiler proviced, We never finished the job with stage 2 </i

So my suggestion is to get yourself a bid on a two residential boiler job, Then find out if you actually need the second boiler before you pay for more capacity than you need.


Chances are that a 100K boiler will do you just fine. Will be more efficient than a 130K boiler, and only if you actually need it, install the additional boiler of perhaps 50K or 45K. then you can stage them for the smaller boiler to heat in the spring and fall, then transfer to the 100k for the rest of the winter, and only when you need more than 100K will you need to bring on both at the same time.

Shadowdoc

Thanks everyone. I had 2 ‘opinions’ as I mentioned above. Waiting for final estimates. 

I asked about possibly using 2 residential boilers, 1 for up and 1 for down. Naive as I am. 

#1 said not a good idea. Too costly until they told me there is a looong wait for a 300k. So 2 smaller ones may be the quickest option. 

#2 said residential would work fine based on linear footage would bump up a little in size in case I wanted to add a little more elements in the basement where boiler is located if I was worried about freeze. But it never gets that cold in that part of the building which is under the ‘chapel’ and has no running water in it. Plus it has never got below freezing in there. Dirt floor basement. 

Also, which I just checked, the hall (aka bingo hall where I live in) has 60’ of high output elements but the remaining are all standard throughout. Never knew that.

PS. Current boiler is working but has a leak in the exchange so I want to replace it so that in the middle of January when it’s 5° outside, it doesn’t become an emergency situation, and I have no heat.

Thanks again for all the input.