Boiler Replacement Recommendations

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Old 06-16-11, 10:36 AM
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Boiler Replacement Recommendations

Hello,
I am replacing my aged oil fired boiler. I am looking at a 90%+ condensing boiler. Middle group brick town-home in Baltimore. Looking for feed back on the following brands and other suggestions: Weil-McLain, Biasi, Slant Fin, Buderus, Crown
Sizing is estimated at 90K input BTUs.

Thanks, Lou
 
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Old 06-16-11, 06:16 PM
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First, the sizing. Do, or have done, a heat loss calculation. It is virtually impossible that a middle home in your climate needs 90k BTU/hr. Unless maybe you leave all the windows and doors open all winter.... Your actual heat loss might really be a third of that. But you won't know til the calc is done.

Second, will the boiler also be used to make domestic hot water using an indirect water heater? This does not generally affect sizing, but can affect settings for the boiler control (i.e., 'DHW priority') which allows the boiler to direct full output to the boiler for a few minutes before returning to space heating

As to the brands, I would be less concerned with brand than with quality of the installer. Shop them. Get a bunch of quotes. See who will do a heat loss calculation. The good guys might charge you for it, but will often credit the charge if hired for the job. Four out of five might be knuckleheads.

My preference in modcon boilers are those with a stainless steel heat exchanger, and preferably one with open passages rather than highly restrictive design that requires additional pumping. The W-M and Buderus are aluminum. The others, I don't remember offhand.

I would check into the Triangle Tube Prestige Solo (the 60 would be plenty), or the TT Prestige Excellence, which has an integrated indirect water heater. You might also look at the new Lochinvar Fire Tube Knight (http://www.knightheatingboiler.com/knight/pdf/WHN.pdf) which is similar in design.
 
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Old 06-16-11, 08:03 PM
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I did the heat loss calculation and came up with 16,785 BTU/hr loss. This appears to convert to 45,000 BTU output according to the slant fin program. Not quite sure if that is correct. I am going with a stand alone water heater. The other question I have is the old unit had enough waste heat to warm the basement, I may have to add a heat source there to make up for that....
I'll have a look at the boilers you mentioned.

Thanks,

Lou
 
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Old 06-17-11, 03:22 PM
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Bearing in mind you are in the middle of the row and code does not allow you to vent under a deck. If you vent on a public sidewalk you must be 7' above the sidewalk.
Is this doable?
 
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Old 06-17-11, 03:52 PM
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17k BTU/hr loss requires a boiler with 17k output.... Maybe the program is steering you to their smallest boiler.

How many square feet is the home?

What kind of heat emitters? Fin-tube baseboard? Cast iron radiators? Other?

17k BTU/hr is at the low end of most all of the smallest modcon's output range.

There are other options for hydronic heat system source for that low of a heat loss, but it's been awhile since I've looked at them.
 
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Old 06-17-11, 04:15 PM
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Lou, you mentioned that your aging boiler is oil fired... it seems that the guys might be recommending gas fired appliances... are you converting to gas for the boiler?
 
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Old 06-17-11, 04:33 PM
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I have plenty of room to vent, I have a decent back yard so no concerns there.
The home is 1250 SF, not including the finished basement.
Yes, I am saying good bye to the oil monkey.
In wall fin convectors.
I really think that I am in the 75K-90K range as far as sizing goes.

Lou
 
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Old 06-17-11, 07:44 PM
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If that heat loss is accurate I would choose a boiler that you can turn the fan speed down and only fire at minimum.
The other option would to be install a 30k chimney vented cast iron boiler.
 
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Old 06-18-11, 07:00 PM
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You are absolutely NOT in the 75-90k range for sizing. No way, no how. Not in a middle townhome unit of 1250 sf.

A heat loss of 17k BTU/hr at design (in Baltimore, around 13-15F) for 1250 sf is about 14 BTU/hr/sf. That's about right for a house with two warm (not exposed) sidewalls.

If you were really in the 75-90k range, that would be a heat loss of 60-72 BTU/hr/sf. An uninsulated brick house on a windy hill in Vermont isn't that bad.

The nameplate on your oil boiler might be in that range, as that is about a small as they typically came when it was installed. It has no bearing on the heat loss.

Oversizing leads to really poor efficiency, and lots of wear and tear on the equipment due to short-cycling.

If you go with the smallest modcon you can find, you will still have an oversized boiler, with plenty of capacity to also heat the finished basement. The boiler will never even break a sweat. Look at the TT Solo 60 and the Knight WHN055. Maybe the HT Products MC50, too.
 
