new boiler needed - 4 options - what to choose?

neekneek

I live in New England and we need to replace our old Weil-Mclain natural gas boiler. It goes with our existing 15-year-old 40GAL indirect tank which we will continue using. We have a 1500 sq ft house with 1 bath, 2 zones, baseboard heating. We got 4 different brands to choose from.

What would be your recommendation?

Any brand you prefer? Any maintenance issues I should consider? Is higher BTU better?

What do you think we should do?

95% efficiency

HTP ELU-120WBN (120 BTU)

2. Exalt Ideal-IDEXFS155S (155 BTU)

3. Burnham ALTAC-(136 BTU )(this is COMBI - option was suggested by a plummer who told me to install it with the indirect water tank. And if the water tank ever fails, it does not have to be replaced. Not sure if that makes sense to you?)

84% efficiency

4. Weil-Mclain Direct Vent Boiler (119K BTU)

Jamie Hall

You haven't done step 1. You need to do a heat loss calculation on the house to determine your boiler size. Without that you are just guessing how big a boiler you need. Just a wild donkey guess based on your house size... all four of those are considerably bigger (too many BRUh) than what is required. In fact, even the smallest one you quote may turn out to be twice as big as needed, even assuming relatively poor insulation and druaght sealing.

So do step 1 first.

As to classes of boilers -- your number 4 will be less expensive to purchase and install, and much less expensive to maintain. Will the difference in efficiency make up for the increased invested capital and the additional maintenance? We go round and round on that one -- which suggests rather strongly that it's a tossup over the likely 10 to 15 year life of the high efficiency units.

As to which brand? You aren't buying a TV set. You are buying a heating system, and other than correct sizing correct installation by a knowledgeable person who will also be doing the maintenance is absolutely essential. Even the best boiler can be converted into a basket case by poor installation, never mind poor maintenance.

neekneek

Thanks for your thoughtful comment! Our house is old and poorly insulated. Does that mean that a higher BTU is justified? And I hear you about the importance of proper install and maintenance.

Any thoughts on the reasoning behind installing a combi boiler in connection with an indirect tank (in case the tank ever fails)? Is that common?

Finally. You mention number 4 is much less expensive to maintain. Why is that? The installers did not mention that.

Jamie Hall

On the heating load. The main property which i maintain is over 200 years old. No insulation (like... none) and rather poor draught sealing. Location is northwest Connecticut, and the design temp (usually reached) is minus 15 F. At that temperature, it has a verified heating load of 40 BTUh per livable square foot. Most more modern houses have better insulation -- or at least some -- so it's unlikely that your load would be greater, and likely much less.

Which means you are looking at a maximum BTUh requirement for your boiler of 60,000 BTUh.

And bigger is most assuredly NOT better.

Your number 4 is a plain vanilla cast iron boiler. One of the best made. It has no complicated controls, no variable firing rate. It's either on or off. It takes a few hours of maintenance every year. That's it. The others have various complex controls, and require more control on the piping and pumps -- all of which is expensive to buy and keep calibrated. Yes, the efficiency is better. No question. But... sometimes simple has its points. Also, it's built like a tank -- and will probably outlast a high efficiency boiler, two to one.

Combi boilers are only needed if you have no other source for domestic hot water -- and are only correctly sized for the loads in rather restricted conditions. Where they can be properly sized for both loads (domestic hot water and heat) they're fine. Otherwise, in my opinion at least, they are best avoided. And they are NOT needed or wanted for an indirect tank -- an indirect is heated by the main heating boiler.

EdTheHeaterMan

The average life time of a modulating condensing boiler (ModCon) is on average 15 to 17 years. This is based on experience because they became popular in the 1990s and very few of those 1990 boilers are still operational. They have been replaced with the "NEWER" version of that same design.

On the other hand, how old is your Weil McLain Boiler that you are replacing? My guess might be over 25 years old. Personally there are many cast iron (On/Off) boilers that I have installed over 30 years ago, that are still operating today. That is because they are easy to maintain and built like a tank!

