Keystoker boiler size advice

I'm updating my heating system with a Keystoker boiler, but I'm not really sure what size. I've gotten different recommendations from three different Keystoker dealers. One says I need a KA-6, another says KFL-6, and the most recent, and the one that seems the most experienced, says a KAA-4. I'll post some info about my house in the hopes that the wealth of knowledge and wisdom on this site can give me some recommendations, thanks.

Single story ranch style house built in 1991 - Western Pennsylvania, Cambria County, 15 miles north of Johnstown
Very well insulated, r-14 insulation in the walls with 2 inch foam sheeting behind vinyl siding, brick case front and two layers of insulation in the attic - blown insulation with r-19 layered overtop
standard double hung windows
standard wall height
Pex in floor radiant heating throughout main living area - 1,640 sq ft.
Basement with 58 feet of copper radiators - heated much less than the main floor
Domestic hot water coil also needed

We heat a slightly smaller brick cape cod with zero insulation in the walls with a kaa-4. It does run quite a bit when it's below zero with high winds, but kept our house at 71/72 all winter plus provided DHW for two adults. Very happy with its performance.

Did they do heat loss calculations for your house. it appears you have about 75,000 BTU's of heating capacity now. With so much insulation, I doubt your current system is stressed.

Current system is an old fashioned Red Flash Boiler, hand fired with soft coal. It works very well, definitely not stressed, but I'm tired of the mess and the inconsistencies found in soft coal. Can't wait for the switch, thanks.

We also switched from a hand fed boiler... You will love a stoker boiler! For what it's worth, we have cast iron radiators with 77,000 BTUs of radiation.

So, is that a no on the heat loss calculation? It would give you the answers needed to select a boiler...

No, have not had a heat loss done

Welcome to the forum.

rdaubert wrote: ↑

Wed. Apr. 10, 2019 2:59 pm

Current system is an old fashioned Red Flash Boiler

NICE!

rdaubert wrote: ↑

Wed. Apr. 10, 2019 5:58 pm

No, have not had a heat loss done

There are heat loss calculators in the internet that will give you a good idea of what you need. I used this one.
https://www.usboiler.net/heat-loss-calculator.html
You make a few measurements, count windows/doors and factor in your insulation. Once you have a number, add 10% to 20% for a pickup factor. Add 10,000 to 30,000 BTU's for DHW and you should have a good heat loss number.

-Don

Your coal burner needs to be about 80% of the conventional appliance heating it now.

I completed a heat loss calculation and determined that the KA-6 is really unnecessary for my house. That leaves the KFL-6 or the KAA-4. I called Keystoker and they told me that the KFL-6 has the same size boiler as the KA-6, but the same burner as the KAA-4. Also, said that they are most likely discontinuing the KFL-6. I'd rather avoid purchasing a unit that is gonna be discontinued. That leaves the KAA-4 or the KA-6. Heat loss calculation shows that a KAA-4 would work. Considering everything I've posted, can anyone give me a reason to spend 1000 dollars more on the KA-6?

Discontinued means little...only discontinuing the configuration, not the components used in the configuration.

rdaubert wrote: ↑

Fri. Apr. 12, 2019 9:23 am

Considering everything I've posted, can anyone give me a reason to spend 1000 dollars more on the KA-6?

Not only a waste of money but a waste of coal. Depending on where you live the large majority of your boilers time will be just keeping itself lit and idling. the larger the fire bed the more coal you will use doing that. Most other coal burners i know have smaller houses but larger boilers than i but use more coal than i do. Also i heat to 77 degrees most of the winter in a poorly insulated 3000Sf home with a K-2 and it gets down to minus 10 here. Burn 3 to 4 ton a season.

rdaubert wrote: ↑

Fri. Apr. 12, 2019 9:23 am

Considering everything I've posted, can anyone give me a reason to spend 1000 dollars more on the KA-6?

Many posts in many threads address problems that people have had with underpowered systems, which typically become exposed during cold snaps, when the system is needed the most. Heat loss calculations are fine, but if you read the fine print they don't automatically cover all of the actual temperature and air infiltration issues your house may face. Beyond that, if a boiler is not sized to carry the actual loads (sf of radiation, etc.) to which it is attached, it may wind up falling short. DHW is of particular importance - a 75k boiler might keep up with the heating load of a compact and well-insulated house but likely would struggle to power even a low-volume showerhead in real time. To me it's false economy to "save" a few bucks on a smaller boiler if it means you have to spend a bunch on an indirect or other external DHW storage set-up. And then there are the numerous factors that can cause a coal boiler to perform under its rated capacity - marginal coal, heat exchange surfaces need cleaning, etc.

All of these considerations lead in the direction of sizing a little more generously than might be viewed as "optimal". And I don't agree with k-2's efficiency argument - a larger boiler generally provides larger heat exchange surfaces that promote efficiency when the unit is running, and counteract the standby losses that they also promote. It's an empirical question how much efficiency is gained or lost in any particular situation.

Mike

I agree that heating the hot water makes a considerable difference. Back to back showers laundry and other hot water use can divert BTUs from your heating load. That said i cant imagine a K-4 would not be up to the job. It puts out 30K more than the K-2, about what hot water needs.

On a good day a KAA-4 might keep up with a 2.5 gpm shower with a little left over if it didn't also have a heating load to satisfy. I still vote for something bigger, like a KA-6, that has greater ability to satisfy multiple loads under difficult circumstances.

Mike

rdaubert wrote: ↑

Fri. Apr. 12, 2019 9:23 am

I completed a heat loss calculation and determined that the KA-6 is really unnecessary for my house. That leaves the KFL-6 or the KAA-4. I called Keystoker and they told me that the KFL-6 has the same size boiler as the KA-6, but the same burner as the KAA-4. Also, said that they are most likely discontinuing the KFL-6. I'd rather avoid purchasing a unit that is gonna be discontinued. That leaves the KAA-4 or the KA-6. Heat loss calculation shows that a KAA-4 would work. Considering everything I've posted, can anyone give me a reason to spend 1000 dollars more on the KA-6?

What was your actual heat loss? 35 to 40,000?

I run a ka4 and it has served me well for the last 3 years. I average about 4.5tn\yr for heat and HW. I heat main floor and basement total about 3000sf. I get a lot of radiant heat off the boiler in which I don’t have heat call in the basement zone unless I am hitting the high limit. CI baseboards throughout house built in 1963. Maybe R10ish in the walls and R27 in the attic, Anderson 400s with alum storm windows. We keep the house at no more than 70* bedrooms typically 67/68. Typically burn about 35-40#/day. Big cold I will do about 60.
We have 5 people in the house and lots of wash. Back to back showers, a heat call and dishwasher will put a damper on the HW for sure. Tolerable, yes, endless hot water, no. The extra boiler capacity would be helpful in the k6 but I am not sure if the loss of economy would be worth it? Size is something else to consider between the 6 and 4. My 4 is relatively small for a stoker I know the jump to a 6 is pretty significant.

Food for thought