Subject: Re: Fw: Your Masonry Heater manufacturers...

Hello

Several studies have been done on outside air here in North America, and to date no-one has been able to demonstrate any benefit. Refer, for example, to

http://www.woodheat.org/outdoorair/outdoorair.htm

http://mha-net.org/msb/html/papers-n/airreq/cmhc-rep.htm

If there is any European data that demonstrates any benefits from outside combustion air supplies (as opposed to room makeup air), I would be very interested in evaluating it.

Best ....... Norbert Senf

--------------message separator--------------------------

(above message was also copied to MHA executive and John Gulland, and John Gulland also replied.)
---------------------------------------------------------

From: Chris "Smith"

Obviously I've got you all very bothered...so I've got you thinking! you're reading studies w/o understanding them and their fallacies! Just because they did a study doesn't make it law! This is engineering 101.

John, Please educate me! A simple questions I keep repeating...and NO studies, if you can't describe it yourself your you don'tknow it. Where does that combustion air come from?

What about all those exhaust fans, the dryer, the kitchen hood, both bathrooms...do those interact with the masonry heater? What if you ran all of them at the same time? Why are the Swedes putting OA sources into their units?   

---------------message separator------------------

To: Chris "Smith"
From: Norbert Senf

At 1122 AM 2001-08-28 -0400, you wrote

Norbert,
No offense...but studies on outside air? Is that a Canadian study where someone spends two days living outdoors with a case of Molsens? Do you have an ASHRAE reference?

Combustion air is unconditioned air used solely as makeup air for a combustion process, and you don't get combustion w/o it! Typically a small 4" diameter pipe to an outside wall, with a wind shield, bird guards, and anti-siphon devices to prevent a vacuum effect during high wind.

Room makeup air is CONDITIONED AIR (you pay to condition it!) that can air transfered from other rooms to another room to be returned to the air handler, or fresh air into the air handler to account for air exhausted to the outdoors elsewhere, etc.. If you want to feed conditioned air to your fireplace go right ahead...your paying for it!

No offense, Chris, but if you read my study for CMHC you will note that the air consumption from a large masonry heater is 10 - 15 litres per second during full burn. The BTU's required to bring that air from outside temperature to room temperature are negligible if you do the math. Furthermore, if you bring the same air directly to the firebox instead of through the conditioned space, you still have to heat it up, except that now you are using cold air for combustion - never a good idea.

Please don't confuse a masonry heater with an open fireplace, which has air consumption in the 200 litres/second (400 cfm) range

Your "Woodheat study" noted "Those air intakes which were connected to the circulation air plenums", thats like hooking up your domestic water to your sanitary waste line...dangerous...very...very very, and that's not a fresh air source, its your living space air! Your now getting into many >more aspects of airflow in the home than you realize. Depending upon how the ductwork has been constructed (tighness, configuration/pressure loss), status of the fan, and location of all ductwork I would characterize that configuration as attempting to poison the homes occupants.

Please note that this study was done in a lab setting with available off-the-shelf zero clearance fireplaces, 15 years ago. Zero clearance fireplaces and masonry heaters are completely different animals.

Nevertheless, neither this study nor another one done by Dr. Dennis Jaasma at the Dept' of Mech. Eng. at Virginia Tech demonstrated any lessening on fireplace spillage susceptibility due to outside air.

If you have any data to the contrary, ASHRAE or otherwise, I'd love to see it.

Norbert Senf

--------------message separator---------------

From: Chris "Smith"

Norbert,

So your saying that your CMHC study found 21-32 CFM combustion air needs is not significant enough to warrant a fresh air source? And that 145 MBH (thats 32*70*1.08*60, the math) in makeup air heating is insignificant to worry about, boy your heating cost must be low! You're still breathing CO!

Litres/Sec CF/Sec CFM

15 0.53 32

10 0.35 21

200 7.06 424

Enough..best wishes, good day!

Chris "Smith", PE, CIE
"Company name deleted", LLC
Diagnostics & Performance Testing Group
"address"
"phone"
"fax"
"website"

------------------------message separator----------------

To: Chris "Smith"
From: Norbert Senf
Cc: John Gulland

Subject: RE Fw Your Masonry Heater manufacturers...

Chris

Don't forget that a masonry heater is a batch fired appliance.

