Using wood for home with large heat load?

[henfruit]

The Vigas line of boilers have 5 sizes that run 85,000 btus up to 341,000 btus per hour.

 

[TCaldwell]

it sounds like you have the air infiltration under control with your foam plans, but wondering if the high mass brick walls once warm will require such a heat demand.

 

[Boil&Toil]

wondering if the high mass brick walls once warm will require such a heat demand.

Mass, when insulated from the exterior, is a wonderful thing (which is why there's rigid foam on the outside of my frostwall/stemwall), but uninsulated mass still bleeds heat like nobody's business. Might work out in a few places where the sun always shines and it gets hotter than the house in the daytime, but on the East coast it's just a lot of square feet of a lot of BTUs/Hr/SqFt/DegF - 12" of brick might be all of R2.4 (or 1.2, depending on the brick.) A building with a perfectly insulating basement, a perfectly insulating attic, no air exchange and walls of 12" brick that was 18 ft high, 20 feet wide and 30 feet long would need 51,000 BTU/Hr to stay at 68 when it's 0 outside - or 102,000 using the more pessimistic number for R-value. Let it be bigger, it needs more.

Now, if you're willing to turn your old brick house into a stucco house, you can do some pretty nice things by using foam under the stucco on top of the bricks - but that is changing the character of the house, and not everyone wants to go there. I don't from the "I'm sick of dealing with old houses" direction, so I build an over-insulated new one, and other folks don't because they don't want to destroy the character of the old house they like...

 

[Ashful]

Brick walls about 1ft thick up to the eaves, but it does have studs with lathe and plaster. The radiator pipes go from the crawlspace up the outside walls to the radiators on the second floor.

Mass, when insulated from the exterior, is a wonderful thing (which is why there's rigid foam on the outside of my frostwall/stemwall), but uninsulated mass still bleeds heat like nobody's business. Might work out in a few places where the sun always shines and it gets hotter than the house in the daytime, but on the East coast it's just a lot of square feet of a lot of BTUs/Hr/SqFt/DegF - 12" of brick might be all of R2.4 (or 1.2, depending on the brick.) A building with a perfectly insulating basement, a perfectly insulating attic, no air exchange and walls of 12" brick that was 18 ft high, 20 feet wide and 30 feet long would need 51,000 BTU/Hr to stay at 68 when it's 0 outside - or 102,000 using the more pessimistic number for R-value. Let it be bigger, it needs more.

A couple comments...

This construction is transitional, and not typical of old houses. Almost any masonry house built prior to WW1 would have front and rear walls 18" thick and gable walls 18" - 24" thick, depending on the existence and sizing of chimneys in the gable walls. This framed house inside a masonry shell is the transition from traditional masonry houses (no framed walls, excepting interior partition walls) and modern stick-built masonry-veneered construction. It's not something I'd typically worry about preserving when considering insulation, being just a facsimile of the real thing... but 100 years from now someone will be upset I said that.

Dealing with the thermal analysis of true masonry houses is something that always seems to get HVAC guys into a dispute. So many only know how to deal with R-value, while others will argue that this is not the proper handling of this type of construction. Rather, they suggest it should be treated as a thermal mass, with inertia, always pulling ambient closer to soil temperature. I can understand this theory, but have not studied this enough to really know the details.

All the wiring I can see has been updated from post and tube, but I've not been able to see everything yet. There still may be some post and tube wiring in the house and possibly in the walls.

You have a big advantage over the rest of us old house nuts, in that you actually HAVE wall cavities in which to feed wiring! Many of us are living in houses with plaster right on masonry for exterior walls, and planked interior partition walls. No wall cavities for feeding wiring! I still have the plaster on masonry for my exterior walls, but my planked walls were framed out with "new" plaster and lathe walls and ceilings sometime around 1800 - 1820. All of our wiring had to be installed in those interior partition walls, or run behind baseboards on the exterior masonry walls.

