Radiant versus convective heat

[byQ]

I guess I'm doing a radiant heat experiment. My half built house has a large masonry heater which is mostly radiant. And I'm building the house with south facing inside mass walls (15'x8'x.5') to collect more radiant heat through windows. Finally, I think I'm going to use large ceramic or porcelain tiles on some of the walls instead of sheetrock. Another mass for the radiant heat to be absorbed into. This will be a lot of mass - like Fred Flintstone's house..


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[byQ]

Here's Tulikivi pushing radiant heat.

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[peakbagger]

Radiant heat is directional. It you can see the heat source you can get warm. If there is a object blocking the view, then the radiation has to heat the intermediate object until it starts radiating. Convective heat flow heats the air and line of sight is far less important. Down side with convective flow is heat rises and cold air drops, that can create cold drafts. Talk to any mechanic who has worked in a garage with radiant heat panels in the ceiling, Works great when they are standing up but not so good when under a vehicle. Once a area gets to thermal equilibrium it really doesn't make a big difference, but if you want to heat up quick hard to beat radiant.

 

[brenndatomu]

Talk to any mechanic who has worked in a garage with radiant heat panels in the ceiling, Works great when they are standing up but not so good when under a vehicle

Radiant floor heat is where its at for a shop...of course then you need to kick the feet sticking out from underneath the vehicle once in a while to make sure they are still awake under there

 

[peakbagger]

When I took Siegenthalers heating course last year he had an example of a system for a municipal garage with radiant heat under the floor for the vehicles. Definitely the place for radiant floor. It also helped that they had no floor coverings so temps in the loop could be kept low. Even with proper slab insulation its interesting to see the tubing layout, pretty wide spacing in the center of the floor with denser spacing on the edges and ultradense at the garage door.

A former employer had a large tall airplane hanger that they wanted to heat for the corporate jet. I looked into gas fired radiant panels but the propane use was outrageous. Once I gave them a price for the install and ongoing propane use, they lost interest. Would have been a good spot for radiant floor in just one area of the hangar. Slope it towards a drain and tug the plane over it until its dry.

 

[Marshy]

I absolutly agree All I was saying is that in most houses either type will be able to heat just fine if it is sized correctly.

Agreed Probably the most important fact!

Going out on a limb here but I don't believe "a BTU is a BTU". I have gravitated towards a radiant wood stove (PH) and radiant floor hydronic heat kept at 65. (Onyx with Trio Boiler).Here in Vermont on the coldest mornings I can walk around in my skivvies. (Black that image out). The air is not warm, but I am warm. I don't know what is happening BUT when I visit neighbors who have baseboard convection heat, I am COLD. Radiant is more comfortable, that's why we like the suns heat (even though it is bad for some of us - skin wise)

I guess I'll be the first to dive into this thread with a more analytical approach...

What you are describing is called thermal comfort. We are all humans, not just another object trying to reach thermal equilibrium. Our comfort level within our home is affected by several factors. Thermal comfort is an analytical approach to exploring why you can be comfortable when standing on a 67F floor and have an air temp of 60F. Radiation plays a significant roll in thermal comfort as our skin is the receptor to the heat. Thermal comfort was an area that I was interested in several years ago but never dove into very much. I quickly searched the web in an effort to provide some quality content about it and found this site. Please have a look as this. This is really the basis of this thread IMO.
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I guess I'm doing a radiant heat experiment. My half built house has a large masonry heater which is mostly radiant. And I'm building the house with south facing inside mass walls (15'x8'x.5') to collect more radiant heat through windows. Finally, I think I'm going to use large ceramic or porcelain tiles on some of the walls instead of sheetrock. Another mass for the radiant heat to be absorbed into. This will be a lot of mass - like Fred Flintstone's house..
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I hope your flues are large enough to accommodate an insulated liner. If I was building new I would insist the flue have an insulated liner. It just makes sense no days. Eventually the only byproducts allowed by the EPA from wood stoves are going to be water vapor lol.

 

[Highbeam]

Once a area gets to thermal equilibrium it really doesn't make a big difference, but if you want to heat up quick hard to beat radiant.

