Choosing a Boiler

Tony B._2

> As for the coils, get the <BR>
> biggest ones that fit, then you can run them at <BR>
> lower temperatures and still heat the <BR>
> house.<BR>
> <BR>
> Also note that mod/con boiler output is <BR>
> usually measured within the condensing range. You <BR>
> will have de-rate them about 10% if you're <BR>
> planning on using them at 180°F. <BR>
<BR>

Thanks for the info. I do know that the coils are described as 80,000 BTU coils, and there are three of them. Does that mean they have a capacity to produce 240,000BTUS if the boiler feeds them enough hot water?

I will check about heat loss calculation and see if one was done.

Just so I understand this correctly, if the heat loss was 200,000 and the coils can produce at or near that number...it would mean I need to use 180degree water almost all the time, and the benefits of a modulating boiler would be reduced or eliminated. If, however, the coils are rated at 200,000 but heat loss is only 100,000...then I can use a lower water temp and modulating/condensing boiler would be helpful. Is this reasonably accurate?

Thanks again for your time and patience with this novice! I am learning a lot.

Tony B._2

Choosing a Boiler

Hello, I have been reading this site for quite a while, knowing I had some choices to make, but now feel the need to ask a question of my own. We are in the process of redoing an older house. The work includes updating insulation and windows, which should help, as it was a very cold house...having NO insulation at all. We have also added on to the house so it is now approximately 3500 square feet. The heat will run on natural gas.

So far the ductwork and mechanicals for what I am told is called a hydronic forced air system has been installed. Not sure if that was the best way to go, but for various reasons, that is what we now have. Now, we are trying to choose a boiler. The plumber is a great guy who is quite capable, and has offered us a few choices. He says there are many others, but has thrown a few out to start.

Among the units mentions, at varying degrees of cost, are a Plymouth Water Series 2 (PVWB-7D), Plymouth Ultra (WPVSB-7D), and a Munchkin 199M. I included the model numbers to give you an idea of what size units we are pondering.

I know the Munchkin is more efficient than other two options, but having spoken to a few people (perhaps TOO many!) some say that the type of heat system (hydronic forced air) will not really take advantage of that efficiency, and a more conventional boiler may be better matched to such a system. In other words, they feel the 92% advertised for Munchkin will not be realized in our system, while the numbers for the conventional boilers 80-84% will be pretty accurate. If this is so, I am unsure the extra cost and complexity of a Munchkin will be worth while. What one person told us is that the type of heat system which the boiler will supply needs very hot water or the air will feel cool...and when calling for real hot water all the time the efficiency of the condensing boiler is not all that great.

Please remember...I know nothing...just repeating what various folks have told me!

Another concern is reliability. I don't mind spending extra for the greater efficiency, but have concerns about the amount of service the more modern units may require. Along with that is a concern over who can work on these more modern units. Is service as readily available as with a traditional boiler?

We will be pairing this unit (which ever one we choose) with a superstor indirect hot water heater.

I guess what it boils down to is that I'd hate to shy away from the newer technology if it will really provide some realistic gains in efficiency and, at the same time, will be reasonably reliable. On the other hand, I don't want to spend the extra dollars chasing efficiency I will never get. I am not talking solely about recovering my investment, as that is not my only goal...I'd like something more efficient simply because I'd rather use less. I drive a fuel efficient car for the same reason.

I would really appreciate any thoughts any of you experts may have. It is hard for a novice to make an informed decision, because there are such varying opinions on this. I sometimes think those who shy away from the newer technologies do so because it is out of their comfort zone...but I am not sure.

Anyway...thanks in advance for any help. Tony

Joe Brix

Strange selection

The Plymouth is a Dunkirk cast iron natural draft boiler that would require a chimney or power venting which I would highly not advise to do. The Munchkin must be PVC vented and will use outside air for combustion. I would not get a Munchkin unless you're getting the Vision boiler controls for it. You have to be trained by HT Products to sell the controls. You still may be able to use lower water temps durring warmer parts of the heating season to reap the benefits of the Munckin. But if your air handler has been designed to need 180° boiler to heat the house, then a standard boiler might be all you need. I would look into other modulating /condensing boiler options.

Mike T., Swampeast MO

If you choose a modulating-condensing boiler to drive your hydro-air system make 100% certain that the installer is VERY familiar with such systems!! I would sincerely ask for and verify references for similar systems.

Without exceptionally careful design of the ENTIRE system you'll receive little benefit from either condensation or modulation.

Old house? What type of heat before? Is existing ductwork being re-used? Did you (shudder to think) remove cast iron radiators?

Constantin

... or how about perform a heat loss calculation?

A 200MBTU boiler for a reasonably-built 3500 sq ft house seems somewhat excessive unless you live in Alaska. I wouldn't be surprised if the 140 or even the 80 could do the job if the house has been weatherized.

Tony B._2

Thanks for the replies so far...your words of caution are good advice. As to your other questions...the house is about 100 years old, but the heat had all been redone in the 60's or 70's and had a really sloppy gas fired hot water/baseboard system installed that made some rooms unbearable and left others without any heat at all. The kitchen had no radiators/baseboards at all combined with a total lack of insulation made for a chilly house! The duct work is all new. Sadly, if there were ever radiators, they were gone before we got there. We opened all the walls and the house is now totally insulated, and was wrapped with a barrier before the siding went on.

