Monday, September 25, 2017

Six tips to buy the right pellet stove

Retailers say BTU output can be most confusing issue

Glenn Robinson is one
of many retailers struggling
to help consumers avoid
relying on manufacturer
claims about BTU output.
Glenn Robinson has been selling and installing pellet, wood and coal stoves in Pennsylvania for 11 years, and one of the biggest problems he faces is sizing the stove.  “I became tired of false information from manufacturers about how many BTUs they claimed their stoves put out” he said in a recent interview.  “Customers see these exaggerated BTU numbers from a small stove and think it will heat their home, but it won’t.  The result is that the stove is undersized and there is premature wear and tear.  One model from a big name brand would only last for 3 – 4 months before needing repair or even full replacement,” he said.

Glenn is not alone in identifying exaggerated BTU listings as one of the biggest problems consumers face in buying a stove.  Scott Williamson, a Massachusetts pellet installation and repair technician says that he sees stoves “all the time that are being run on high 24/7 and pellet stoves just aren’t designed to do that.”  Both installers say that under sizing of pellet stoves is one of the biggest problems, and urge customers to consider larger (higher BTU output) stoves if they live in average size homes in the northern half of the country and plan to use the stove a lot.

Buying a pellet stove can be a confusing process for consumers. Retailers are likely to push the brands they sell and manufacturer websites don’t tell the whole story.  Objective, third party reviews are rare and often outdated.  Consumer Reports did a pretty good review in 2009 but used very limited criteria and didn’t test for durability.  The Alliance for Green Heat (AGH) also undertook third party testing in 2015 and issued a detailed online report on some issues including BTU output, maintenance and efficiency. (Like Consumer Reports, AGH conducted completely independent testing by purchasing all the units and doing all of our own testing.)

This blog identifies and discusses six rules for consumers to keep in mind when buying a pellet stove, with a focus on sizing.  This is not an exhaustive list but it’s a good place to start: 1. Don’t undersize, 2. Beware of cheaper stoves, 3. Look for range of heat output, 4. Understand maintenance requirements of the stove, 5. Look for cleaner stoves and 6. Beware of stoves with no efficiency on the EPA list
AGH tested six popular pellet stoves.
Almost all performed well during
intensive 30 day testing, but did not
live up to some manufacturer claims.

Pellet stoves can be a very effective and affordable way to provide primary or secondary heat for your home without the smoke that wood stoves often create in the hands of the typical user. Wood stoves require lots of work on the fuel side of the equation, but pellet stoves involve more work on the appliance side of the equation. 

The Alliance for Green Heat also monitors advertising of pellet stoves and has found over the years that the great majority of companies vastly overrate the amount of heat their stoves put out.  The EPA list of certified wood and pellet stoves is not perfect but it remains the best source of BTU output for consumers. 

Most EPA-certified pellet stoves are listed as producing a maximum of 25,000 – 40,000 Btu and minimum of 7,000 – 13,000 Btu. The average pellet stove on the EPA list, according to data provided by third party test labs, put out a maximum of approximately 31,800 Btu and a minimum of approximately 10,050 Btu. 

The stove with the highest maximum Btu on the EPA list is the Harman P68 at 53,500 Btu (advertised at 71,200 Btu input).  When a stove manufacturer lists Btu input, it refers to amount of Btus in the fuel, if you were to get 100% of those Btus into the room.  But the average pellet stove is around 73% efficiency, which means you will get 73% of the fuel’s potential heat into the room.  (This is similar to the AFUE – the annual fuel utilization efficiency – that is used on gas and oil boilers and furnaces.)

The stove with the lowest maximum Btu is the Thelin Gnome pellet stove that puts out up to 9,000 Btus.  However the company advertises three times that - 27,000 Btus - without any explanation.  Manufacturers usually exaggerate Btu, thinking that it will make their stoves more attractive, but in the case of the Thelin Gnome, there are people looking for stoves to heat very small places and the exaggerated Btu output may make them think even the Gnome is too big.