That radiant sure is hard to beat but as you said, only really awesome if you are in the line of sight.

 

[Highbeam]

Eventually the only byproducts allowed by the EPA from wood stoves are going to be water vapor lol.

Condensing wood stove with forced exhaust. Efficiencies well into the 90s. I don't think we are that far away. I already have trouble keeping my flue gasses above the condensation point.

 

[jatoxico]

Condensing wood stove with forced exhaust. Efficiencies well into the 90s. I don't think we are that far away. I already have trouble keeping my flue gasses above the condensation point.

Tricky with units that are working off natural draft. As gases cool shorter would be better but can't afford to give up the draft. Answer is forced draft like you said but an appliance like that would be getting away from most of what I like about wood stoves.

 

[Marshy]

Here's Tulikivi pushing radiant heat.

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My BIL has an engineered soap stone fireplace similar to this. He has an open floor plan too. The square footage of the living space you are trying to heat dictates the mass of the built fireplace and how much surface area it has. I believe burns one to two arm loads of wood a day.

 

[tpenny67]

Do modern EPA stoves ever radiate like an old box stove? It seems to me that with firebrick liners to increase the temperature of the fire, the sides and back of modern stove will always be cooler. The glass front is a different matter, wow do those things throw off radiant heat!

 

[Marshy]

Do modern EPA stoves ever radiate like an old box stove? It seems to me that with firebrick liners to increase the temperature of the fire, the sides and back of modern stove will always be cooler. The glass front is a different matter, wow do those things throw off radiant heat!

I'm of the opinion that the new stoves do not radiate the heat like the non-epa stoves for the reasons you just stated.

 

[byQ]

If older types of stoves have heavier steel/cast iron but no firebrick than newer stoves with firebrick would have more mass so would probably radiate more. This would be especially true if there were firebrick on the inner walls of the newer stove (they would grab energy and hold it). But if the older stove had heavier metal and firebrick it would be the better radiator.

 

[webby3650]

Do modern EPA stoves ever radiate like an old box stove? It seems to me that with firebrick liners to increase the temperature of the fire, the sides and back of modern stove will always be cooler. The glass front is a different matter, wow do those things throw off radiant heat!

My Isle Royale sure does. It'll run about the same temps on all sides as the top. Many new stoves have shielding so it can be used in a modern home, more importantly so insurance companies can trust it. Not very many people want a stove sitting 36" from the wall. If you took the shields off of most modern steel and iron stoves you'd be surprised by the radiant heat. By shielding it, it's not only safer but adds a level of convective heat. So you get the best of both worlds, and it can be very close to the wall.

 

[begreen]

Exactly, the big difference often shows up in clearances.

 

[tpenny67]

My insurance company wasn't too pleased with the 118, and with the VT stove changeout program it's about to be replaced with a Quadra Fire at a bargain price.

Comparing the 118 and the Liberty, the Liberty has thicker metal, firebrick, and a convection chamber. My wife and I were able to easily pick up and move the 118 with the top and baffle removed, so maybe 250 lbs tops with all parts installed? The Liberty weighs 500 lbs, 'nuf said.

 

[webby3650]

My insurance company wasn't too pleased with the 118, and with the VT stove changeout program it's about to be replaced with a Quadra Fire at a bargain price.

Comparing the 118 and the Liberty, the Liberty has thicker metal, firebrick, and a convection chamber. My wife and I were able to easily pick up and move the 118 with the top and baffle removed, so maybe 250 lbs tops with all parts installed? The Liberty weighs 500 lbs, 'nuf said.

That 118 is a monster heater, I wouldn't discredit it ,its a very capable and proven heater.

 

[Attaboy]

That 118 is a monster heater, I wouldn't discredit it ,its a very capable and proven heater.

That Jotul 118 Black Bear is one he!l of a heater for its small size, it has a puny very narrow but lengthy firebox, Jotul have been making that stove for 100 years probably even more. If I had the space I would really love to have that stove, it is the type of product you use for a lifetime, pass it down and eventually even the grand children get to own it.

 

[Woody Stover]

I guess I'm doing a radiant heat experiment. My half built house has a large masonry heater which is mostly radiant.

I hope your flues are large enough to accommodate an insulated liner.