 

[dogwood]

Dave, sounds like you've purchased a beautiful vintage brick home. I worked for a number of years in Natural Bridge which is in the general vicinity of where you might be. I've often times driven by and admired the fine brick homes in the area. Excellent choice. I'm sure you'll like living here, and welcome to the area.

If there are stud walls in your new home have you considered having loose fill insulation blown into the stud cavities from inside the home? You wouldn't have to gut the house to do that, just patch the holes used to blow the insulation in through. The retrofit company could advise you I'm sure. Best of luck.

Mike

 

[Ashful]

If there are stud walls in your new home have you considered having loose fill insulation blown into the stud cavities from inside the home? You wouldn't have to gut the house to do that, just patch the holes used to blow the insulation in through. The retrofit company could advise you I'm sure. Best of luck.

... just be damn sure there's no live knob and tube in those wall cavities, first! This is apparently a major issue with blown-in cellulose in older houses.

My 1894 addition is framed, and a previous owner had polystyrene beads blown into the wall cavities. I'm not sure this was a good choice, as we seem to get very strong draft thru those walls, so you might want to read up a bit on that option and make your own choice, if it's recommended to you by an insulation contractor.

We plan on tearing the outside sheathing off that addition, raising the foundation another foot, new sills, new insulation (likely spray foam), new sheathing, new stucco. Too many projects... too little time to make them happen.

 

[heaterman]

The heat loss of 98,000 sounds about right for your square footage, type of construction and vintage of the home so I'd say you can probably "take that to the bank".
What you have to decide is if you want to meet 100% of that load with the wood boiler or if you can live with an 80 or 90% capacity. Bear in mind that the 98,000 will happen for about 1-2% of the winter and it may or may not be worth your $$ to hit those conditions.

One thing that I haven't seen any chatter about while skimming through this post is the type of radiators in the home. I'm assuming they're cast iron but is the current heating system steam or hot water? If it's steam you'll need to take a look at the piping layout and also the type of radiator. Some rads are built for steam only and will not work with a hot water system. A radiator that can be used for both will be "connected", section to section across the top. A steam only radiator will be joined only at the bottom of each section and these will not work for hot water circulation.

We installed a Garn for a guy that owned an old brick house built in 1873 near St Johns Michigan. It had two courses of red brick on the outside wall, then a gap of about 6", then another row of brick on the inside. Plaster and lathe was bonded directly to the inside of the exterior wall. It was interesting to notice when we cored a 5'' hole through the exterior wall, that apparently at the time of construction, they had filled it with straw and plant material to provide some semblance of insulation. Most of it had crumbled into dust over the years since it was built but you could clearly see what the intent was. We ran a fish tape up the interior cavity just to see how high it went and the tape stopped at about the level of the eave, so it was wide open all the way up.
If that is the case in your home, I would think that area could be blown full of cellulose pretty easy with minimal damage to the brick. The guy we put the Garn in for was going to attempt that but I never hear if he had it done or not.

 

[98kx1927]

Radiator, steam vs hot water, all very good questions.

Cast iron radiators, two pipe steam system that I'm having converted to hot water. This is why I have lots of BTU numbers, converting from steam to hot water isn't as simple as swapping out a boiler. I couldn't have done the change out without the housing envelope upgrades, there just wasn't enough EDR to support that. I was also lucky enough that the system hold pressure so no leaks in the piping or radiators.

Live knob and tube wiring in the outside walls at this time in an unknown, and one of the two reasons I'm not insulating the walls. I need to investigate that. The other reason is that there has been some research done that can show damage to the bricks if there is any water penetration to the bricks. Without wall insulation heat leaves the building keeping the brick dry and safe from freeze/thaw expansion. With wall insulation heat no longer leaves the building at a rate large enough to dry the bricks and you can now have your bricks come apart due to freeze/thaw. I need to be comfortable with both aspects prior to wall insulation.

Here is an interesting article about this:
http://www.greenbuildingadvisor.com/blogs/dept/musings/insulating-old-brick-buildings

 

[Floydian]

Dave, you are certainly doing your homework-I'd say the old house is in good hands.

