Convert multiple LPG Furnaces to Hydronic Coal

 
north jersey
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Post by north jersey » Sat. Jun. 29, 2019 6:39 am

I'm about to make an offer on a house that features three LPG furnaces. The real estate agent felt this feature of the house was a selling point, but I don't want to pay for propane, and I can't really operate three coal furnaces (let alone run chimneys for them).

How well do hydronic to air heat exchangers work, and do you think they would be a good solution coupled with a coal boiler?


 
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Richard S.
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Post by Richard S. » Sat. Jun. 29, 2019 7:36 am

Large furnaces are available. Is there something I'm missing as to why you would not install one?

https://leisurelinestove.com/product-category/furnaces/

 
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Post by coalkirk » Sat. Jun. 29, 2019 9:02 am

Water to air heat exchangers work very well. By the way real estate agents are like politicians. If their lips are moving they are probably lying. Calculate the BTU demand for the home and by a coal boiler to match that demand. Might as well throw in an indirect water heater also.

 
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Post by Rob R. » Sat. Jun. 29, 2019 9:24 am

Water to air heat exchangers work very well...assuming they are sized and installed correctly.

If you can use a single coal furnace, that would be the simplest solution. However - if there are three existing LP units, I am guessing they are spread out in different areas of the home?

 
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Post by Pacowy » Sat. Jun. 29, 2019 9:45 am

coalkirk wrote:
Sat. Jun. 29, 2019 9:02 am
Might as well throw in an indirect water heater also.
If you're talking about a boiler big enough to do the work of 3 furnaces you could also consider a DHW coil in the boiler.

Mike

 
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Post by north jersey » Sat. Jun. 29, 2019 11:20 am

I have an indirect I would bring with me. Can't use a single furnace because the furnaces are located on different floors. I think this time I might try to find a boiler with an ash auger this time. I seem to recall a Canadian manufacturer has one in production. Any recommendations for an exchanger?

 
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Post by David... » Sat. Jun. 29, 2019 12:00 pm

Two of my heating zones are hydro air and my coal boiler doesn't mind them.

David


 
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Post by Pacowy » Sat. Jun. 29, 2019 1:17 pm

north jersey wrote:
Sat. Jun. 29, 2019 11:20 am
I have an indirect I would bring with me.
There's no assurance that an indirect sized for a smaller boiler, like a VF3000, will produce DHW as effectively as a coil in a larger boiler. Suggest you check the numbers.

Mike

 
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Post by lsayre » Sat. Jun. 29, 2019 1:48 pm

I recently learned that a rather typical HVAC rule of thumb is: 1.4X home heat loss calculation BTUH = required boiler size in terms of net BTUH output. A boiler sized by this method is claimed to meet the "25 year test", meaning it should theoretically be adequate to heat your home on the coldest anticipated single day that is likely to occur within any given span of 25 years, presuming a heat loss calculation taken for the "99% design temperature" in your locality.

So for example: If your homes official heat loss calculation is 34,500 BTUH, then a boiler capable of delivering an honest net output of 48,300 BTUH should cover all bases except the DHW base. Do not be surprised at how low an actual home heat loss calculations BTUH will be. When people hear the value they are generally shocked. Quite often the figure comes in at only about 1/3 of the BTUH input rating of an older homes current furnace or boiler.

The last I heard was that the going rate for a quality home heat loss calculation is in the neighborhood of $180.
Last edited by lsayre on Sun. Jun. 30, 2019 7:09 am, edited 2 times in total.

 
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Post by Pacowy » Sat. Jun. 29, 2019 4:46 pm

I think trying to work directly from heat loss to boiler sizing here overlooks issues related to the distribution networks of the existing furnaces. If properly engineered, each network was designed based on the output of the corresponding furnace. If the new water-to-air heat exchangers don't basically replicate the current furnace outputs, you run the risk that the system will not work as well as it does now, irrespective of the heat loss computed by some spreadsheet. And if the new heat exchangers do replicate the current furnace outputs, those are the btu's the new boiler needs to be able to cover, plus a pickup factor, plus an allowance for DHW and any other attached loads. A boiler that can't carry the loads to which it is attached is problem waiting to happen.

Mike

 
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Post by Rob R. » Mon. Jul. 01, 2019 6:22 am

Pacowy wrote:
Sat. Jun. 29, 2019 1:17 pm
There's no assurance that an indirect sized for a smaller boiler, like a VF3000, will produce DHW as effectively as a coil in a larger boiler. Suggest you check the numbers.

Mike
If it is the indirect he bought a few months back, it is large enough for a moderate apartment building.

 
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Post by coaledsweat » Mon. Jul. 01, 2019 7:23 am

Keep in mind a boiler's life span is exponentially longer than that of a furnace.

Water to air heat exchangers are very efficient, but they must be multi pass in this application.

 
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Post by coalkirk » Mon. Jul. 01, 2019 8:14 am

A point to remember also is that the multi-pass coil should be plumbed so that the feed enters the coil so that the air passes over the hottest water last. Mine was hooked up the other way for years. Made a big difference in air temperature when it was corrected.

 
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Post by lzaharis » Mon. Jul. 01, 2019 8:56 am

north jersey wrote:
Sat. Jun. 29, 2019 11:20 am
I have an indirect I would bring with me. Can't use a single furnace because the furnaces are located on different floors. I think this time I might try to find a boiler with an ash auger this time. I seem to recall a Canadian manufacturer has one in production. Any recommendations for an exchanger?
========================================================================================================
About the Canadian coal stokers;

If you mean the Portage and Main coal stoker boilers they are coal stokers that are designed to be used outside of a residence.
The Portage and Main ML30 model is 400,000 BTU with a water volume of 120 gallons and the ML36 is 600,000 BTU with a water volume of 190 gallons.

If you want a larger animal the smallest All Canadian Heater coal stoker boiler is 500,000 BTU with a pot stoker that has to be placed in its own building. An ash auger can be supplied that would be long enough to reach into a dumpster or roll off container.

The folks at All Canadian Heaters are very nice to chat with and the vertical fire tube design is simpler to clean and it has diffusers in the fire tubes to extract as much heat as possible before the flue gas is ejected in the stack.

You could do the same thing with a pair of EFM DF520 stokers with smaller plumbing.

 
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Post by Pacowy » Mon. Jul. 01, 2019 9:42 am

There are several old conversion stokers that provided automated ash removal, and I used one for years. It's important to remember that you still have to be able to handle whatever container the ash remover is filling. Anything bigger than about a 20 gallon trash can will tend to be unwieldy, especially if stairs are involved. And even though mine worked well, it's still a mechanical device doing difficult work, subject to wear, breakdowns, etc.. In general, unless you have a unique situation, I would lean toward plain old ash pans or an ash pit.

Mike


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