Here are six critical things for consumers to keep in mind when purchasing a pellet stove:

1.       1. Don’t undersize. If the stove is going to be your primary heat source you will likely need a medium or large pellet stove, even if a smaller unit advertises high BTU output.  Ignore BTU numbers on manufacturers websites and literature and check the EPA list.  The maximum output for pellet stoves is in the 30,000 – 50,000 range, enough to heat all or most of a small or medium house in most climates. “Don’t plan to run the stove all the time at its highest setting,” warns Scott Williamson “or you will be calling someone like me to fix it quicker than you think.”  When we tested six popular pellet stove models, we calculated an output of no more than 21,000 BTUs, far below what the EPA listed and even farther below what manufacturers claimed.

(It is possible to oversize the stove and that can be a problem, but is not nearly as common as under sizing.  For example, the Harman P68 is notorious for being installed in small areas like mobile homes but they gunk up when they aren't allowed to get up to temperature for a bit before they shutdown,” says Scott Williamson.)

2.      2. Beware of cheaper stoves. There are some good budget wood stoves on the market, but with pellet stoves, you are more likely to get what you pay for than with wood stoves.  “If you want a reliable stove that puts out a lot of heat, we urge customers to ignore pellet stoves under $2,500,” says Glenn Robinson.  Scott Williamson generally agrees but has seen some basic stoves like the Pel Pro and Englander hold up pretty well.

3.      3. Check for range of heat output.  Most stoves can put out about 3.5 times more heat at their highest setting, compared to their lowest.  Some stoves have a tiny range, putting out only 1.5 times more heat at their highest setting.  If you live in a more moderate climate, in the early fall and late spring, you may want just a little heat, and still have the capacity for much greater heat output on the coldest days and nights of winter.  All other things being equal in a stove, you may want a stove with a larger range of heat output and you can check the range of all stoves on the EPA list of certified stoves. In our tests, we found that the Enviro M55 insert ran continuously for an impressive 49 hours on its lowest setting with a tested hopper size of 60 pounds and it ran for 22 hours on its higher setting.  However, with a 37-pound hopper, the Englander 25 PDVC only rain for 15 hours on its lower setting and 13 hours on its highest setting, indicating a very low turn down ratio.


4.       4. Understand maintenance requirements. If you don’t clean your stove regularly and have it professionally serviced once a year, don’t expect high BTU output.  Most consumers get subpar performance from stoves and have to repair them more often because they are not maintaining their stoves according to the owner’s manual.  Pellet stoves are not like wood stoves: they have lots of moving parts and need cleaning of the burn pot and inside the stove on weekly, and depending on the stove, a daily basis.  Pellet stoves that are not cleaned regularly can lose 10% or more of their efficiency – and their heat output, and lead to costlier repairs. Understand the daily, weekly and annual maintenance requirements from the start and don’t put them off.  When we tested six popular pellet stoves, we found that the three more expensive ones (Harman, Quadra-Fire and Enviro) could go for a week or more without cleaning the burn pot.  However, the Englander, Ravelli and Piazzetta needed daily burn pot cleanings.

5.       5. Look for cleaner pellet stoves.  Pellet stoves are far cleaner than wood stoves, even if they both have the same particulate matter in grams per hour.  Particulate matter is the tiny stuff that smoke is made out of and pellet stoves should not have any visible smoke after the 3-minute start up.   The average pellet stove used to put out about 2 grams of particulate per hour.  But since the new EPA regulations took effect in 2015, the average pellet stove emits about 1.3 grams per hour that makes pellet stoves more suitable in more densely populated suburban and even urban areas.  Choosing a cleaner pellet stove means a cleaner flue pipe and cleaner air around your and your neighbors’ homes.

6.       6. Beware of stoves without an efficiency on the EPA list. As with BTUs, manufacturers routinely exaggerate the efficiency of their stoves on their websites, so if efficiency and saving money is important to you, check the EPA list of stoves for efficiency ratings.  The problem is some companies still haven’t reported their efficiency to the EPA, so you may only want to purchase a stove that has an efficiency listing on the EPA list.  Pellet stoves with listed efficiencies range from 58 to 87% efficiency, but those not listed could be even lower, drastically increasing your heating costs.

