Planning a boiler replacement

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  #1  
Old 07-12-09, 09:17 PM
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Planning a boiler replacement

I've been planning on replacing my hot water boiler, which is old but runs fine, with a more efficient one and hopefully taking advantage the energy tax credit. I got a quote last week before realizing that I didn't really know enough what to ask (and before finding this site). I'm hoping to get a couple of answers and some advice before getting more quotes.

Old Boiler: 135000 BTU Janitrol from the 60s, which multiple people have said is probably about 60% efficient. It heats the house just fine, and seems to cycle off quite a bit even on the coldest days, so I assume it's got plenty of power to spare. The house is 1500 sf and 90 years old, but a lot of things have been tightened up on the house over the years.

The Quotes: 90000 BTU Slant Fin 84% efficient boiler, replacing the expansion tank, adding a few copper pipes and additional zoned shutoff valves, circulation pump, redoing some venting, $4850, plus $1000+ more for removing the old one by an abatement company.

- or -

120000 BTU Slant Fin 94% efficient boiler, and everything else above, $7300 (plus removal). This one would qualify for the tax credit, which was my hope, but thinking about it now, seems bizarrely oversized. It looks like this is maybe the smallest high efficiency boiler that Slant Fin makes, so perhaps that is the best this guy could offer. These quotes were a 15 minute appt where the guy looked at the old boiler and that was it.

Anyway, after reading a bunch of info here, I started doing a Heat Loss Calculation online based on my best guesses, and it's coming up at roughly 60k-65k BTU, but could be off a few thousand depending on the details. If I'm doing it right, that's isn't far off from what I'd expect given the existing boiler and would almost make sense with the 90000 BTU/84% efficient boiler quoted.

So my main question is just how bad is it to have an oversized boiler? In the example above, the high efficiency one costs only $1000 more ( $7300-4850-1500 tax credit). At 10% more efficient, I'd make that back at some point, unless it is going to wear out earlier or need more maintenance or just run inefficiently due to being sized wrong...how do I put a dollar figure on that? Even the regular efficiency one quoted seems oversized somewhat....a 80k BTU one could do it. But how exact can I expect to get? I'm sure I don't want accidentally go too small either. Right now, I'm hoping I can find a 70k-75k BTU high efficiency one for notably less than high efficiency quote I got that I can feel good about going with.

Is there anything else I am missing? I've read all the recommendations of a full home energy audit, but anything beyond that? Any good questions I should ask the next guy?
 
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  #2  
Old 07-13-09, 12:34 AM
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Location: Fairbanks Alaska
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Gas or oil (hope I didn't miss that). It is important because the boilers available are very different. I can guess that you are looking at gas because the 94% Slant Fin would be a gas boiler. Lucky for those with gas to burn because there are more high efficiency gas boilers on the market.
My area is mostly oil burning.
If you can name specific boiler models it will help because some companies make various style boilers.

Am I correct that you are in Minnisota? If so, you are in a similar climate to mine. Long cold winters.

You are on the right track with the energy audit. Often that gains you more than replacing the heating system. In your case I am sure that you need a new heating system for several reasons in addition to age, it is surely way too big and the old style that sits hot all the time. To understand what I mean, read the Energy Kinetics System literature. I don't sell those and there are many good choices, but they explain some things well, such as where the old boilers like yours waste energy and why AFUE ratings are only a partial part of the efficiency.
 
  #3  
Old 07-13-09, 04:48 AM
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Originally Posted by Craig in MN View Post

Old Boiler: 135000 BTU Janitrol from the 60s, which multiple people have said is probably about 60% efficient. It heats the house just fine, and seems to cycle off quite a bit even on the coldest days, so I assume it's got plenty of power to spare. The house is 1500 sf and 90 years old, but a lot of things have been tightened up on the house over the years.
I got a smile when you said plenty of power to spare. I had a 225K unit in my house so I, too, had enough power to spare to heat an entire apt building . Of course hanging wash in that utility room dried at record speed because that room was so toasty in winter. Now with my new boiler, you can set butter on top of it and it wont even start to melt i bet...sigh...

When i learned about low mass boilers with indirect hot water and ODR with a tekmar 260, i was sold and that's what i got. Love heating with cooler water during the shoulder seasons and cant wait to calculate the savings. No need to boil to 180 like my old coil unit and just keep getting burned with the hot water out of the faucet all winter either.

How did each contractor come up with the unit sizing? I had 2 oil companies come in and just measure my baseboards so crossed them off the list after the guys here told me that was bad. It's amazing what little these salesguys knew. They just want to sell oversized units to burn more oil or are incompetent to size a unit like that. Either way, bad news. When you call your next contractor, ask him how he will figure out how big a unit you need. If he says measure baseboards, i wouldnt even bother having him come out. Just my opinion.

You mentioned you tightened up the house so I'll 3rd the suggestion to get an energy audit and a good heat loss calculation. Then you can tell someone what size you need and let them quote you on it and you will be confident it's the right size. Also it's a good idea you are doing this in summer, i did it in fall/winter and it's not fun not having heat for 2 days and waiting for the job to even start.
 
  #4  
Old 07-13-09, 04:53 AM
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Originally Posted by Bilbo View Post
but they explain some things well, such as where the old boilers like yours waste energy and why AFUE ratings are only a partial part of the efficiency.
General comment to any newbies that may be reading this thread: I have learned, from this board, not to get hung up on efficiency numbers. You can have a 80% unit use less oil than a 90% unit if the latter is oversized. Sure you will be using 90% of the oil vs 80% but the volume used will be greater in the oversized so you really arent being very efficient.

just one of the many lessons i learned here.
 
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Old 07-13-09, 08:43 AM
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I'm in Minnesota, and using Natural Gas.


