Please help me determine size of a replacement boiler

I read on this woderful site an almost 2 1/2 years old thread dedicated to this subject. It was very helpful and it looks to me like I have been a huge sucker for 27 years.

Now, I must replace within a couple of months the boiler in my 2,400 square feet 34 year old house, with 2.5 bathrooms, replaced windows, good insulation, etc. I have 4 bedrooms and we are 2 people still living here. Most likely we will have to sell within 3-5 years and move into something smaller.

The unit to be replaced is a 10 years old New Yorker AP-790 with a heating capacity of 149 MBH. It has been satisfactory: excellent on heating (2 zones) but could use a bit more hot water as I like to soak in the tub... but not vital.... Never had any major problems with two showers going at the same time even with two kids in the house and frequently a house-full of guests.

Got three offers:

1. A Burnham V84 at 159 MBH for $5,500 installed. A new expansion tank is included (capacity not mentioned) but I am not sure if this is the same as the tank Moose was talking about in the old thread I read). Lots of sundries included as well which I assume should be standard for any installation.

2. A Weil-McLain WTGO-4 at 145 MBH for $5,200 installed, Extrol tank (whatever that is - probably similar to the expansion tank) and again a slew of sundries.

3. A Buderus GB125 BE/30 at 102 MBH (only 100 MBH in catalog for 178/140 degrees Fahrenheit) for approx $ 11,400 plus two programmable thermostats Honeywell FocusPro 5000 at $350 each. Offer not finalized and an alternative for a GB 125 BE/22 at 75 MBH for approx. $9,600 is also under consideration. Wonder if I will ever amortize the price difference by higher efficiency and lower size on the Buderus... but that's for me to decide. This contractor came with a heat loss calculation showing 43,083 BTU. He used the data available publicly on my house. Even had a picture of the house (!!??).

My question: Going by NJTrooper's comment on 10-14-08 09:37 in the thread I read, at 30 MBH/sqft, all I would need is a 72 MBH unit... or less... as he says. Have I been running too big a unit for all these 27 years I spent in this house, throwing money down the drain for too much oil? Or is the Buderus guy trying to sell me be a bill of goods?

A word from anyone who knows (a lot) better than I do what this is all about, would be very much appreciated.

 

How are you generating your hot water now and will that change with a new boiler?

 

Keep one thing in mind... just because your boiler has twice the capacity you need, does NOT mean that you've burned twice the oil that you should have! Will a properly sized boiler burn less, yes, but don't expect half the fuel bill!

A well constructed home with good insulation and infiltration sealing will usually fall in the ballpark of say 20-30 BTU / sq ft ... based on that, your heat loss will fall somewhere between 50 and 75 MBH... but that is only a 'rule of thumb' and should not be used to size a new boiler. (although, with oil fired units, you won't find many below say 70MBH)

If a contractor can't/won't/doesn't know how to do a proper heat loss calc, keep shopping. The first two guys can't be bothered... they just want to install the same size or larger yet boiler, take the money and get out.

Take a long look at the Burnham MPO boiler.

U.S. Boiler:: MPO Boiler, Unique 3-Pass Cast Iron Design

Are you planning on spending the next 27 in the same home? Give very serious consideration to NOT using a 'thankless' coil in the boiler for domestic hot water. Think INDIRECT WATER HEATER.

By the way, the Buderus quote... does that include an indirect water heater?

 

Why does the boiler need to be replaced in the next few months? At 10 years old, it has a lot more life in it, assuming it's reasonably properly installed and maintained.

There are lots of things to do that can improve the overall system performance before you get to ripping out a perfectly decent boiler.

 

Drooplug: Hot water is generated in the same boiler as the one used for heating.

 

Xiphias: The heating company maintenance guy said that since I had a steel boiler it may crap out on me in the middle of next winter. He showed my wife a few cracks but by the time I came down the boiler was closed back up. It can be that the guy who installed the New Yorker 10 years ago did not use the best possible equipment available on the market.... Yes, 10 years seemed kind of a short life to me too. The previous boiler lasted 15 years. No idea how to make sure they are not trying to take advantage of us other than by calling yet another contractor... But they al want to make a sale, rather than help the consumer...

