Re: Low mass boilers...what do you know about them?
luckydriver wrote:fishin wrote:
The $6,500+ up-front cost inhibits most people. Plus, most people don't have a 60 year old system to replace. The gains wouldn't be the same if you were replacing a 10 year old system.
while i understand the sales guy was hedging his bet, will you stick your neck and and guesstimate what i may be saving by getting something new? 1300/gal year now.
A typical furnace replacement for a 30 year old unit will have a payback period of between 6 and 10 years. It varies by how much heating you do and what you pay for heating oil. You mention below that your burner tech has been listing your current unit at ~75%. If you the new unit you are looking at is a 90% unit then you should use roughly 15% less oil.
1300 gallons at $4.50/gal (current price in my area) = $5,850.00/year.
If you reduce that by 15% (90% minus 75%) then you are at:
1105 gallons at $4.50/gal = $4,972.00/year.
That's a reduction of $878/year. If it's $6,500 to replace it then you have a payback period of 7.4 years. (That could be a few months high depending on your domestic hot water use) If prices continue going up then the payback period will be shorter. If they go down then it'll be longer...
Quote:Quote:Your current hot water tank stores your domestic hot water. The new system would use a 30 gallon storage tank for the heated water to be used in the heating loops (i.e. radiators). They'd set it up so that the furnace heats 30+ gallons of water to the preset temp for the radiators. If the thermostat tells the system it needs heat then the circulating pump kicks on and distributes the already heated water from the 30 gallon tank instead of firing the burner like your current furnace does. The new burner only kicks on when there is a demand + when the water in the loops is below the preset temp.
wow i totally misunderstood him. I thought the 30 gal was for the domestic and the 5 gal was for the heat. Ok you said the 30 gal was used for the baseboards. So during winter even if the 30 gal tank gets cold, it wont turn on unless heat is called for right? That sounds like huge savings to me
Right, it won't turn on unless the thermostat kicks it on. But there are trade-offs here. Your current setup doesn't have that storage tank. The new one will have to heat that 30 gallons of water in the tank as well as what is circulating to the radiatiors. It is much more efficent than your current system but not quite perfect. (There are always those damned trade-offs! Arrgh!
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Quote:And year round i'm saving not heating the domestic water except on demand. Again that sounds like savings.
True. Not as efficent as a stand alone on-demand water heater but you'd need natural gas or propane to go that route...
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I don't fully understand what you are trying to do with your math here but I don't think it really matters. (Nozzle size is only one of several factors that goes into figuring out how much you might save.)
ok but isnt the gallons per hour a 'true' number? So in theory if the new one did run as long as the old one, wouldnt i really be saving .5 gal/hour? But i sure would hope the new one ran much much less time. Do you think there's a circumstance where this new one would run longer?
It's a true number but it is only one of several true numbers. I could reduce the nozzle size in a furnace by 50% without doing anything else but it isn't going to generate a savings. It would just mean that the furnace would burn twice as long to do it's job at the same level. Think of it as a water pipe filling a bucket. if I need 20 gallons of water I can use a 20 gallon bucket and a 3/4 water pipe and it might take 1 minute to fill the bucket. Of I can use teh same bucket and a 1/2" pipe. I'll still get 20 gallons in the end but it will take longer to fill it from the 1/2" pipe.
The AFCU factors all of those together for you. That's why it's a more helpful number to look at. To use nozzle size you'd also need to know exactly how many hours the furnace will actually run, how hot the fire it produces is, the size of the firebox, heat transfer properties of the materials used in construction, ambient daily air temps, etc...
There are a lot of circumstances where a new unit would run more - not all of them are bad either.
This is where you start getting into the pros/cons of a low mass furnace.
In your old furnace you have a huge cast iron housing. That's mass - big heavy stuff = mass.