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Old 06-21-11, 12:47 PM
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This is from my contractor:
As far as the BTU rating for your home goes you can find plenty of BTU calculators on the web but what they don't take into consideration is your homes old piping and radiators the have scaling and sediment and more friction loss then when it was new. We will flush your existing pipes and radiators, this helps but its still not as efficient as new.
I would not go any less then an 80,000 BTU boiler on a middle of group dwelling with existing piping such as yours.
The rule of thumb say if your system is 25 years or older and you go with a 80% boiler you can save 15-20% of your current heating costs and a 90% plus condensing boiler you could save 60-70% of current heating costs.
I hope this helps and if you see or hear of other brands I will certalnly investigate those for you.

Your comments are welcome...

Lou
 
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Old 06-21-11, 02:01 PM
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Unless you had severe leakage in the original system the chances are the pipes and "radiators" are as clean inside as the day they were originally installed. Pipes and radiators do NOT accumulate scale and sediment from a properly maintained and operated hot-water heating system.

Your contractor is advocating a far larger boiler than necessary for the plain and simple reason that you will not complain about any lack of heat with a larger than necessary boiler AND that the newer boiler will give you a somewhat lower fuel bill. Install the correct sized boiler and you will have the best of all worlds, lower initial cost, lower maintainance costs and lower operating costs.

Oh, if I were you I'd also look for a different contractor.
 
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Old 06-21-11, 02:02 PM
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Originally Posted by Ednor View Post
This is from my contractor:
As far as the BTU rating for your home goes you can find plenty of BTU calculators on the web but what they don't take into consideration is your homes old piping and radiators the have scaling and sediment and more friction loss then when it was new. We will flush your existing pipes and radiators, this helps but its still not as efficient as new.
I would not go any less then an 80,000 BTU boiler on a middle of group dwelling with existing piping such as yours.
The rule of thumb say if your system is 25 years or older and you go with a 80% boiler you can save 15-20% of your current heating costs and a 90% plus condensing boiler you could save 60-70% of current heating costs.
I hope this helps and if you see or hear of other brands I will certalnly investigate those for you.
I think you need to talk to another contractor - this one is full of it.

I don't believe you told us the type of pipe and heat emitters. But a dab of scale wouldn't justify such gross oversizing of the boiler. Contrary to your contractor, all radiators are 100% efficient - just the rating, Btu/hr-ft could be slightly affected over time. It would be simple to estimate the total radiator rating, Btu/hr - but if it's low, which I doubt, jacking up the boiler size won't compensate for it.

As for an increased friction factor in the piping, that is very unlikely to be a problem with a system with adequate air removal device(s). And, if it were a problem, it could only be solved by replacing the piping or by intalled a larger circulator, not by installing a larger boiler.

Ednor, in an earlier post, you said this: "I did the heat loss calculation and came up with 16,785 BTU/hr loss. This appears to convert to 45,000 BTU output according to the slant fin program." I can't fathom how 16,785 Btu/hr converts to 45,000 Btu/hr. I fear that we're going around in circles here.

Also, his claimed fuel savings of 60-70% by going to a 90% efficient boiler is a pipe dream. It would be interesting to see his math. If your existing boiler is, say, 70% efficient, going to a 90% boiler will save 22% in required fuel input. (My calcs are available on request.)
 

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Old 06-21-11, 07:23 PM
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Originally Posted by Ednor View Post
This is from my contractor:
As far as the BTU rating for your home goes you can find plenty of BTU calculators on the web but what they don't take into consideration is your homes old piping and radiators the have scaling and sediment and more friction loss then when it was new. We will flush your existing pipes and radiators, this helps but its still not as efficient as new.
I would not go any less then an 80,000 BTU boiler on a middle of group dwelling with existing piping such as yours.
The rule of thumb say if your system is 25 years or older and you go with a 80% boiler you can save 15-20% of your current heating costs and a 90% plus condensing boiler you could save 60-70% of current heating costs.
I hope this helps and if you see or hear of other brands I will certalnly investigate those for you.

Your comments are welcome...

Lou
Find a new contractor. Here's some reasons why:

1) you don't have 80k worth of emitters in the house. Add up the BTU/hr output of your emitters at a normal water temperature of 180F. Betcha it's not more than 30k. You could have a 2 million BTU/hr boiler in your basement, but your emitters can't use it. Your heating system is not Nigel Tufnel's amp from Spinal Tap; it does not go to 11....

2) IF you really had a scaling and sediment problem (doubtful), then the emitters would be limited to XX,XXX BTU/hr output for a given water temperature, say 180F. Same deal as 1 above; your emitter output is the upper end of your boiler size. You don't need a boiler bigger than XX,XXX BTU/hr output. And you probably need one less than that, because most emitters are oversized, and become more so as you improve the building envelope with insulation and air sealing, new windows, storm windows/doors, etc. over time. In contrast to boiler oversizing, emitter oversizing esp with a modcon, is good. You can use a lower water temperature to meet the heat loss and realize the higher efficiency.

