Using wood for home with large heat load?

[98kx1927]

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

 

[PassionForFire&Water]

unusual for TX probably.

I would say any gassifier, 30kW or 40 kW output, with 1000 gallons of thermal storage will do the trick.

And, most important, use firewood that is between 18% and 20% on moisture content

 

[Tennman]

Dave, Our BioMass 60 is rated per the manufacturer at 205kbtu/hr. I assumed an 80% efficiency on the advertised output or ~170K actual max output for system sizing. At 32-35F outside it idles.... maybe 50% of the time. When the temps are in the teens, very little to no idling meaning the house and the boiler system are absorbing about all that 170k. And when it hits 0F like last week (record low for us) I might run propane and wood to break even. I think you'll find your energy need isn't that unusual here.

 

[98kx1927]

Say we are looking at the BioMass 60. How much wood can be put into the firebox to provide 170k before running before reloading? Do you find you burn a load once, twice per day? I guess that is my biggest question.

I looked into sizing storage to provide heat for 12hours on a design day, but that is just too much storage. I guess the other thing to consider is that you aren't typically running at design load so the 1000 gallons will make a big difference.

 

[Boil&Toil]

I guess the other thing to consider is that you aren't typically running at design load so the 1000 gallons will make a big difference.

I'd bet the building work's Garn is in has a larger design load; so part of the equation is if the load is big, make the supply big, too. Of course, that building also has a monstrous oil burner for when the Garn's storage is exhausted, if nobody comes in to feed it. Or use two smaller boilers - if you have a 30KW and a 60KW then you can fire 30, 60 or 90 as the need calls for, but it is more expense - however it's also more redundancy if something breaks. It could also be a reason to consider (since you appear to be in the "options are still open" stage) if something a bit more automation friendly makes more sense for your use - a chip or pellet boiler rather than a stick-wood, for instance, or one "automated" and one stickwood.

Design load is an extreme that it's unusual to hit for more than a week or so out of the year (at least in these parts, and not every year at that.) If you have backup heat (oil, gas, etc) it's not the end of the world if it comes on and helps for part of that week, if you don't keep up with stoking. The storage is really most helpful at "regular" and "light" loads - allowing you to run a full hot, clean burn and store the output for use as you need it. If you don't have oil/gas backup, you might want another wood boiler (could be a cheap used non-gasifier) you can throw in the mix for that week, and you won't want to be away on a tropical island vacation then...or you can possibly even live with the pain of electric backup, so long as that doesn't go out.

 

[PassionForFire&Water]

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

How did you end up with 98 kBTU/hr?

What do you currently use to heat? oil? propane? ...?

And how much did you use? Gallons?

With the heating degree days for your area you can easily determine the max heat you will need

 

[hobbyheater]

Our design load was calculated (in 1981) to be 45,000 BTU's per hour . That figure has only be attained once for 10 days and that was back in Nov.1985 . The old Jetstream at 120,000 BTU'S per hour with 1,000 imp . gallons of storage only had to fire for 12 hours in each of those days .

 

[98kx1927]

The 98kBTU/hr came from the heat loss calculation after a ton of insulation work. It dropped by about 33% with the enclosure work.

As for backup heat, I'm still getting bids. One is to use the radiators in the home and covert from oil to a mod/con propane boiler. The second is to convert the entire system to a GSHP, getting rid of radiators and installing duct work. For the boiler option we will also be installing AC, don't know if it will be duct work, or mini-split systems. That is still being discussed.

I'm interested in a stick burner because I can get all the wood I want at no cost, just have to cut-n-split it.

Either way I will have backup heat, and it will be compatible with a wood boiler.

 

[Tennman]

We're at a latitude where our mean winter temp is ~37F. Passion above is asking good questions to help you get a handle on the real demand for the majority of your heating season. Last Monday our ~170kbtu boiler was inadequate for a once in 100 year event. Others will chime in to help you size the boiler for 95% of your weather not the once in a century day. There are many variables as to how often we load with outside temp being the biggest. Night time temps here are back to the low 30's. I loaded last nite at ~9:30 with the boiler temp at the setpoint of ~190. At 6AM the house was still warm from ~160F water and coals about gone. I loaded pretty full, not to the max, but full. It appears on average the EKO, BioMass, Attack and most of the other gassers seem to operate at nearly the same efficiency. So advice from an EKO 60 owner is as reliable as from a BioMass 60 owner. Unless you're way up on the TX panhandle your winter mean temp has to be less than ours. Share some more info on your home and mean winter temp for your area. Southerons like us are pretty rare here. I still have hopes of getting my storage on-line this season... if I can find some help. Then I'll finally be able to see the 60's full potential. I was unsure if heating with wood would suit my wife and I so I purchased the BioMass since it offered very good value. Had I known back then that we'd really enjoy wood heating I probably would have moved upscale to a Froling, Vigas, etc, but have no regrets. For the price and based on my zero experience it turned out to be an excellent choice with many happy operators. Enjoy. You're at the right place for an education.