Does the heat loss calculation have an estimated annual heat load? It would be nice to have a good idea of how much wood you will need. Getting a couple few years ahead to ensure dry wood can be a challenge, especially when you might need 8+ cords/yr.(I'm guessing here)

Do you have any idea at this point of what kind of supply temps you will need to deliver to the radiators? This could be a big factor in deciding how much storage you may want/need. In other words, if you need 160+ supply temps at avg temps and 180 at design temp then the benefits of large storage would be minimal and a buffer tank sized to minimize idling might make the most sense. Whereas if you can use 120 to 140 in avg temps you could reap the benefit of convenience that larger storage volumes can offer. Adding some radiators to be able to lower your supply temps could be a good investment, IMO but it could be a total PITA too. It all depends.

Any chance you can post a larger image of your avatar? Sure looks to have a lot of character.

Noah

 

[98kx1927]

Right now I'm not happy with the supply temps. At design temp I need 180F, I don't have the number for "typical" days, still need to get that. I am looking into adding more radiators, but initially I think I'm going to go through a season or two before taking up that project. This will give me "real" data to make a decision.

These high supply temps were what got me wanting to ask my question. If I wanted to run at design temp, and have enough storage for 12 hours, it is just not going to happen. So I was then wondering what if I just "idled", am I going to have to load the furnace 4-5 times per day? That could get old quickly, luckily design days don't happen often. I can see on boiler specs what max btu/h is, but how do you figure out how much total heat it will produce on one burn? I don't ever see any guidelines about this. A boiler that can produce 150kbtu/h isn't any good to me if a burn only lasts 2 hours.

 

[maple1]

Usually specs will have nominal output rating, and burn time. Multiply them and you get total burn output. More or less.

EDIT: But if it doesn't spec burn time, most are 4 hours or so.

Also, I would be shopping for used cast iron rads while you're planning. Hard to beat for nice heat output at lower supply temps, and you should be able to retrofit a few.

 

[SmokeEater]

I've been reading for a while, and have not been able to see anything similar to my situation.

I've a home that after insulation upgrades has a heat loss on design day of 98kbtu/h. Anyone out there using wood to heat a home with this large of a heat load?

thanks,
dave

Tarm Biomass has several boilers that would meet your requirements. One, for example is the P4 pellet boiler in sizes up to 100 kW or about 300,000 Btu/hr with an efficiency of over 90 %.

 

[Ashful]

Silly question, maybe... but are you dead set on a wood boiler? A more conventional boiler (oil, nat. gas) or furnace (propane, heat pump) paired with a wood stove (or two) has satisfied me, and my heat load is WAAAaaaayyyy beyond you requirements. This was not done purely for utility, but more with the thinking that, if I'm going to do all the work of felling, limbing, bucking, hauling, splitting, stacking, moving, and loading wood... I want to look at a pretty fire! No sense in hiding it in the basement, was my thinking.

 

[jebatty]

... but how do you figure out how much total heat it will produce on one burn?

You can get a stab at this by using 6050 btu/lb of seasoned (20%MC) wood. Find out, with your species mix of wood, the weight of wood one firebox load will hold, multiply lbs by 6050, and you have approximate total available btu's. Actual output to your heating load will be somewhat less because you also will lose heat from the boiler, plumbing and from the tank to the surrounding environment. Perhaps use 85-90% of available btu's as what you actually will get into your heated space.

 

[maple1]

Silly question, maybe... but are you dead set on a wood boiler? A more conventional boiler (oil, nat. gas) or furnace (propane, heat pump) paired with a wood stove (or two) has satisfied me, and my heat load is WAAAaaaayyyy beyond you requirements. This was not done purely for utility, but more with the thinking that, if I'm going to do all the work of felling, limbing, bucking, hauling, splitting, stacking, moving, and loading wood... I want to look at a pretty fire! No sense in hiding it in the basement, was my thinking.

I don't think I could bring myself to move from a hydronic central heating system, already in place, to a couple of space heaters, especially with a heat loss like has been discussed, no matter how many pretty flames I'd be missing. With a heat loss this big hydronics are your best friend.