Summer Project

I have a Harman Mk II in the basement heating the entire house. Throughout the majority of the heating season it does an excellent job of keeping the entire house at a nice even temp. At times that I need to run the stove full throttle or just barley at idle parts of the house get too warm and/or too cold. Given the warm weather here lately I decided to blow the dust off my oil furnace and fire it up for the first time in six years to empty the tank for removal. On first fire of the furnace found the heat exchanger was cracked. Now I have a furnace to cannabilize for parts. On to my project...
I plan to remove the blower, relay and transformer, build a new case for the squirl cage and mount it above the stove. With a few sheets of steel welded to the sides of the stove and ducts tied in I expect to be able to convert my freestanding stove into a forced air furnace and tie into the existing ductwork. I am no stranger to fabrication welding or any of the electrical work required to construct this Frankenstien, the issues I have are HVAC related. I have a few intenional "leaks" in the basement already plus the house is 100+ years old so I have no air intake issues to the basement. Would a system like this work or would I need to figure in a way to run a cold a return from the upper floors to avoid negative pressure? I could always just cut holes in the walls between warm rooms and cold rooms and install power fans, but my motto is if it is woth doing it is worth over doing. I'm open for suggestions and if this works I will post pictures throughout the process so someone else can have fun hacking up a furnace and a stove.

I'm gonna say yes, You should have a way for air in your living space to get back to the source of heat so it can be reheated and sent back into your living space. Firstly because any negative pressure in the basement will cannablize your draft on the chimney and secondly because the whole system will be much more efficient.

For example, my furnace lifts the air temperature that goes into it by 40 degrees (average) - So if my return air from my living space is 70 degrees, the added heat brings it up to 110 degrees, which is being pumped out my warm air ducts back into my living space. If I were to just pull air out of the basement that is say only 50 degrees, the added heat would only bring it up to only 90 degrees for the warm air ducts. PLUS the blowers would be fighting the positve pressure in the living space. I have a friend that just got thru the winter with this kind of arrangement. He used 6 tons of coal. With a good return system I bet he would use 4 tons and be much more comfortable. We're gonna find out next year

How is your heat currently getting from the basement to your first floor?

I use grates cut into the floors to allow the heat to rise up. Also the bathroom is an addition to the original house with a small crawlspace underneath and an access cut into the foundation. I have a fan mounted in the access hole and replaced the shower plumbing access panel with a large register plate that blows air to the first and second floors. The house is a Cape Cod with a finished upstairs btw. The original ductwork for the oil furnace only uses a single return in the room directly above the furnace. Would tying that return into the lower side of the collector around the stove be an efficient loop?

Thats how my cold air return works too. Its one 24x8 inch in the center of the house. I have the basement sealed off from the living area. This way keeps the coal dust and fly ash down there. Its not able to get pumped thru my duct work.

Best case scenario is to have a path of least resistance for airflow, but using your oil furnace's return is far better than none at all. Many secondary heating systems are set up that way.

Do you plan to seal off the open holes in your floor you are currently using for circulation?

Hadn't thought of sealing off the grates in the floor, wouldn't be hard to do though. I could easily place a cold return anywhere, I only plan on reusing the warm air ducts from the existing system. As a side note this really isn't a secondary heating system, the oil tank and furnace is being removed this summer. Though I will need to keep in mind some return because we are installing central air and an electric heat pump for backup heat if we are away from home for an extended time in the winter.

Hi blackdog, thought I would chime in, a couple things entered my mind ( I know, it's a miracle ) Is your home a single story cape or 2, is it an open floor plan? The reason I ask is because I once owned an antique cape in Northern Ma. and the warm air furnace was an obvious retrofit when the center fireplace was removed 60-70 yrs ago and one large cold air return was placed as close to center of the house as possible. This of course was not very efficient and I couldn't understand why my 2nd floor was so cold. I doubt all the testingt that a current HVAC pro does was done then. That was why all the interior doors had a 2 inch gap at the bottom to try to get cold air to the center of the house and down the return. Your local county, or power company (you might have to tell them you're considering going with their fuel or product ) might provide a free air quality test, and various efficiency tests and this may help you decide if you need specific return paths for the air in the home. good luck friend, my coal stove is blowing me out of an 1100 sq. ft. ranch so it also will be going to my basement etc.

Two important things about cold air returns.
1, you will only be able to push hot air into a room, if you remove the same amount of 'cold' air. So you need to remove air or you won't be able to push hot air into a room.