 

Trooper: thank you for the thorough response.

Understand that a double capacity does not necessarily mean double consumption. Any rule of thumb for a realistic ratio?

If the heat loss is 50-75 MBH (the Buderus man calculated 40 MBH), it looks like a 75 MBH heater would be sort of border line: is this correct? Should I go for a bigger one? How much bigger?

The first two guys struck me exactly as you say. That's why I called in the Buderus guy. But his proposal seems to be way high, particularly since we are not planning to spend another 27 years in this house: a 4 bedroom for two people when the kids are gone seems to be overkill... much as we loath to move as we are attached to the house and the neighborhood. Most likely we will have to sell within 3-5 years... as I see it now.

Thank you for the MPO Burnham suggestion. Will look into it.

I am not too sure what an INDIRECT WATER HEATER exactly is. Any link that explains this clearly? Don't any of the three boilers that I have been quoted include such a heater? Wonder why didn't the contractors talk about it: just to make their lives easier? Could well be. Does the MPO Burnham you suggeted include such an indirect water heater? Is the indirect water heater a separate unit from the boiler? Does one have to order it separately?

 

I'd be inclined to state that the guy showed your wife cracks in the refractory rather than cracks in the steel. Steel boilers will actually take more abuse than will cast iron as long as they do not have the water changed, either purposely or via leaks. I personally wouldn't have a cast iron boiler if it was free. Even using crappy water a steel boiler can last fifty years or more.

 

You would save fuel by abandoning the tankless coil, switching the boiler to cold start, and using an indirect water heater for your hot water. An indirect is a separate water tank that uses the boiler to heat the water. It is connected to the boiler on another zone as if it were a regular heating zone. The recovery times on these tanks are very good and you will be much happier with one when you draw your bath.

 

I have had a castiron boiler now for over 20yrs. oil fire and it still comes in at 83 3/4 % when new it was 84 1/2 %.. Yes I also have a super stor water heater, which is an indirect. The only problem I have had is with the burner, which I am sure we all have at times... Mine is an utltimate, and this is the 2nd home with one.. I wouldn't go any other way. But that's just me....I would call another person and ask them see what they say..

 

Furd: Thank you for your comments. Am I to interpret them as cracks in the refractory not being a problem? If so, the guy was trying to pull a fast one... and so did the other two contractors I called in... I am tempted to complain about them at the BBB. Would you encourage me to do so? Any idea as to how I could get an HONEST opinion before chewing out these guys?

 

drooplug: many thanks for the explanation. It makes sense. Question is whether the cost of the indirect water heater can be justified by the fuel savings. I take it that an "expansion tank" as quoted by contractor 1 or an "Extrol tank" as quoted by contractor 2 is not the same as the indirect water heater you (and others on this blog) are talking about: please excuse my confusion - I used to be a mechanical engineer, albeit not in HVAC, so I understand the concepts; but since I have been doing something else for the last 25 years, the specific terminology is rather foreign to me.

 

The expansion tank is to allow the water in your heating system a place to go when it gets hot and expands. An indirect water heater is very similar to a conventional still water heater. They are both tanks of water that get heated. A conventional style has the fire inside of it for direct heating, the indirect has a coil inside that carries hot water from the boiler and through the tank; indirectly heated. The water from the boiler and the domestic hot water do not mix. They are kept separate. Indirect hot water heaters are the most efficient way to heat hot water. The way you are set up now, the boiler remains hot all day, every day including the summer.

 

You are referring to the combustion efficiency, not the total system efficiency. Almost any boiler built in the last fifty years can attain a one-shot test combustion efficiency of 80+%.

