Wood Burning Boilers and Furnaces

Q- Why are there no grates or ash pan?

A- The only benefit to grates is perceived convenience.  Wood fires burn more slowly (read completely) on their own bed of coals.  The charcoal phase of wood burning will typically provide about half of the energy output available in your wood .  Grates allow air to permeate under the coals thus burning the heart out of your fire.  Shaker grates and under fire air work great for coal boilers which require 80% under fire air supply.  Our gentle over fire side draft system allows the charcoal to burn to a fine powder yielding the longest burn times per wood species. Very little ash is finally removed. So while the owner of a unit with a grate is carrying his bucket of charcoal filled ashes out in the cold, you will be warm inside with your feet up!



Q- Do I have to let the fire go out to clean the ashes?

A- No!  The typical scenario is to keep the same fire all heating season.  Fine completely burnt ash will accumulate both at the front near the door and to a lesser extent under the secondary baffle path.  A small scoop or two of ash removed each day from the door opening is the ONLY maintenance needed for the firebox.  The best time to remove ashes without letting the fire first go out is when the wood has burned down to a small bed of hot coals, as after a long overnight burn.  Simply rake the coals to one side and remove the underlying ashes.  Repeat the same simple procedure for the other side.  



Q- How expensive is it to install?

A- Less than most other heaters!  If it’s a boiler you will enjoy the fact that no exchangers are needed to add on to an existing system.  Here is a general guide depending on your location (less a chimney)...  Typical warm air installation cost <$1,000.00,  typical indoor boiler installation cost < $2,000.00, and usual outdoor installation cost , $3,500.00



Q- What is the difference between models 200, 400, 500 compared with models 2000, 2500, and 3000?

A-  The Models 2000, 2500, and 3000 have a water jacket surrounding the sides, top and rear of the firebox. The Models 200, 400, and 500 have stainless steel coils in the firebox. The difference between the two is how much radiant heat comes off the unit into the surrounding air. The Models 200, 400, and 500 put about 50% of the heat into the air and the other half into the water. The Models 2000, 2500, and 3000 put about 80% of the heat in the water and only 20% into surrounding air.



Q- What are the holes in the back and front of the models 200, 400, and 500 unit for?

A- The three lines off the back are the hot water heating coils that are in the firebox. One on each side and one on the top; all are one piece in the firebox. All connections are in the back. All three may be used for hydronic heating or two may be used for hydronic and one for domestic water. These coils are ¾” diameter schedule 40 304 stainless steel. They do not require any protection.

The holes on each side of the loading door draw secondary combustion air into the unit. That air is preheated the length of the firebox and delivered behind the vertical baffle into a true secondary combustion chamber. There the hot gases are “flashed off” prior to exiting the unit. This extracts every BTU possible from the wood.



Q- How much firewood will I use?

A- Most owners of Model 500 or Model 2000 units (same firebox) report using about 6 full cords of wood.  We have heard lows of 3 or 4 and highs of nearly 20. The high figure came from folks heating far more than rated capacity and burning year round.  Other factors such as amount of insulation, condition of windows & doors, and heating domestic water play a role, as well.  



Q- How often does the unit need to loaded with firewood?

A-Our boilers and furnaces are designed to be loaded 2 x a day with seasoned hardwood. If it will fit through our generous door openings, you can load it… split or not.



Q- Why is my stove creating smoke and not burning hot?

A- Possible causes may be ashes behind the baffle or chimney needing to be cleaned.  



Q- Do you manufacture ASME stamped boilers?

A- Our Models 200-400-500 and 2500 ASME wood burning boilers have ASME stainless steel water heating coils installed and are approved for installation where ASME rated boilers are required.  The larger boilers (Models 2000-2500-3000) are no longer ASME stamped.  



Q- What is the % efficiency of the units?

A- In regard to efficiency, many of the wood gasification boilers offer “efficiency ratings” in the of “up to” 90% range. Our units as tested by the Canadian government are at 76-77% overall appliance efficiency, which includes heat loss up the chimney. Most manufacturers leave that parameter out of their calculations when talking about efficiency. So our units are very efficient. Burn time at rated heating capacity is designed to be 8-12 hours. Of course, your wood, the building’s insulation as well as other factors will decide the actual time between loading.  Because of this we make no guarantee of burn times.  



Q- I want to heat my pool with wood. Do you have a unit that I can run pool water through or will I need to use a heat exchanger?  Also can this unit be used outdoors?

A- We build a Thermo-Control Model 500 that is equipped specifically for pool heating. One customer is heating a 26,000 gallon pool. Six (6) water heating coils manifold to 1-1/2” all stainless steel. It can be used outdoors. No extra heat exchangers required as pool water can be run through it (all 304 stainless). We also build larger pool heating units for pools 40,000 gallons and more.  



Q- Is the model 500 wood fired boiler compatible to use as an add-on to an oil-fired boiler with one pipe steam heating?

A- Yes, it is compatible with low pressure steam systems. We have done this for over 35 years.  The installation requires that the unit have continuous water flowing - note the circulator pump and the fact that inlet and outlet must be below the water level.  A 30 lb pressure relief valve must be installed on the line.  The pipes are ASME rated at 150 lbs.  The low pressure steam system normally runs at 3 - 5lbs.