I know of at least 3 ModCon boilers that I installed in 1995 to 2005 that are no longer in service. And I know that because I did the Second ModCon install myself before I retired in 2020. I think it is experience like this that has many of the professionals on this site touting the virtues of the lower cost lower efficiency boilers on smaller buildings. When a new technology has the ability to lower energy costs by as much as 30% over the boilers of 40 years ago, then you need a large usage to justify the large price since the equipment only has half the expected life span of older technology.

If you have a $6000.00 annual fuel usage and you can cut that by 30% then you will have a $18,000.00 savings in energy over ten years but that appliance will cost you $5000.00 more compared to the lower cost boiler. So you might agree that the extra cost is reasonable.

If however you have only a $1000.00 per year total cost then the savings will only amount to $3000.00 over the next ten years then the extra $5000.00 is maybe not the best idea. It is an economy of scale. You need to do the numbers based on your situation, not based on what the salesman says someone else may have saved based on their fuel usage that is much greater than yours. Only you can know if the extra expense is worth it

neekneek

Wow. thanks so much for this repsonse!

The way you describe number 4... sounds appealing and simple indeed. Straightforward and easy to operate, trust, maintain. But I mostly got salespeople offering me high efficiency units...

One thing I forgot to mention is that our local energy provider has zero% interest loans only for 95%+ boilers (not cast iron Weil-Mclain, 84%). Maybe the sales people I spoke to steered me in the direction of a high efficiency boiler, not purely because of its performance, BUT... because the easy/cheap financing option is appealing to customers!

Food for thought for sure.

EdTheHeaterMan

neekneek said:

Wow. thanks so much for this repsonse!

The way you describe number 4... sounds appealing and simple indeed. Straightforward and easy to operate, trust, maintain. But I mostly got salespeople offering me high efficiency units...

One thing I forgot to mention is that our local energy provider has zero% interest loans only for 95%+ boilers (not cast iron Weil-Mclain, 84%). Maybe the sales people I spoke to steered me in the direction of a high efficiency boiler, not purely because of its performance, BUT... because the easy/cheap financing option is appealing to customers!

Food for thought for sure.

That is certainly a factor to consider. That zero interest isn't coming from an over priced contract on the boiler you are purchasing. In most cases there is a fund that is maintained by the utility companies that you have already paid into on your gas and electric bill. So since you paid for that fund in your monthly payments to the utility, and the only way you can access that money is to get the 95% efficient boiler, then you need to consider ALL the cost of ownership. If you get the higher price boiler and you don't need to put all of your own money into the purchase, then that is certainly a savings to be considered.

Sometimes that 0% money is the balance point that will make the higher priced job the lower cost job in the long term. Since we are not supposed to Quote actual job prices on this forum, I can only give you hypothetical savings numbers, however I used to have an Excel Spreadsheet. This would factor in actual fuel prices, along with service and maintenance costs over a 25 year period along with inflation of the energy costs, and give you a year by year print out. When I would plug in the numbers using YOUR actual energy bill using the existing boiler over the last few years, and compare it to the cost of the job plus the lower fuel bills over 25 years, I would always recommend the job that paid for itself in 10 years.

Sometimes that would be the lowest cost boiler, sometimes that would be the higher cost boiler. It all depended on the conditions of each individual customer.

HVACNUT

What model Weil McLain? If I had to choose from the choices given it would be the WM just based on BTU's. The indirect might not get full rated input, but with one bath it won't be an issue. Have the installer make sure the piping and circulator is correct for the water heater. If not, now's the time to fix it.
One question I would ask is, "If there's a problem down the road, which boiler will a tech most likely have repair parts for in the van. Or in stock at the local distributor and they can get it right now. Or it needs to be shipped from who knows where and will take 5 business days... and it's Christmas. 

neekneek

Thanks. this is the model Weil McLain that was proposed:

https://www.afsupply.com/weil-mclain-381359006-cgi-5-88-000-btu-output-natural-gas-boiler-with-t007e-circulator.html

Hot_water_fan

A right sized boiler is best. The 95% efficient (modulating condensing or modcons) boilers can vary their output. The lowest they can go is 8,000btu. That’s usually paired with an output of 80kbtu. That’s probably 2x your heat loss, so that’s a fine option. All of those manufacturers make an 80kbtu size. 

A lower efficiency model needs better sizing. You can use your fuel use to calculate the size: 

https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler

The CI boilers come in limited sizes and you’ll probably find a 50kbtu boiler comes closest. 