The 20 cfm is for 2 hours out of a 24 hour heating cycle. For 22 hours out of 24, the flue damper is closed and there is no air flow.

As I mentioned, you are using the firewood to heat the air one way or another, whether it comes in directly to the firebox, or through the room.

Don't know where your CO reference comes from. This presumably relates to the issue of combutsion product spillage caused by, for example, building depressurization. If you took the time to analyze the ORTECH study, you would realize that introducing the combustion air directly to the firebox had NO (I repeat, NO) effect on spillage susceptibility, as I mentioned. This is counterintuitive, I know. However, this and the VPI study are the only test data that I am aware of.

The way to prevent spillage is to keep the room pressure above -5 pa by making sure that your exhaust appliances have enough makeup air.

Again, if you have any data to the contrary, let me know.

------------message separator----------------------------

To "Norbert Senf" mheat@mha-net.org
From: Chris "Smith"
Subject: RE Fw Your Masonry Heater manufacturers...

Norbert,

You and John from what I can determine are Masonry Heater salesmen, you sell. I'm an engineer, I troubleshoot, fix, design, and commission buildings. I've worked on multi-million SF buildings, always with an answer. Your article is from Woodheat.org, an organization promoting your industry. The CMHC study was about fireplaces, not masonry heaters, like you said different animals. The CMHC study makes some points which are true for fireplaces, but your "Woodheat.org" website is twisting those points and using them improperly. It states one point but fails to look at the other aspects. A hole in a wall is not a fresh air source, its a leak, a big leak that was not engineered.

Chris "Smith", PE, CIE
"Company name deleted", LLC
Diagnostics & Performance Testing Group
"address"
"phone"
"fax"
"website"

------------------------message separator---------------

To: Chris "Smith"
From: Norbert Senf

Subject: RE Fw Your Masonry Heater manufacturers...

Chris

I have based my conclusions on the data from the measurements in the ORTECH study, the VPI study, and the study that I did for CMHC in order to qualify masonry heaters for inclusion in the Canadian R-2000 standard.

So far, you have given me your opinions and your qualifications.

I studied mechanical engineering at university, as well. I don't recall at any point being taught that opinions take precedence over measurements.

Again, show me some evidence that outside combustion air lowers the depressurization point at which spillage occurs, and I'm ready to change my mind.

Building depressurization is measured relative to a reference point, namely outside pressure. When you bring the firebox to outside pressure you haven't changed anything. The same pressure differential still exists between the room and the firebox.

The fix is to lower that pressure differential to 5pa with an engineered makeup air supply to handle whatever combination of exhaust appliances and building envelope leaks you have.

Norbert

--------------message separator-------------------------

To: "Norbert Senf" mheat@mha-net.org
From: Chris "Smith"

Subject: RE Fw Your Masonry Heater manufacturers...

Norbert,

You're certainly a stubborn man, as I am.

Since you are a mfgr and you want to dicuss this...lets discuss your study And I have to say the air flow difference between overfire and underfire is intruiging, especially your underfire unit with less flow than other overfires.

You say...

"Masonry heaters with overfire combustion air systems appear capable of operating with maximum air consumption rates of 30 L/s or under.

The underfire air units tested required considerably more air. In a typical R-2000 house, drawing 30 L/s of inside air would result in only about 3 Pascals (Pa) of depressurization, well within any house depressurization limits."

So a 2 Pa (0.008" WC) difference (3-5) is ok for you, if your grand daughter was in that room and turned on the adjacent bathroom fan while your daughter was cooking nearby on the stove with the kitchen hood blowing away? Yes your heater meets room depressurization limits currently established...what about all those other homes we'll never see with the most screwed up air system on the planet?

You say...

"One problem with some wood heating devices is that the chimney flow may reverse when the fire dies down, causing smoke and/or carbon monoxide spillage into the room. Testing showed that this is not an issue with masonry heaters, as the basic design stores large amounts of heat that maintain chimney draft even after the fire subsides.

The data supports the view that the majority of masonry heater types can be expected to function properly in airtight houses, with or without outside combustion air supplies."

So why not put them in for saftey? Remember your grand daughter!

And you say...

"Backflow prevention dampers may provide a solution to the reverse flow problem"

So why not put them in for saftey? Remember your grand daughter!