 

1077, there are two general types of expansion tanks; the "conventional" which is a steel tank usually hung from the ceiling/floor joists above the boiler and the "diaphragm" type which is piped directly to the system. The diaphragm tank will always be smaller than the conventional type and its placement is generally not as critical although there ARE rules for best operation. Extrol is the name one manufacturer uses for their diaphragm tank. Some people (installers as well as owners) prefer one type over the other but the truth is that more new installations will use the diaphragm tank than the conventional. There are pros and cons for each type.


As for the cracks...if they are just in the refractory and are not too large they can probably be ignored. Cracked refractory is all too common, especially in oil-fired boilers that "short cycle", that is, come on and burn for only a few minutes and then shut off only to fire again in another few minutes. It is the rapid heating/cooling cycle that causes the cracks. If the cracks are are long, wide or deep then they really should be filled with a suitable cement. If you have an "old time" real hardware store nearby they will likely have furnace cement that can be used to repair the cracks. If not, then a fireplace shop will often have the cement. You can often get it in a tube to fit a standard caulking gun to make it easier to completely fill the crack and also less messy. You need to first clean all loose materials and dirt/soot from the crack and then use a fine mister or a small paintbrush to slightly dampen the crack before adding the cement.

As for the BBB, my personal experience is that it isn't worth your time.

 

Furd: Many thanks - you do make a lot of sense and I am very grateful for the enlightening. There is nothing hanging above my New Yorker now so I assume it has a diafragm expansion tank. As for the cracks, I'll open the boiler and take a look. What if the cracks are not too large and I do nothing?

 

Drooplug: So in the New Yorker I have now (and presumably in the Burnham V84 and the Buderus that I got quoted) I probably have a coil inside the boiler circulating the hot water for the house (taps, showers, bathtub) separate from another coil that is used for the heating system. An "indirect", as I understand, is in effect a heat exchanger, separate from the boiler and I would have to physically see it outside the boiler unit. Did I get it right? Does ALL the hot water from the heating circuit go through the "indirect" all the time, thus heating the water all the time or is there a separate circuit that feeds the "indirect"? If the water goes through the "indirect" all the time, how does the system keep the heaters cold during the summer when the thermostats are turned down but I still get domestic hot water?

 

You are right about the indirect being separate.

The heating water does not circulate through the indirect all the time. The indirect would have it's own heating zone much like you house has 2 separate heatings zones. The indirect would be a third. There is an aquastat on the indirect that keeps an eye on the water temperature in the tank. When it drops below the set temperature, it tells the zone valve to open and the boiler to fire.

 

Unfortunately the state of heating professionals seems to be about (or worse) than you experienced. Going 1 for 3 in terms of thoughtful inspection, heat loss calculation, and proposal development is not bad. More often it might be 1 for 5....

If furd is correct about the refractory, it would save you thousands to repair it and get another 5-10 years out of it, at least. Converting to cold start and adding an indirect and some controls to enhance performance may end up costing almost as much as doing a full replacement, though.

If you plan to sell soon (3-5 yr), you will not get your investment back out of almost any decently-installed system. And heating system efficiencies are not really valued at resale (although they should be..., topic for another day and place), i.e., you won't get another 5-8 grand on your asking price just because you have a 5 yr old cat's meow boiler.

Anyway, The GB125BE is the highest of the high-end Buderus and uses a technology in the burner/fuel that is a very new approach to oil-fired boilers. There is also the more traditional vanilla Buderus, the G115WS. You might ask your Buderus guy if he would quote that. See where you end up. Buderus does make fine equipment. Really any of the boilers proposed, when properly installed are pretty good.

The G115WS/3 would be the appropriate size, and if you add an indirect water heater (which is among the most efficient ways to heat your domestic hot water) by Buderus, HTProducts or similar good brand, you would have a solid, long-lasting system.

The Buderus guy might try to upsell you a little for the "Logamatic R2107" control with the G115WS. IMHO, it is worth the money. (It also comes standard on the GB125BE.) It is a complete control package that will optimize the boiler performance for both heating and domestic hot water.

 

Xiphias, drooplug, furd: Many thanks to all of you. I will have to decide what to do and your inputs helped me tremendously.