Tony B._2

I am not sure what you mean by strange selection...do you mean the choices are not good ones...or just that they are rather opposite ends of the spectrum?

The house has a chimney that was used by the old gas boiler.

I am not sure how I would know what water temperature the system was designed for I do know it is a three zone system with three separate air handlers (Lennox CBX32MV-36 3-ton variable speed air handler) and three hot water coils...(Lennox SHW2208 80,000 BTU hot water coil).

Not sure if that might allow you to determine what temp would be appropriate, or if I'd need to contact the guy who installed the air end of the system.

Thanks for the reply! It is certainly good to be able to reach real experts.

Tony B._2

> A 200MBTU boiler for a reasonably-built 3500 sq

> ft house seems somewhat excessive unless you live

> in Alaska. I wouldn't be surprised if the 140 or

> even the 80 could do the job if the house has

> been weatherized.




Perhaps I am being naive...but wouldn't they have done this automatically? It would seem like this would be a standard practice...but from your comment I am guessing it may not be!

Joe Brix

You gotta get some info from the builder

Yes, the boilers are at different ends of the efficency spectrum.

A heatloss calc should have been done. Then you're gonna need the specs of what the AH were designed to put out.
If they just gave you enough BTU output to match the heat loss, then the design expects 180 degree boiler water, a Munchkin might not be worth the extra money.

If your AH's have a great deal of excess capacity, you can probably run cooler boiler water temps. A Munchkin could save you money. Maybe your home will be very comfortable with only 140 degree water. This is especially true if you live on the coast where the worst winter temps might only last for a few days each season. With the right controls, the boiler can ramp up when the indirect needs heat for fast recovery then modulate down again for the heating zones.

Get those design numbers. Without them you don't even know what size boiler you need let alone what type. Then see what your heating contractor says. Both boilers will work. It's just your call on if the added expense will payback in a reasonable time frame.

Boilerpro_3

For a comparable heat load

My 2800 sq ft 100 year old frame home with 700 sq ft of glass here in northern Illinois calculates out at only 52,000 btu/hr boiler output on the design day, actual load appears somewhat lower. It is well insulated, weatherstripped windows and doors(originals). I would also be worried about the size of the air conditioning....I cool with about 1 1/2 tons, while the heat gain calculations show I need about 2 1/2 tons. I am about the only contractor in my six county area that does load calculations, so I certainly would not assume the calculations have been done. It is not uncommon for me to find hot water and steam boilers 3 to 4 times the size they should be both in homes and supposedly engineered commercial systems. I generally assume at least 60% oversizing on most existing installs. I had a civil war era, 2,200 sq ft home only a few blocks away with a 650,000 btu/hr steam boiler which I replaced with a similiar efficiency 200,00 btu/hr steam boiler....bills dropped about in half.

Boilerpro

Tony B._2

> Yes, the boilers are at different ends of the

> efficency spectrum.

>

> A heatloss calc should

> have been done. Then you're gonna need the specs

> of what the AH were designed to put out. If

> they just gave you enough BTU output to match the

> heat loss, then the design expects 180 degree

> boiler water, a Munchkin might not be worth the

> extra money.

>

> If your AH's have a great deal

> of excess capacity, you can probably run cooler

> boiler water temps. A Munchkin could save you

> money. Maybe your home will be very comfortable

> with only 140 degree water. This is especially

> true if you live on the coast where the worst

> winter temps might only last for a few days each

> season. With the right controls, the boiler can

> ramp up when the indirect needs heat for fast

> recovery then modulate down again for the heating

> zones.

>

> Get those design numbers. Without them

> you don't even know what size boiler you need let

> alone what type. Then see what your heating

> contractor says. Both boilers will work. It's

> just your call on if the added expense will

> payback in a reasonable time frame.

Tony B._2

> I am about the only contractor in my six county area > that does load calculations, so I certainly would

> not assume the calculations have been done. It

> is not uncommon for me to find hot water and

> steam boilers 3 to 4 times the size they should

> be both in homes and supposedly engineered

> commercial systems.


I certainly have some questions to ask. I hope I find I found someone who operates like you and they did the proper calculations before selling me more than I need.

Constantin

If you have prior fuel bills and a weather station nearby,

...we can even use those to start to get a ballpark estimate for the heat loss.

Bottom line is, a heat loss calculation is a must, even with modulating boilers. Some contractors simply don't want to go through the trouble, I would keep looking until you find one that does. Chances are that he/she will also care more about the actual install.

As for the coils, get the biggest ones that fit, then you can run them at lower temperatures and still heat the house.

Also note that mod/con boiler output is usually measured within the condensing range. You will have de-rate them about 10% if you're planning on using them at 180°F.

Joe Brix

Yes, but remember

you should only need to support that heatloss on the coldest days of the year. So most of the winter you should still not need 180° water. All assumes the system was calced out correctly. AH's usually have an aquastat so the blower doesn't come on unless the water temp is at least 140°. Maybe 140° is all you need on a 50° day. Even if you decide on a non-condensing boiler, look into outdoor reset controls to have the boiler only fire to lower water temps depending on an outdoor temp sensor. These only add several hundred dollars to the cost of the boiler.