New Boiler Sizing Opnions Needed

Here we go again; ...I know this forum's been thru this before but:

My 114,000 BTU New Yorker water boiler just melted a hole thru itself in the rear and I need to size up a new one. My home's insulation, etc. has not changed from when it was built in 1979.

But when I put all my info into the Slant Fin's Heat Loss program, it's telling me 40,000 BTU's!! (vs. the 114,000 I have).

Can this be right? I noticed that there isn't a place in the program to account for domestic hot water which is what I will need also.

So how much more do I add since all of our hot water will be produced by the boiler as well?

I have a 1300 Sqr Ft ranch home in central Pennsylvania and I have 80 feet of finned baseboard which matches almost exactly what the Slant Fin program recommended.

Thanks for any and all comments! -Tony

P.S. I have a lower level that's got a 3rd zone with finned baseboard which I added, but it takes very little effort to keep it warm in there. Before I added the 3rd zone down there, in the dead of Winter, it was about 64 degrees just from the radiant heat of the furnace alone. SO I am thinking that not even adding that to the BTU's needed is OK.

 

Yes that figure you got can be right. That's about 25 btu per square foot.

Given that a heatloss calc already is overstated don't add on for domestic unless you have MAJOR domestic hot water requirements.

What are you using for fuel?

 

Your house sounds typical. The existing boiler is oversized by a factor of almost 3. If you intend to add an indirect water heater & put it on a priority zone, just size the boiler for the larger of the two loads (heat or domestic) which will most likely be the domestic.

 

I have oil.

Also, I don't have enough money to do the indirect tank, so I will have to size the boiler up for the coil in the boiler then add a tank later (I assume I can do that).

I called for a price on a new boiler and the guy told me that anything under 85,000 BTU's won't be able to keep up with the domestic hot water demand. That explains why they put a 114,000 BTU in originally I guess.

 

I service dozens of boilers firing .75 gph & no problem with hot water. Three quarters of a gallon of fuel oil is 105,000 btu/hr INPUT. If you figure 80% combustion efficiency, this gives you 84,000. I presume the 114,000 is output rather than input?

Even if I am not a big fan of them, you might want to look at Energy Kinetics System 2000. They are not inexpensive when compared to a lot of other steel boilers but they are efficient & do a great job of making domestic hot water with their plate heat exchanger.

If you are looking at cast iron boilers, most which have a tankless coil are "pin" boilers. In general, a pin boiler is not a good match with an indirect or any cold start application unless piped with a thermostatic by-pass. An inexpensive steel boiler with which I've had pretty good luck over the years is Thermo-Dynamics but again, they are not a good match with an indirect.

Even if you had to borrow the money to do the good boiler & indirect, I think it would be a worthwhile investment. Just food for thought. You know your financial situation better than any of us.

 

On the heat loss: 40k BTU/hr sounds about right for that kind of building in Harrisburg's climate. In any case, it's unlikely that you are off by more than 10-15%, so worst case you might be up around 48-50k BTU/hr.

There are at least a couple schools of thought about sizing for the indirect.

One is size the boiler to the larger of the two loads (in this case, the indirect load). (What Grady said.)

Another is to size for the heating load, and make sure you run the indirect on a priority zone (What Who said, also what Grady said about priority.)

A hybrid school would say size for the heating, use a somewhat larger tank than necessary so you have some reserve capacity to handle "dump loads" (e.g., big hot bathtub; or two showers at once), and use priority to run the (longer) recovery cycle.

Another hybrid school would say to size to the heating load, use a normal or larger sized tank, use priority, keep the tank at 140F and use an anti-scald mixing valve on the domestic output of the tank to keep water temps at the taps at <120F. A tankful of 140F mixed down means you are effectively drawing down the tank at a lower rate. For example, a full-hot shower with 120F water straight from the 120F tank is drawing 2.5 gpm. A full-hot shower with 140F water in the tank, mixed down to 120F draws something like 1.8 gpm. So the rate of drawdown is ~25-28% slower.

I happen to have the last option. It works quite well with a plain vanilla 40gal indirect serving 4 people.

I think you could reasonably do a 26-40 gal indirect with a boiler having a DOE output of 50-70k BTU/hr if you run it on a priority zone with it's own circulator sized for optimal flow rates.

 

The thing is: I can get a columbia oil boiler for only $1350 (delivered to my home). It's the 98,000 BTU output which does 5 GPM with the coil (vs 3 on the lower model). See www.columbiaboiler.com/residential/emerald/

It's hard to pass up a full replacement for only $1350 plus the cost of having a tech fine tuning it. I plan to plumb it in myself.

BTW, what's a normal price for someone to come in and make the final burner adjustments, etc?

Thank you once again folks! -Tony

 

"what's a normal price for someone to come in and make the final burner adjustments, etc?"

Well "normally" they don't charge a thing for that because they make their money installing the whole shebang. If you install it yourself, don't expect cheap help in getting it set up properly. You may or may not have installed it in a poper manner and they may be very reluctant to touch it for fear of the fact that if anything goes wrong they may be held liable. Be aware as well that with you installing it yourself, any warranty recourse is probably severely limited.

I'm not saying that doing a self-install isn't an option, just that it may be very tough to get support for it, both for local servicing and for factory support.

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Personally, I'd borrow a bit to cover the indirect and a nicely sized boiler. Once installed, you'll start saving and not have to worry about when to move on to phase II.

 

Does anyone know what an average/normal price is for fine-tuning the system to burn efficiently?

-Tony

 

It would depend upon the labor rates in your area. Tuning of an oil burner takes about one or two hours normally but depending on several variables it could take as long as a full day.

Why don't you simply call oil burner service companies and ask? Be sure that you ask if they use calibrated combustion testing equipment and will give you a printed report. If no testing equipment or report then go on to the next service company.

 

Furd ...thanks! That's the info I probably need.