LRCCBJ

neekneek said:

Thanks. this is the model Weil McLain that was proposed:

https://www.afsupply.com/weil-mclain-381359006-cgi-5-88-000-btu-output-natural-gas-boiler-with-t007e-circulator.html

If you decide on the CI boiler, this is the size you need:

https://www.afsupply.com/weil-mclain-381359004-cgi-4-66-000-btu-output-natural-gas-boiler-with-t007e-circulator.html

DO NOT let the contractor use the cgi-5, no matter how much he screams that it will not work. Others will confirm and might even suggest the smaller cgi-3 but this would depend on your hot water usage more than the CH load.

ethicalpaul

Your number 4 is a plain vanilla cast iron boiler. One of the best made. It has no complicated controls, no variable firing rate. It's either on or off. It takes a few hours of maintenance every year. That's it.

Does a natural gas boiler even need maintenance every year?? Other than that question, I agree with everything @Jamie Hall told you.

I like fancy tech stuff a lot, but I'll never buy any boiler other than a basic gas model like your #4

gyrfalcon

Is your current boiler natural atmospheric draft? Or is it induced with a blower motor? The reason I’m asking is the cast-iron Wei McLean Being offered is the CGI model which is induced draft meaning it has a blower attached to it if you need Atmospheric draft the CGA is that version. 

pecmsg

120
155
136
119
BTU/h

No one has done a load calculation yet!

for 1500 Sq Ft there all oversized.

neekneek

The companies that visited did not mention anything about a load calculation. I think they just based their suggestions on the old WM boiler that was 105BTU.

ethicalpaul

That's what the bad/lazy contractors all do. Find another one that will find out what you actually need

pecmsg

neekneek said:

The companies that visited did not mention anything about a load calculation. I think they just based their suggestions on the old WM boiler that was 105BTU.

and who said it was right back then? Have any improvements been made to the envelope, Doors, Windows, added insulation caulking?

The only way to know is to have a load loss calculation performed. AKA Manual "J".

hot_rod

Even if the load  is on the very high side, say 30 btu/ sq ft, you only need  45,000
An 80k mod com would cover the load nicely, possibly run 90% plus in part of the season, provide near constant circulation with outdoor reset.
check for incentives in your area for high efficiency upgrades

www.dsireusa.org

MaxMercy

Two points - get that heat calc done as Jamie suggested. When my builder-installed boiler needed to be replaced after 30 years, I simply bought one the same size and installed it myself - this was before I joined this forum. Well, the new boiler (even though it's an "on/off" cast iron affair) is more efficient than the original, and it short cycles like crazy. I contacted Slant Fin and they said the lowest I could downfire the boiler was to 0.85 gallons per hour, so I installed a .85 @100 lbs and set the combustion to match. It still short cycles except on the coldest nights when both zones call. In other words, my boiler is too big. I'm probably outputting 117Kbtu/hr on a 2800 sq foot house.. I wish I had bought a smaller boiler. Note that my house is pretty well insulated though. Fortunately, in Connecticut, I'm burning about 700 gallons for the whole year including hot water through the summer so I'm not getting killed at least.

Tighten your envelope! Regardless of what you're using for heat, there's no reason not to at bare minimum fully insulate your attic, get storms installed on your windows if they are single pane, make sure your doors don't leak, and insulate any ductwork. A tight house not only uses a lot less energy to heat, it's far more comfortable at the same thermostat setting.

HVACNUT

Hypothetically, if the indirect specs 140K BTU input @ 180° to meet its ratings (with correct piping and circulator), then you might wind up sizing the boiler for the indirect. With most mod cons, you can lower the max firing rate and work off ODR and modulation for the space heat.

GGross

Those indirect ratings are there to help you size the system, they are not a firm requirement to produce hot water, but rather just there to show you how the system will perform under certain circumstances. Generally a good indirect will also offer pressure drop charts so you can size the boiler you need properly, you only need to go with the rated input rates if you require that much hot water, which a single bath almost definitely does not need 140kbtu on an indirect. Basically a standard 40 gallon water heater would be enough here, so for an indirect you only need to figure for about 40k BTU

ethicalpaul

140K for an indirect? Gosh I wonder why so many systems are oversized! What is that, the requirement to raise the temp from 33F to 140F in 1/2 hour???

gyrfalcon

Being that the OP is in New England, where boilers are more common, hopefully they can get a bonafide contractor to do a heat load and provide good service on the installation.  