----------------------------------------------

To: Chris "Smith"
From: Norbert Senf
Cc: John Gulland

Subject: RE Fw Your Masonry Heater manufacturers...

At 0507 PM 2001-08-29 -0400, you wrote

(snip)

You say...

"Masonry heaters with overfire combustion air systems appear capable of operating with maximum air consumption rates of 30 L/s or under.

The underfire air units tested required considerably more air. In a typical R-2000 house, drawing 30 L/s of inside air would>result in only about 3 Pascals (Pa) of depressurization, well within any house depressurization limits."

If the -3 pa depressurization is unacceptable (remember, this was for the tightest house ever tested, with an ELA of 22 sq.in.), by all means introduce some makeup air. In reality, these houses all have HRV's. The two 5" HRV holes in the house envelope are taped up during the blower door test. Real world depressurization from a 30 L/s exhaust flow would be much lower.

So a 2 Pa (0.008" WC) difference (3-5) is ok for you, if your grand daughter was in that room and turned on the adjacent bathroom fan while your daughter was cooking nearby on the stove with the kitchen hood blowing away? Yes your heater meets room depressurization limits currently established...what about all those other homes we'll never see with the most screwed up air system on the planet?

Canada has an airtight housing standard, R-2000. It includes a house depressurization limit (HDL), namely -5pa. It also includes a depressurization test if you have naturally vented combustion appliances - you turn on the largest 3 exhaust appliances simultaneously and measure the house pressure. If it is less than the HDL, you supply powered makeup air, electrically interlocked to the exhaust appliances.

Masonry heaters are remarkably tolerant to house depressurization, by the way, because there is a lot of stored energy to power the flue for a long time, if necessary. As you may be aware, Minnesota has recently passed a very strict residential ventilation standard. My study was used to qualify masonry heaters in Minnesota for an HDL of -15pa.

If you have "the most screwed up air system on the planet" in your house, outside combustion air isn't going to save you. That's my point.

If you are actually interested in the engineering background on this, you should familiarize yourself with the groundbreaking work that was done by the Research Division of CMHC in the 70's and 80's on these matters. They tried several different schemes with outside combustion air supplies. Jim White was their chief scientist and is an extremely bright guy. The Canadian Housing Information Centre at (613)748-2312 can give you a very long list of publications on IAQ. Because the work wasn't done in the U.S., you guys are now in the process of reinventing the wheel on this.

You say...

"One problem with some wood heating devices is that the chimney flow may reverse when the fire dies down, causing smoke and/or carbon monoxide spillage into the room. Testing showed that this is not an issue with masonry heaters, as the basic design stores large amounts of heat that maintain chimney draft even after the fire subsides.

The data supports the view that the majority of masonry heater types can be expected to function properly in airtight houses, with or without outside combustion air supplies."

So why not put them in for saftey? Remember your grand daughter!

My point, once again, is that you are fooling yourself if you think an outside air supply increases safety. If your house has a pressure problem, find out why and fix it. Why would anyone find it acceptable to live in a house with a pressure problem and have to kludge a fix to their stove or furnace?

The best reference on doing the "house as a system" diagnostics is John Gulland's book. As a matter of fact, he teaches seminars on it to the hearth industry and to chimney service professionals. These guys are out in the field and see lots of problem houses every day. He just released a video on doing a house pressure test - this stuff is starting to get pretty mainstream in the hearth industry. More and more service people with micromanometers in their tool box.

One of the studies CMHC did was a survey of the existing Canadian housing stock. They took a sample of 500 houses from coast to coast, and all age groups. A very high percentage of them, something around 50%, I believe, had low level CO problems. Most of it was from furnaces with exterior chimneys and barometric dampers spilling exhaust gases into the basement during startup. This is aggravated by the negative pressure in the basement caused by the stack effect in the house. Add a Jenaire and you're really asking for trouble.

Our operating instructions advise our clients to install a CO monitor with a low level readout (Nighthawk makes a good one that sells for about $30 at Home Depot), and I believe our National Building Code requires this for all new houses with naturally vented combustion appliances.

