Harman Mark 3 as Boiler Supliment?

Looking for guidance

I have a eight zone, eight section Weiler Mcclain oil burner with 1.2 gpm nozzel its around 285K BTU with cast iron 10 large radiators.(large volume water in system 60 gal plus) boiler is already piped to accept add on boiler in series with return header.

Heating around 4,500 sf of 110 year poorly insulated old house.

I realize this isn't Ideal situation but what are the pitfalls?

Due to the price and avalibilty of coal boiler and my 3,000.00 dollar budget for this year!

I am looking at adding Harman mark 111 (92 k btu) with Two hot water coil to supplement my existing boiler.

This hand fired stove would be run at max for the 12 hours a day that I am not home.

My plan is to use a a safty and a temperature switch on the outlet of the hot water coils and add a circulator dedcated to coal boiler from the supply and back to the return header.
This way if no zone is not calling for heat I can use the boiler as a heat storage.

Should I add a storage tank instead of using the Boiler?

I have chart recorder with switch output so I can force on a zoneor more in case of high water temperature.
I can do all the work my self

Thanks for the comments
Doug

Why not get a much larger coal stoker boiler and use the existing oil burner as backup, or to supplement the coal boiler on the coldest of days. Several good coal boilers brands to choose from.

Blackdiamonddoug wrote:Heating around 4,500 sf of 110 year poorly insulated old house.

You are going to want a boiler with this deal.

Contact forum member Matthaus via Private Message [PM]. He is refurbing several boilers, he may have one that will work for you...

The Mark III, while a very good hand feed stove will do a much better job heating a space or several rooms than it will heating water.. there just isn't enough surface area on even two coils in a stove to do a significant job heating water.. the coils just pull enough heat to keep a hot water tank hot.. the coils do not turn a stove into a boiler... just not the right design.

Greg L

I have quite a lot of experience with this and all I have to say is save your money. The Harman coils work great for making a tank of hot water if you are not in a hurry. The heat absorption area of the coils is designed for make up domestic hot water, they will not provide 10% of the heat needed for home heating. Do what Greg says and shop for a used boiler you will be much happier and warmer.

Doug, I too looked into this with my Mark III. I installed a single loop coil in it to heat domestic hot water in a 30 gallon holding tank. It worked good, actually it worked too good and I wasn't able to use all I heated and the temp pressure valve on the tank would blow open a couple of times a day. So, I piped it into a toe kick heater in my kitchen where the fan opens up at 140 degrees and that worked great. I then hook it up to my entire house which is a 200 year old three story colonial house. It heated my entire house all winter to 72 constantly. But there was not enough heating capacity for my domestic hot water anymore. I have all radiant heat in my house where the water temps needed are much lower than what cast iron radiators need. I don't believe you would be able to do this with your setup. I need from 90 - 110 for water temps for radiant whereas you are going to need a minimum of 180. Like others have said even though the Mark III is a great coal burner it was not made to do what you want. If I were in your shoes and knowing what I have learned I would lean more toward a coal boiler which is made to do just what you want.
Tom

Hi all
Thanks for the all the advise I am now looking for a used coal boiler.
Thank you all