Originally Posted by luckydriver View Post
How did each contractor come up with the unit sizing? I had 2 oil companies come in and just measure my baseboards so crossed them off the list after the guys here told me that was bad. It's amazing what little these salesguys knew.
It was the same guy giving me two quotes. I asked for the high efficiency quote, and he probably wouldn't have given it to me otherwise...it wasn't like he was trying to sell me the higher end one. He just looked at the furnace and we talked for a few minutes. I assume he saw age and size of the old one and did some mental figuring. I have feeling his logic went: "the current one is 135k and 60% efficient and I only stock a few sizes of boilers and I didn't want to undersize it. The 75k BTU one might not quite cut it, so I'll quote the next bigger one....90k BTU." That might end up being the best he could offer, for all I know.


Originally Posted by luckydriver View Post
General comment to any newbies that may be reading this thread: I have learned, from this board, not to get hung up on efficiency numbers. You can have a 80% unit use less oil than a 90% unit if the latter is oversized. Sure you will be using 90% of the oil vs 80% but the volume used will be greater in the oversized so you really arent being very efficient.
Thanks for this. That is really what I wanted to know. I've read a few things hear that said oversizing ends up being inefficient, but I wasn't sure if it would be inefficient enough to overcome the other savings. The only reason I care about the efficiency numbers is because of the limits of the energy tax credit. If Uncle Sam wants to help me buy a new boiler, I want to take advantage if I can....but I'm not going to waste that money getting a boiler that is going to be less efficient in the long run.
 
  #6  
Old 07-13-09, 10:02 AM
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Get a full energy audit. Best ~$200-300 you will spend. That should include a blower door test (for infiltration - leakiness of house) and thermal IR imagery (for heat loss -- continuity and extent of insulation).

That audit should also include a heat loss calculation to compare against yours and any contractors.

THE best place to make the home more efficient is the building envelope. There are good tax credits on everything -- insulation, windows, doors, garage doors, you name it. Building envelope improvement has the best and shortest payback.

Once you get the heat loss, and recalculate the heat loss for the new building envelope improvements, THEN you are ready to size the boiler to the heat load. If necessary, you can also go ahead with a smaller boiler while you are making the building envelope improvements. Even over the course of a couple heating seasons.

The slantfin 93-94% offering is likely the Bobcat:
http://slantfin.com/documents/536.pdf

slantfin has their own heat exchanger design. Haven't heard much about it. The picture in the literature looks like it might be a real chore to clean.

Keep getting estimates, gaining knowledge, and don't be in a rush.

New boiler time is also a good time to think about how you heat your domestic hot water. A modern, modulating/condensing boiler is about the most efficient way to heat domestic water. If you have a tired old water heater, think about an indirect water heater run off the boiler.
 
  #7  
Old 07-13-09, 10:42 AM
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the logic and figuring guy just looking at the boiler makes me say with almost certainty you dont want that guy doing your job. (i guess he could be good at installs, just not know how to size though) Sure it takes over an hour to measure a house and figure out the heat loss but it would worry me if he cant do something 'simple' as that, do you really want him piping out your new 5K + unit correctly? Plus it's summer and he has more time than in winter so it's not like he's under the gun with no heat calls. Thats just my take on that. I'm very jaded by the 2 guys that came to my house as you can tell.

Originally Posted by xiphias View Post
Get a full energy audit. Best ~$200-300 you will spend. That should include a blower door test (for infiltration - leakiness of house) and thermal IR imagery (for heat loss -- continuity and extent of insulation).

If you have a tired old water heater, think about an indirect water heater run off the boiler.
2nd that audit!. Craig if you follow the guy around you will be amazed where air comes in. Put your hand all over the place while he's doing it. It was pretty cool..literally... to see where air snuck in. I had no idea that all my woodwork around my doors and windows was leaking so bad. The windows and doors themselves werent bad at all! Also lightswitches and outlets are letting tons of air in here.

Also, with my old short cycling monster, 67 was my overnight temp and 68 or 69 was comfortable for occupied times. Now 65 is my overnight and pretty much what it's set at all the time now with just a 5 hour 'burst' to 67 each night when i come home from work. But i feel warmer at 65 now vs 67 before. hard to explain but thats how much caulking up the leaking woodwork helped in my case. I'm sure my new boiler had something to do with the more 'regular' heat too. I notice the baseboards are much cooler but much more steadier of a heat vs the blast of 180 degree water from the old unit then it doing a bunch of short cycling to heat up the house (the water got refired ever 10 or 15 degree drop vs now my tekmar 260 runs the differential which can be up to 40 degrees and longer cycles are better for efficiency!). I'm sure there are more technical terms for all this but basically cooler is warmer now

the other thing about the indirect mentioned above is it's so well insulated that it wont run all day if no one is home using water. I've witnessed this on weekends. Or even if you just use maybe 5-10 gallons out of a 40 gallon tank it wont turn on. I would be 'scared' of running hot water with my old coil because i knew the moment i turned it on, i had to wait about 3 min for hot water to get to the sink sometimes and then the boiler kicked on immediately. Disgusting to heat up to 180 for continual heating of that 5 or so gallons in the unit when i maybe needed just 3-4 gallons. but id get all 225K of oil used up just for 'nothing' really. Then of course even if you go away the thing heats up that water continually to 180 even with zero usage. Pure waste! I feel so bad all these years i wasted.

with the indirect the boiler, it heats up the 40 gallons of domestic and you can use 'some' hot water without the thing firing up. I've washed a few pots and let the water run for minutes and the boiler never fired. Also i must have had a blockage because i get hot water in 1/2 the time as before. That will save probably 2 -4 gallons of water per use vs my old blocked coil setup.
 
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