On a masonry heater, draft is lowest at startup. If you get spillage, you know about it because you smell wood smoke, unlike your gas furnace in the basement. You'd choke from smoke before you ever got a CO dose. During the CO (charcoal) phase of the burn, unlike a metal wood stove, the chimney draft on a masonry heater is high, way higher than your gas furnace. If the room is depressurized, the chimney draft is countering that by keeping the firebox at a lower pressure than the room. Now, if you connect that firebox to a higher pressure, namely zero (outside), you aren't doing anybody any favors. If you then put a fan in the air supply and bring the firebox pressure positive, that's when you are more likely to kill somebody, particularly if they have a bad firebox door gasket.

What I think is really unconscionable is a company like Jenaire selling indoor grills with high powered exhaust fans and neglecting to include a powered makeup air supply. These things causes more depressurization problems than anything else I've seen - this is what your grand daughter should be worried about.

And you say...

"Backflow prevention dampers may provide a solution to the >reverse flow problem"

So why not put them in for saftey? Remember your grand daughter!

Check out the CMHC literature on this, and we'll talk.

......... Norbert

---------message separator-------------------------

To: "Norbert Senf" <mheat@mha-net.org>

Subject: How about a shortcut or link to that page?

>Check out the CMHC literature on this, and we'll talk.

-------message separator----------------------------

To: Chris "Smith"
From: Norbert Senf

Subject: RE Swedish masonry heaters..

At 0516 PM 2001-08-29 -0400, you wrote

Norbert

Check out this Swedish unit. It uses a combustion air fan.

Why don't you use a fan?

Chris:

I know you HVAC guys love your fans, ducts, and pumps. Masonry heaters work very well without them. I had a lot of happy clients during the big ice storm here a few years back when the power was out for 10 days and a lot of people were living in shelters.

I've been at it for twenty years, and am ready to make improvements at any time. If a combustion air fan is an improvement, as you claim, is it too much to ask for some data, any data, to show a benefit??

Excuse me for being a big sceptical, since everybody seems to be a fireplace expert.

Norbert

------------message separator---------------------------

To: "Norbert Senf" mheat@mha-net.org
From: Chris "Smith"
Subject: RE Swedish masonry heaters..

No, I also believe in the KISS principle!

But I want to understand your basis for or not doing it.

I do like your system and I like your simplicity.

Why not put a finish texture on the exterior of your modular blocks, molded into the shape of stones, bricks, tiles, or stucco? Your customers would save on setup costs, and it would be a faster install!

Chris "Smith"

-------message separator--------------------------------

To: Chris "Smith"
From: Norbert Senf

Hello Chris

Our system is a masonry heater core, which requires a separate facing. We've considered doing some modular facings, but being small we have to be pretty careful to pick and choose what we put development effort into. Tooling up for anything, as you know, is expensive.

There is a slip joint required between the core and the facing so that the core can slide up and down slightly inside. If it were one continous casting you would get horizontal thermal stress cracks on the outside.

A main difference between the systems we build here and the European systems such as the Cronspisen is that North American systems are larger, designed to heat houses, whereas European systems are traditionally room heaters. It is a fairly stressful thing to put 60 lbs of wood in a firebox, go from a cold start to full tilt and back, and be able to survive several thousand cycles. With smaller capacity heaters such as the Cronspisen there are a lot of problems you simply don't have to worry about because the thermal stresses are lower. One of the reasons we don't use underfire air anymore, aside from reducing emissions and excess air, is to lower the burn rate somewhat and reduce stresses.

We've already reduced installation labor and costs by going from a custom handbuilt core to a modular core. Modular facings would be nice to reduce costs even further. However, a heater has a fairly tough job to do, so there are certain things that you just can't cut corners on, or you will be guaranteed to have a callback, often a very expensive one. There have been a few people come and go over the years who thought they could make some money by lowballing things, and have lived to regret it.

Norbert

You are correct about us reinventing the wheel. We are seeing the dumb and dumber emerging over the concern for too tight houses (these would be in the 0.30 to 0.50 ACH natural range, incidentally). Most don't test, most don't know about air flow, most are happy to put a hole in the wall and move on, and few want to understand.

I have been advocating depressurization testing for a long time. It's part of our HWAP standards but foreign to our HVAC and Code communities.

Good luck. I never thought of you as a stove salesman. Am I missing something??

Thanks,

Paul Rimelspach