Q- I have an existing oil fired boiler that heats the house with forced hot water and the domestic water through a second coil. If hooked into the furnace, do the wood boilers require additional heat/water storage? And is the water that the units hold for heat or domestic use?

A- The Models 200, 400 and 500 require an additional storage tank of minimum 40 gallons. The Models 2000, 2500 and 3000 do not require additional water storage. The water that the Models 2000, 2500 and 3000 hold is for hydronic heating (12PSI-14PSI)



Q- Are your units equipped to burn coal?

A- Our units are not currently equipped to burn coal as that requires a grate system that we are not currently offering.  



Q- What type of insulated pipe do you offer?

A- The pex-al-pex pipe that we carry is Kitec (1” ID) with an aluminum oxygen barrier. The price is $11.00 per foot for the two line, four insulated wrap in a 4” diameter sleeve. That is the best pipe to use in a closed (pressure) system.



Q- What is the difference between pex pipe and pex-al-pex pipe?

A- Within the outdoor wood furnace industry there are mainly two types of pipe used, pex and pex-al-pex.  The basic pex pipe is cross-linked polyethylene.  Most commonly, crimp rings are used to pinch the pipe around the brass fittings. Compress fittings are also available.  Pex-al-pex (also known as pex-al, pexal, or p.a.p.) is a five layer pipe composed of plastic, adhesive and aluminum.  Crimp and compression fittings are both available for pex-al-pex pipe.  When used with water at high temperatures, such as outdoor wood furnace applications, expansion is to be expected.  Regular pex has a very high expansion rate.  This expansion creates dramatic droops in the installation.  A nice, neat set of lines looks like limp noodles.  Aesthetics aside, this expansion can also cause problems.  When pex line is used in underground pipe the expansion becomes compressed.  The extra line puts pressure on the pump and fittings attached at either end.  Pex-al-pex lines have expansion properties similar to copper.  When they are running hot water the expansion is minimal.  Lines maintain their shape and underground runs do not put extra pressure on pumps or fittings.  Pex-al-pex lines also have a full 1 inch inside diameter (ID) compared to 1 inch pex lines that have an ID slightly less than 7/8 inches.  This difference in ID makes a big difference when transferring BTU with hot water.  Transferring the proper BTU through the water lines is crucial to the performance of the heat exchangers used in an outdoor wood furnace system.  Limit the ID and the BTU transfer is reduced significantly.  



Q- Is your model 500 boiler stove suitable for heating a house via hot water baseboard?

A- The Model 500 Boiler is well suited for heating the house via hot water baseboard. The Thermo-Control is both efficient, durable, and a good value.



Q- Do your products meet EPA standards?  

A- Indoor wood burning boilers and furnaces are EPA exempt.  Usually that question is tied to the efficiency of the units.  The Thermo-Control boilers incorporate the combination of natural draft and a separate secondary combustion chamber for efficiency. The two specially designed combustion chambers featuring separate primary and secondary pre-heated air supplies contributes to a longer lasting, cleaner burn. Wood and wood gases are burned more efficiently because of the airtight gasket door, pre-heat chamber for hotter combustion, downdraft baffle system and secondary air supply. The downdraft forces the smoke and gases down over the flames, squeezing every BTU possible out of it before sending it up the chimney.



Q- Are they legal for sale in all states?

A- Yes, they have been tested and listed to applicable UL standards and others by accredited independent labs.  Check your local codes before purchasing.    



Q- Do your units require provisions for make up air?

A- We do not have provision for make up air with our units… remember that they are natural draft and pull very little air out of the house.  Make up air can be provided in the vicinity of the front of the unit if you really need more air.



Q- I would think that water going through this stove would be boiling at exit - would not pipes going to the present water heater (80 gal.) burst from the intense boiling water?
A- The answer to that question is proper design and construction. In a closed (pressure) system the water will not “boil” in the firebox.  The system is designed to be run at 180° F and works very well when properly installed.  Over 35 years of no bursting pipe
s.



Q- How does it hookup to my heating system? I have a new ultra high efficiency boiler. Do I just heat up the return lines which go back into the boiler?

A- Correct. By "pre-heating" the returning water, the existing aquastat is satisfied and the gas or oil burner will not fire.



Q- Is there an additive to put into the water chamber that helps with rust/etc. that you recommend?

A- In a closed system it is unnecessary to have a rust inhibitor although some choose to use it anyway. Our owner’s manual talks about it because some customers choose to open the system (atmospheric pressure) and operate the unit that way. When water goes over about 140 degrees F the properties change and oxidation ceases in a closed (12-15PSI) system.


Q- What is the standard payback on a unit?

A- The standard payback is usually between 3-4 years. That means that the proper investment can yield somewhere between 25 -33% return. Too bad it's a limited amount of money you can, or need to, put into your home's heating system. And you're not really investing in heating per se, you're investing in avoiding energy costs and your home's comfort (and value).


Q- Can you run the 200/400/500 without water in the coils?

A- Yes. It is not recommended for a long period of time. DO NOT leave the coils capped while running the unit dry.


Q- Can you run the 2000/2500/3000/4000 without water in the water jacket?

A- No. You absolutely should NOT run these units without water in the water jacket.


















F.A.Q.

(518) 296-8517, PO Box 600, 129 Goodfellow Lane, Howes Cave, NY 12092

sales@nationalstoveworks.com


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