Mass retains heat. Your furnace kicks on and all that cast iron heats up. Water runs through the cast iron jacket and heat transfers from the iron to the water. The water then gets pumped to the radiators. But it takes quite a bit of oil to burn long enough for all that mass to heat up. The advantage of a high-mass furnace is that the thermostat can call for heat and if the furnace is still hot it doesn't have to fire up again. The burner only kicks on when the water temp drops below a preset temp but it will maintain that water temp all the time - even if there is no demand for it. The system has to do this to keep itself together. Heating cast iron (or steel) causes it to expand. If the furnace heats up and then cools off often enough the interal gaskets will fail and the water jacket will start leaking - that's a pretty major repair and not something you want to have to do on a cold winter night. And the high mass furnace has to do this year round. Even in the summer when you are only using it for domestic hot water it has to fire to keep itself heated up several times a day. That's a waste and you are paying for it.
In a low mass system the water
is the mass. The furnace is built out of lightweight materials - often ceramics. They don't retain heat well but the trade-off is that they heat up quickly. So the furnace kicks on and ignites and water starts heating to distribution temps within minutes. And it heats some extra (that 30 gallon tank!). Water does a pretty good job of holding heat (ever notice how a lake or pool will seem warm in the evenings after the sun has gone down? The land cools quickly but the water retains the heat it absorbed during the day longer!) so instead of relying on the mass of the furnace to heat water there is a large storage tank doing that job. The low mass furnaces are made of materials designed to expand and contract often so you don't have the issues of gaskets leaking and such. That means the furnace can go cold if there isn't any demand without any problems. In theory, it should fire less often - especially in the summer when it only needs to fire up to heat domestic hot water when you turn on a faucet.
IMO, the low mass systems lose some of their attraction if you have several heating zones and are living in a region with short summers.
Let's say you have a very large house with 4 heating zones. The thermostat in zone 1 kicks on and tells the furance it needs heat. So the furnace does it's thing and heats the circulating water for zone 1 and the 30 gallon tank.
20 minutes later zone 2 kicks in and decides it wants to be heated. So it's circulating pump kicks on and the water in the tank circulates to heat that zone. Now you are out of hot water. If zone 3 or 4 kick on the furnace has to light up and heat more water.
In the older high-mass designs the cast iron furnace would still retain enough heat to heat the water circulating from zone 3 or 4 so it would fire less often.
But there aren't many houses that have more than 2 zones and there are ways to deal with that with a low mass furnace too (i.e. bigger storage tanks, combining zones, etc...). I'm assuming that your sales guy surveyed your current system and calculated the total water volume for all the zones when he spec'd the 30 gallon tank.
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So simple calculations should let you figure out that if you are going from say... a 60% efficiency furnace to a 90% efficiency model your oil consumption should drop by the 30% difference. Someone would just have to look at how much heating oil they use each year to figure out how much that would save them.
the numbers they write down on the paper each year indicate anywhere from 75 to a high of 82 percent years ago. however i dont know if that is accurate. I think they got it by putting something in the hole in the chimney pipe but am not sure. But like you said, this probably is closer to the 60's in 'real life'. I guess it's true there is no way i WONT save, it's just how long is the payback for 6500
*nods* They are measuring the burn effiency by looking at the exhaust gasses. That's as close as you are going to get outiside of the lab.
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Every furnce sold since 1987 has an "AFUE rating". Ask what the rating is for this new furnace and then have someone test your old system (any oil burner tech should be able to do that test for under $100. - they won't be able to recreate the lab conditions but they can come close enough...) Then you'll have real numbers to look at based on something other than a salesman's pitch.
NOTE: Those numbers aren't going to be a perfect predictor. They'll only tell you the differences in the furnaces themselves. The rest of your heating system (i.e. radiators, distribution piping, etc...) has an effect on overall efficiency too!
well nothing i can do about the pipes etc. But is the test the tech does every year when he cleans the burner any good or is your 100 dollar test something more extensive (i'm guessing yes).
Nope. That's the test. It's a rough estimate but as good as it gets once the furnace has been installed.
But Ill take your figure to be conservative. 878 is fantastic. See i have to decide in the next few months to move or refi. If i refi i am trying to get money out to buy a new furnace because i cant afford 5K next year for heat. 
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