3) IF you had enough scale to create a friction problem (doubtful), you can upsize the pump. But the fact is that 99% of all hydronic systems are way, way overpumped and rarely achieve their design temperature drop from supply to return -- it's usually much less because of the overpumping.

4) Even if you were underpumped, water temperature dominates over flow rate in terms of determining emitter output. Cutting flow rate from say 4 gpm to 1 gpm (75%) only reduces emitter output by around 5%.

5) His rule of thumb for energy savings has no basis in reality. Every installation is different, and the savings do not cluster as he describes.

So find someone else. It would not be unusual to get 1 out of 5-6 contractors who actually know and understand how to do this right. This guy, I would not let install a modcon boiler in my house if he paid me.
 
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Old 06-22-11, 04:13 PM
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First of all, I want to thank you all for your time and input.

After speaking to a friend of mine, I have decided to add integrated domestic hot water when I upgrade the boiler and lose my 10 year old water heater. I would like to know if this will affect the sizing of the boiler and what size storage tank you would recommend. Hot water needs are based on four people bathing and one dishwasher.

I would like to measure the total surface area of my emitters, since I have some time. They are in-wall convectors and the length varies (28"-36") depending on the room. The fin arrangement is about 5"x5" over the length.

Not sure about the rules on this board, but if anyone has a suggestion for a qualified person in Baltimore, I would like to hear about him.

Thanks again,

Lou
 
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Old 06-22-11, 04:23 PM
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Lou, measure the height of the cabinets also as this has some bearing on output as well. If you can see down into the fins with the cover off (you should be able to) see if you can tell how many tubes are running from end to end. And of course the length. With this info it should be easy enough to determine the output.

I think it's OK to ask about contractors, but I would request that if anyone has any recommendations to send Lou by PRIVATE MESSAGE only... because it's NOT ok to post this on the forum.
 
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Old 06-22-11, 07:32 PM
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Originally Posted by Ednor View Post
I have decided to add integrated domestic hot water when I upgrade the boiler and lose my 10 year old water heater. I would like to know if this will affect the sizing of the boiler and what size storage tank you would recommend.
Adding an indirect for your domestic hot water (DHW) most often does not affect the boiler sizing. The high-efficiency modcons you are considering generally come with a control package that allows "indirect priority" aka "DHW priority". Basically this allows the boiler to turn off the space heating for a few minutes and direct its full output to the indirect. Depending on how much recovery is needed, that's often around 10-30 minutes. The building (especially yours with low heat loss) will not cool off perceptibly during that time.

There are several flavors of indirect, including:

) Stone-lined with coil, such as Burnham Alliance.

) Tank-in-tank, such as Triangle Tube SMART.

) Coil, such as HT Products SuperStor.

The better models of tank in tank and coil come in stainless steel (e.g., SuperStor Ultra), which is pretty durable.

Each flavor has its pros and cons, and its adherents and detractors. Any one of them, properly installed, will provide years of reliable service.

As for sizing the indirect, a ~40 gallon unit is often specified for a 'typical' family load. There are a number of sizing guides on the internet, such as http://www.comfort-calc.net/indirect_sizing.html.

The smaller modcons suggested in earlier posts would be fine for a typical DHW load when used with DHW priority. They would ramp up to 50-60k BTU to recharge the indirect. For example, a boiler with 55k BTU/hr output could take a whole 40 gal tank of 50F water up to 130F in around 30-40 minutes.

Which reminds me, another thing you can/should do is run the tank at ~140 and use an anti-scald mixing valve on the indirect outlet to temper it to a safe temperature (~<120F) at the taps. That not only kills bacteria, but is also increasingly required by local codes, and will give you a bit more effective capacity since you are mixing the hot with cold so not using hot at full blast of say 2.5 gpm showerhead.
 
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Old 06-24-11, 03:26 PM
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NJ Trooper,
The height of the cabinets is 22". Total length of convectors is 270" or 22.5'. There are three tubes in each convector. Fin width is 5", height is 2.5"

Lou
 
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Old 06-24-11, 04:31 PM
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Probably around 1200-1500 btu/ft... or thereabouts... not knowing the manufacturer of yours, so going by specs from several manufacturers. Let's take the high estimate of 1500 / ft and say that it appears that you have appx 33K BTU of installed heat emitters.

Taking the lead from the previous postings, one can deduce that if your home has been heated adequately by these convectors in the past, your total heat loss can't possibly be higher than the output of your emitters. And, one must realize that what Xiphias said about have a 2 megamillion btu boiler is so true... if you can't get the heat out of the water, what's the point of having a bigger boiler?
 
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