Will a smaller boiler save oil?


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Old 03-27-09, 07:18 PM
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Will a smaller boiler save oil?

I have an old 2 family colonial in central Mass. Currently there is a weil mclain p468 boiler with a beckett burner. It has a rating of 155,000 BTUs. According to the slant fin heat loss calculator I have a heat loss of 105,000. If I get a smaller boiler is there a chance that it will use less oil? My house is a 2 family and the other boiler that heats the other side of the house is a weil mclain P368 and it uses almost half as much oil as the larger one does. The space on that side is 950 sq.ft and on my side it's 1200 sq.ft. If I replaced my P468 with a P368 or something similar in size and output would my oil useage go down by much? I know there are probably many more factors but I'm really just looking for a general opinion from a pro. Thanks
 
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Old 03-28-09, 08:16 AM
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The heat loss you did shows 105K for the WHOLE house? Sounds high to me... recheck your data and settings...

What is the BTU on the 368?

The first place to look for fuel saving is ALWAYS going to be improvements in the building envelope. Start in the attic and make sure that you have at least R40 insulation up there... leaky doors and windows should be weatherstripped or replaced, walls insulated, etc etc ...

Only when that is done should you consider replacing the boiler, if you don't, and replace the boiler first, then tighten up the house, your boiler will again be to big.
 
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Old 03-29-09, 07:36 PM
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105 heat loss IS wrong, I don't know where I messed up the calculations but I did them again and came up with 79. The house is actually very well insulated. The windows are single pane but they all have storm windows on them and I have put a lot of weatherstripping on the doors and such. I know there is a little more I can do in this area but for such an old house I am really surprised at how tight it is. The P368 that is on the other side of the house is 115,000 BTUs. I'm just not sure if I get another one just like it would I use that much less oil? for hot water I have a seperate hot water heater so thats not a factor.
 

Last edited by NJT; 04-01-09 at 09:09 PM. Reason: fixed typo...
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Old 03-30-09, 06:28 PM
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How many times I have heard the same thing. The heat loss was done and when someone here questions it and when redone is a lot lower. This is too big of a step to try to do and mess up, buy the boiler and end up still higher fuel bills, lower efficiency and more maintenance.
This is a 20 year investment and is too important to not properly input the information.
 
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Old 04-01-09, 07:32 PM
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I thought this was a forum where experts helped others. Instead it seems to be a place to make the the people looking for help look like idiots. I asked a basic question and gave all the information I had. I can't understand why I have 2 boilers side by side, heating different sides of the same house yet one uses half as much oil as the other. Is there anyone here that would have an "expert opinion" and tell me if "in theory" a smaller boiler, ie, one that puts out 115 BTUs vs 155 BTUs would use less oil to heat the same space? Sorry about the mistake I made in my heat loss calculation, It's not something I do every day like you guys do. And I know this is a 20 year investment, thats why I want as many OPINIONS as I can get before handing over $10,000 to the oil guy who doesn't care if it uses less or not.
 
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Old 04-01-09, 09:14 PM
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First of all, $10,000 sounds very high. Secondly, NJ Trooper was correct when he said sealing the house is first. Finally, I'm not a fan of Weil McClain. I don't think you will save enough money to make your investment worthwhile. You may find a burner with a better rating to replace the Beckett. That's about all I would do.
 
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Old 04-01-09, 09:21 PM
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I don't think anything was said that should make you feel like an idiot. All rbeck was saying was that we've seen this before... and that more care needs to be taken when doing the heat loss calc... so calm down... nobody is attacking you.

Unfortunately though, without being there to inspect the systems, it's going to be awfully difficult to give you a concrete answer to your dilemna.

If your heat loss is really 79K, and you've got two boilers installed that total over a quarter million BTU... then something is seriously messed up.

No, I doubt that you could cut your fuel bills that much by installing a marginally smaller boiler to replace the 468... there's only 40K difference between the two, and in the ultimate scheme of things, it's nothing... or very little.

Do both boilers have the same aquastat installed? Are both boilers set up to run as 'cold start' systems? Are you sure that the 468 doesn't have a 'triple' aquastat installed and is keeping itself warm 24/7?

What type of heat emitters are installed in the home? fin tube baseboard? cast iron radiators? If they are fin tube, or convector cabinets, when was the last time that the covers were removed and the dust bunnies vacuumed out of the fins? You might be amazed at the difference in heat output that this simple act can make. If they are clogged up with dust, and no heat is getting out, that boiler is going to have to work extra hard to heat the home.

I believe that you have two separate oil tanks, are they both underground? One under, and one above? Shudder the thought, but have you considered that you may be leaking oil? I'm a 'survivor' of such a case, so I pray that is not so...
 
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Old 04-02-09, 04:34 AM
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And are they both cleaned and tuned up regularly?

A slightly smaller boiler won't make that much difference. Maybe 5%. No way 50%.

The building loses heat that must be replaced. Look first at the building envelope and the myriad things Trooper said. Look last at a boiler replacement.
 
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Old 04-02-09, 01:59 PM
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Don't rule out temp differences between the 2 sides of the house. They may keep their side significantly cooler and if that happens a lot of your heat will go there.
 
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Old 04-02-09, 04:17 PM
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Cool

i guess i have a question about this what pressure are the boilers
running it might be as simple that the one is way to high
 
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Old 04-02-09, 05:34 PM
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How would the pressure (I assume you mean the water pressure in the system and not the fuel pump pressure?) affect the amount of fuel used?
 
 

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