Jamie Hall

ethicalpaul said:

140K for an indirect? Gosh I wonder why so many systems are oversized! What is that, the requirement to raise the temp from 33F to 140F in 1/2 hour???

Good heavens. Sanity check time here, folks. An indirect does NOT require 140K BTUh. It may be able to transfer that much power, quite true. But just because it can transfer that much power to the domestic hot water doesn't mean it needs that much power to operate. It should operate very nicely, thank you, on somewhere around 15,000 BTUh. Like any other storage water heater -- indirect, gas, oil, electric, even heat pump-- there are two factors. First, how much water does it store? Second, how fast does it recover? It's a bit of a balancing act, but if you have fast recovery (oil, gas) you don't need that big a tank. If your recovery is slow (electric, heat pump) you need a bigger tank, depending on usage. An indirect can be, effectively, either one, depending on how much power you want to draw from the boiler.

EBEBRATT-Ed

Many are happy with the operation of a 40-50 gallon gas HWH in a typical home with 1-2 bathrooms. They usually are around 40,000 btu input. I am using that just for reference.

So a similar 40-50 gallon indirect set up for 40,00 input will do the job in most cases. I still pipe the indirect with 1"

ethicalpaul

HVACNut did say "hypothetically" so maybe my response wasn't appropriate

HVACNUT

Sorry people. Maybe my hypothetical tank and BTU's math didn't correlate to most of you living in real life, but in the areas I serve there are a plethora of houses that need more domestic load BTU's than does space heating. 10K sq ft, (2) 119 gallon indirects, with a 180K BTU boiler isn't going to cut it when there's a full house or party going on. Multiple kitchens. Multiple laundry machines. More baths than I have blades of grass on my lawn.  Ridiculous? Maybe. But not atypical. Where I am anyway.

Hot_water_fan

@HVACNUT pretty cool that Tony Soprano is a client of yours! 

hot_rod

You always size to the larger load, in some cases that will be the DHW
This  is why we ask questions and some up upfront calculations. There is no one size fits all.

HVACNUT

Hot_water_fan said:

@HVACNUT pretty cool that Tony Soprano is a client of yours! 

It's pretty gross, actually. 

teddell

DO NOT BUY an HTP boiler!!! I had one installed in October of '21. Within the first year, it was having problems (internal leaks, error codes, etc.). At two years, it failed completely and had to be replaced. It was a battle to get the manufacturer to do anything about it, even when we were without heat for six weeks in the middle of winter. Months later, I'm still fighting to get the out of pocket expense covered by the manufacturer. Long story short, buy a different brand, HTP is junk.

pecmsg

teddell said:

DO NOT BUY an HTP boiler!!! I had one installed in October of '21. Within the first year, it was having problems (internal leaks, error codes, etc.). At two years, it failed completely and had to be replaced. It was a battle to get the manufacturer to do anything about it, even when we were without heat for six weeks in the middle of winter. Months later, I'm still fighting to get the out of pocket expense covered by the manufacturer. Long story short, buy a different brand, HTP is junk.

How much was HTP’s problem and how much the installation?

only the contractor can deal with the manufacture. 

teddell

It was all HTP. I was able to deal directly because I called them.

LRCCBJ

Jamie Hall said:

Good heavens. Sanity check time here, folks. An indirect does NOT require 140K BTUh. It may be able to transfer that much power, quite true. But just because it can transfer that much power to the domestic hot water doesn't mean it needs that much power to operate. It should operate very nicely, thank you, on somewhere around 15,000 BTUh.

Just so others on the forum understand the implications of this statement:

15K BTUH will deliver .41 GALLONS PER MINUTE. Truly insufficient to recover an indirect in less than two hours. Sure, if you want to take a shower with a 30g indirect, go ahead...........you have about ten minutes at 3 GPM unless you store considerably higher than 130F. The boiler would, effectively, provide nothing.

Such a choice would demand an 80g indirect as a minimum..........and a lot of patience.