I'll be he's never even considered that, but you can never be too safe.

 

[tpenny67]

Unfortunately this 118 came with the house and apparently was abused by a prior owner. The sides are all cracked, large sections of enamel are missing, and chunks of rust are falling off the bottom. It's not worth repairing and fixing the clearance issues it has. It does burn amazingly clean and hot for a non-EPA stove. Perhaps air leaking in through the cracks is providing a secondary burn?

 

[webby3650]

Unfortunately this 118 came with the house and apparently was abused by a prior owner. The sides are all cracked, large sections of enamel are missing, and chunks of rust are falling off the bottom. It's not worth repairing and fixing the clearance issues it has. It does burn amazingly clean and hot for a non-EPA stove. Perhaps air leaking in through the cracks is providing a secondary burn?

No, old Jotuls did very well. I clean several of them each season, they are all very clean.

 

[webby3650]

That Jotul 118 Black Bear is one he!l of a heater for its small size, it has a puny very narrow but lengthy firebox, Jotul have been making that stove for 100 years probably even more. If I had the space I would really love to have that stove, it is the type of product you use for a lifetime, pass it down and eventually even the grand children get to own it.

Now the Black Bear is a whole lot different than the old 118. The original 118 had a bigger firebox, since there's no tubes hanging down and its baffle was flat not tapered like the Black Bear.

 

[byQ]

I'll be he's never even considered that, but you can never be too safe.

The chimney is inside the house except for the part that will be through the cathedral ceiling. It's centered so there won't be much above the roof. I'm using 12"x12" clay liners stacked. I put refractory mortar (sariset) between the clay liners and a hi-temp silicone to fill in the outer crack. I left 1/2" gap and bricked up around the clay liners.

I don't need to fill this 1/2" gap with perlite insulation do I? Just insulation around the clay flue once it is through the roof?

 

[Marshy]

If older types of stoves have heavier steel/cast iron but no firebrick than newer stoves with firebrick would have more mass so would probably radiate more. This would be especially true if there were firebrick on the inner walls of the newer stove (they would grab energy and hold it). But if the older stove had heavier metal and firebrick it would be the better radiator.

Radiant heat transfer does not concern mass of an object unless you are trying to determine how long it will take for an object to change a certain amount of temperature. Surface temperature of an object and area of the object dictate how much heat will be radiated. You can assume a constant stoves surface temp for all intensive purposes if you are looking at a snap shot in time, say peak temperature in order to make a comparison between stoves. Anything between the heat source and the surface that will be radiating will act as an insulator.
My old Shenandoah had one row of fire brick around the bottom of the fire box. There was equal amounts of surface area above the brick which were not shielded in any way to the surrounding heating space. Its very conceivable the larger amounts of surface area combined with the hotter surface temps cause significantly more radiant heat transfer vs my King that has external shields on the side and internal steel shields/fire bricks.

The chimney is inside the house except for the part that will be through the cathedral ceiling. It's centered so there won't be much above the roof. I'm using 12"x12" clay liners stacked. I put refractory mortar (sariset) between the clay liners and a hi-temp silicone to fill in the outer crack. I left 1/2" gap and bricked up around the clay liners.

I don't need to fill this 1/2" gap with perlite insulation do I? Just insulation around the clay flue once it is through the roof?

12x12 is adequate size to put an insulated liner in if needed in the future (like if you ever wanted to hook a BK King for example, a 8" liner would be needed). Im no mason, not even close but everything I have read about the clay liners is there needs to be an air gap just like you describe. Personally, I'd leave it the way your are building it.
Like you mentioned, you are creating a radiant heat experiment. If it works you'll stay warm but if it doesn't then you might just generate a lot of creosote and hopefully stay warm.

 

[bholler]

12x12 is adequate size to put an insulated liner in if needed in the future (like if you ever wanted to hook a BK King for example, a 8" liner would be needed).

It is a masonry heater you are not going to be able to install anything else in it or through it. And you wont be able to put a liner in it because there would be no way to do the bottom connection. That is why I suggested using either a class a chimney or installing a stainless liner from the start. The way it is if those liners ever need replaced it will be very difficult to do