The EPA list includes some slightly exaggerated efficiency numbers, but they are not nearly as exaggerated as manufacturer websites and literature. The EPA used to allow companies to calculate efficiency based on a default of 78% efficiency, even though most pellet stoves are below that, explains Ben Myren, who runs one of the stove test labs approved by the EPA. The result is a 5-10% exaggeration of some stoves on the EPA site, something that the EPA has not publicly acknowledged. (Some incentive and change out programs - Maryland, Massachusetts, New York and Oregon - require that the stove have an efficiency listed on the EPA list to get the full rebate.)


Appreciating these six factors are likely to help you make a better decision, but we also encourage consumers to rely on feedback from friends, neighbors and others who own pellet stoves. One site that can be helpful for research is hearth.com.  

A final note of caution is to take advertised hopper size with a grain of salt.  Most manufacturers also exaggerate hopper size.  Of the six models we tested, Harman and Ravelli exaggerated their hopper size by 15 – 18%, while Enviro didn’t exaggerate at all.  Choosing a stove with an advertised hopper size of 50 – 60 pounds can be a good idea, as it means the hopper will likely hold 45 – 55 pounds and you can empty an entire 40 pound bag in it when its low.

Wednesday, August 30, 2017

Lessons in building a 120-Watt thermoelectric wood stove

Guest Blog: We are reposting a 2012 blog from Instructables by Tecwyn Twmffatt at Goat Industries. It describes an early effort to build a thermoelectric wood stove.  This blog is part of a series of blogs providing information for the 2018 Wood Stove Design Challenge.

Introduction: Thermoelectric Power Generation (TEG) 

These videos document my first attempts at generating electricity from a thermoelectric peltier device in 2012. The TEG that I used is a high powered unit able to withstand high temperatures and specially made for electricity generation.

In terms of instructions, I don't think many people would want to build the 10 TEG system as it was ridiculously expensive, so I'm putting in a section for creating the 1 TEG arrangement, which is relatively easy and low cost.

Step 1: Part 2 of 3 

 


A ten unit Thermoelectric generator system is shown being constructed and then fitted to a wood burner. The theoretical maximum output is 200 watts. The video shows how the generator was put together and how the wood burner was modified to get maximum heat through the TEGs. The TEGs themselves are able to withstand a constant 325 degrees C on the hot side and require plenty of heat to get the 20 watts that each of them are capable of producing.

Step 2: Part 3 of 3 

 


In part 3 we successfully generate a significant amount of energy from the woodburning stove. In the first session, a circulation pump, a fan and 10 x 10 watt flood lights are powered up. In the second session, we attempt to get a more balanced load wired up to the tegs and measure a noticable increase in power output. The 10 tegs are wired up in 2 parallel strings and, from the manufacturer's specification, the optimum output voltage is 14.4v . The nearest that we manage is 13.8v, at which we generate 120 watts. The specifications suggest that 200 watts is possible when the load is matched.

Step 3: Full Playlist


31 Minutes of Thermoelectric video heaven!

Step 4: Creating the 1 TEG Generator


Here we are going to build the single TEG generator shown in the first video.

Step 5: Tools and Equipment  


Parts: 


Thermoelectric power generator TEG module (GM250 449 )
...... buy direct from China at: www.thermonamic.com/
Aluminium block 102 x 115 x 20 mm
Steel block 102 x 115 x 10 mm
1/4" BSP blanks x 6 of
1/4" BSP male stud push fit pneumatic fittings for 10 mm pipe x 2 of (See photo above)
5 mm Hex bolts x 40 mm x 2 of
25 litre water butt
OD 10 mm ID 8 mm nylon pneumatic pipe
12V water pump
12V LEDs, 1 watt x 20 of

Tools: 

1/4" threading tap
5 mm metric coarse threading tap
Drill 11.5 mm
Drill 5.5 mm
Drill 4.2 mm
Drill press
Torque wrench
MIG welder
Plasma cutter / Grinder with cutting discs
GM250-449-10-12.pdf

Step 6: Drilling and Tapping the Cooling Block


Use the engineering drawing to produce internal coolant passage ways in the aluminium block. I ended up drilling all the way through to the other side and using more of the 1/4" blanks.