2. Without cold air returns, your stove in the basement is drawing in and heating the coldest air in your house: the cold air off the basement floor.
If you bring 'cold air' returns to the stove, this 'cold air' from upstairs is probably at least 10* warmer than the air off the basement floor, resulting in
a much more efficient heating by the stove..

ALL furnaces have cold air returns, so they reheat the air pulled from the heated rooms, so the air only needs to be raised a few degrees.

Greg L

Hi Guys!

I'm so glad that I clicked on the Summer Project thread! I too have a Harman MkII. I love the thing! I plumbed it into my fireplace 3 years ago. 84 in the family room all winter, 74 down the hall way, and 68 in the bedrooms on the first floor. It does get a might cold, low 60's in the basement. I have a 1600 sq. ft. ranch with a 900 sq. ft partially finished basement. Since my daughter is back living with us in the basement, I have had to turn the oil burner back on. It worked well in conjunction with the stove, but when I filled my fuel tank, It was 750.00. That is more than I normally spend all winter on coal! It just disgusts me!


So, I decided to try a stupid experiment for next winter . I am going to disconnect and push my oil burner out of the way, and put my MkII in its place in the basement under the duct work. I was going to box the stove's blower into the cold air return to pull the cold air down into the basement. I was trying to decide if I should then let gravity work at putting the heat up thru the plenum. After thinking about that for a while, I decided it would probably work better by installing a fan and filters into the plenum in order assist gravity with heating the whole house. My goal is to make the MkII the primary source of heat for the whole house, and kiss the fuel oil companies good bye!

Any thoughts, recommendations, or criticisms are GREATLY appreciated. I think my theory is sound.

Thanks!
Mark

If your going to use your coal stove for primary heat you best check with your insurance company first,, i know it's a bunch of bull but you might want to just ask about it first. I could be very wrong about this but i really dont think they approve of a solid fuel appliance as primary heat source,, hope i am wrong about this.

They don't but, as long as you have a tank with some fuel in it you can call it a secondary heat source. My propane tank has had less than 10% for the last 3 years

Do you guys never go away from home for a couple days in winter? You are planning to remove your "primary" heating systems. I'm all for using coal heat, but it's nice to know the oil burner is there and will kick on if I'm laid up with the flu for four days, or if I go to visit Grandma. (Come to think of it, if I go where Grandma is I won't be coming back, so more than four days' oil should be in the tank.)

I appreciate the feed back. I'm keeping the oil furnace and partial tank of fuel. I'm just disconnecting and moving it out of the way, so it is still available but I don't want to use it. I want to shift to coal and not have to buy anymore oil. So the "primary oil" is still there, but won't be in use.

Any input on the theory?

Submarines, My understanding is that the stove will be "open" in the bassement? and you will be pulling cold air from the living space with the blowers on the stove thru a cold air return? the stove will be positioned underneath warm air plentum? If these conditions are all true and your living space and basement are somewhat tight then my thinking is that the blowers on the the stove will pull air into the basement causing a negative pressure in the living space and a positive pressure in the basement. Since high pressure masses flow towards low pressure masses then your air flow thru your warm air plentum and up thru the duct work will be aided by this effect.

So overall you will have gravity and pressure differences helping to circulate air

Thanks Lightning!

I think that I'm going to have to put a filter in the plenum as well so I don't get the fly ash up stairs.
I also wasn't sure if I needed a fan above the stove in the plenum to suck the hot air and put it thru the duct work.
I think I will try the way have discussed with the slight negative pressure upstairs produced by the stove's blower sucking on the cold air return.

Thanks so much for the input, and sorry for highjacking the thread!

submarines wrote:Thanks Lightning!

I think that I'm going to have to put a filter in the plenum as well so I don't get the fly ash up stairs.
I also wasn't sure if I needed a fan above the stove in the plenum to suck the hot air and put it thru the duct work.
I think I will try the way have discussed with the slight negative pressure upstairs produced by the stove's blower sucking on the cold air return.

Thanks so much for the input, and sorry for highjacking the thread!

Putting a filter in is gonna put another twist on things lol. Since gravity and slight pressure differences will be the main pushers of circulation, that filter is gonna be like a closed door, especially when it starts accumulating dust. The filter will definately compromise your air flow, I do understand your concern about the ash though. You probably will need a blower pushing or pulling air thru that filter. The reason I think this is because if I have a power outage, the first thing I have to do is pull my air filter so air can freely convect on its own so the furnace doesn't get too hot.