Connect the 1/4" pipe fittings to the block and plumb in the pump. Add antifreeze to the water in the water butt if it's likely to get cold at all.

To create a 'sandwich' with the hot block (steel block), the TEG and the cooling block, drill and tap holes in the steel block for the 5mm bolts.

Weld the hot block into the side of the wood burner and recreate the TEG sandwich, tightening the bolts up with a torque wrench (see attached file).

Connect up LEDs on the TEG, turn on the pump, light the wood burner and off you go!
TEGinstallationandspecifications01.pdf

Step 7: 10 TEG Layout



If you really must build the 10 TEG generator, the photo above shows what is involved. I have got CAD drawings, PCB drawings etc. If anybody is interested. Not for the faint hearted!

PCB 03.pcb
PCB 01.zip
CAD files 02.zip

Friday, August 25, 2017

Adventures in masonry stove testing from 1988 to 2017

by Norbert Senf, 
Chair of the Masonry Heater Association Technical Committee


Left to right: Mark Champion (in his 
VT test lab), Boris Kukolj (Tulikivi), 
Chris Prior (MHA President), Norbert 
Senf (blog author)  and Jean Francois 
Vachon (soapstone stove builder). 
Photo credit: Mark Seymour.
EPA started regulating wood burning stoves for particulate (PM) emissions in 1988. Regulation was limited to airtight heating stoves. Masonry heaters were not regulated, the stated reason being that they were likely to be clean burning.

In Europe, only carbon monoxide (CO) emissions were regulated. CO is easy to measure, however PM can be very tricky. Wood smoke includes  compounds that will only be captured by a filter if you cool them down and condense them. This is done in the laboratory by mixing them with air in a dilution tunnel, and this is thought to simulate what happens in the ambient air in the real world.

State and county air quality authorities soon started to address wood smoke, and would often pass a generic local regulation that banned all appliances except those that were EPA certified. We, the fledgling Masonry Heater Association (MHA), decided to seek EPA certification.

Although we "knew" that masonry heaters were cleaner even than EPA stoves, nobody had ever measured the PM on one with the dilution tunnel method. With funding help from the Wood Heating Alliance (now HPBA), we were able to participate in a $100,000.00 test method development project for masonry fireplaces and masonry heaters. The project took place at Virginia Polytechnic Institute (VPI) in 1989 and was headed by Dr. Dennis Jaasma.

The results were interesting, with some surprises. EPA did not accept the proposed test method. We immediately realized that we needed do a lot more testing,  and that we would need to develop the capability to do it ourselves.

We were fortunate in being able to arrange for training with OMNI-Test, one of the leading EPA-accredited certification testing laboratories, then and now. OMNI developed a training session for us that took place in September 1996. It included presentations by regulators, an emission chemistry expert (Dr. Jim Houck),  and laboratory testing personnel. Dr. Stockton (Skip) Barnett showed us the low cost portable dilution tunnel that he invented, known as the Condar. He developed it while working for the Condar Company. It was widely used at the time by the major stove manufacturers for in-house testing to develop their certified  stoves.

The attached Powerpoint, Repeatability of Cordwood Combustion Particulate Measurements,  presents a summary of the work we have done at the Masonry Heater Association to calibrate the Condar against the EPA Method 5G laboratory dilution tunnel. It includes a close look at the PM testing repeatability issues,  a major discussion point over the years. We have recently completed 2 cordwood studies, using very carefully matched loads in a masonry heater. Repeatability was within plus or minus 15% - 25%, depending on the ignition method. With crib fueling, we were able to get within 10% repeatability on PM, and within 1.5% repeatability on CO.