 

[Tennman]

BTW, propane forced air was our primary until we added the boiler. It's now is our secondary. You should get many recommendations of the comfort and efficiency of radiant heat vs forced air. I'm stuck with forced air so I'll let the radiant guys fill you in. But adding the water to air heat exchanger to our existing heat/AC ductwork was pretty easy. Most here prefer radiant and convert to radiant from forced air as the preferred approach.

 

[98kx1927]

The home is in VA, not here in TX. We plan to move there in a few years after the kids move out

Design temps are typically 15F, the 98k was calculated at 10F so that gives a little head room.

The boiler on the top of my list is this one
(broken link removed to http://varmebaronen.com/vedolux-40-ub/)

or maybe the 50 if it needs to be a bit bigger.

How do you like the indoor aspect of it. Is it easier to haul the wood inside? Not sure if I like that or would prefer an outdoor boiler. Thoughts?

thanks
dave

 

[PassionForFire&Water]

You write: " I'm having a home ... ."
So, is this an existing home or a new build?
I assume if you have it, you know what it cost you to heat it and how many gallons you use to do it.
With this gallons of propane and the location heating degree days you can perfectly calculate your heat demand and this per month.

 

[98kx1927]

I just purchased the home from the bank. So I don't have any data on history. The home was built in 1927, is a solid brick two story home. Sorry for the confusion.

I had a home heating renovation company come out and do a blower door test, looked the property over and that is where the home envelope upgrades are coming from.

dave

 

[Floydian]

Hello Dave and welcome!

Where about in VA is the house located? That is a hefty heat load so I'm thinking the house is in the mountains? If so the cooling load might be fairly small unless the house has a lot of unwanted summertime solar gain on the south and west side or the attic is really short on insulation. For us there are usually a handful of days when AC would be nice but the nights are always nice and cool where we are.

Do you know the cooling load? Mini splits could be a good option for AC and provide backup and supplemental heat to a gasser and storage along with radiators. Decent units are going to way outperform any propane option too.

I gave some serious consideration to the Vedolux UB 40 but ended up with the 37. Very happy and Dean at (broken link removed) is great. If you go the natural draft route I think it's worth locating the boiler as close to storage as possible. Hopefully you can set it up with the top of your storage being above the top of the boiler, along with large diameter pipe and careful layout and you would have the ability to utilize thermosiphoning to storage as part or all of your overheat protection. I am a big fan of this approach for any wood boiler next to storage but especially see the value with a boiler that keeps on firing even when power is cut to the pump. This approach is not used much in the US but is very common in Europe from what I have read. Also, loading units are designed to work well with this set up as well.

I would definitely keep the radiators if you do go with a gasser and storage. They are cast iron, right?

Noah

 

[Tennman]

I drive thru the Shenandoah Valley often heading to Central PA or DC and admire many old brick farm houses. Over the years there have been many long posts discussing pros and cons of indoors vs placing the boiler in a outbuilding. Both sides are passionate and correct depending on your priorities. Indoor more efficient and convenient, outdoor keeps only hot water entering the dwelling. Many do not want to wade thru snow to service the boiler and keep boiler waste heat in the house. I love the worry-free freedom of being sloppy in the boiler barn with chips, splits, ash, and smoke and accept that I waste some wood. The indoor guys would never take theirs out of the house, the outbuilding guys would never put our "indoor" wood boiler in their home. Like I said, both sides are right depending on your priorities. You can PM me about the BioMass to discuss.

 

[98kx1927]

I've a building right out back of the house. I think that it was originally the well house. It still has a 1000 gallon water tank in it. Attached to this building is another building made to hold firewood. I suspect I could get about 2 cords of wood stacked inside it. I'm considering using this building to house the boiler as it will most likely double as my hobby shop.

I just don't see my wife, or myself for that matter, carrying the firewood through the man door, down the narrow staircase to the basement to feed the furnace. I guess I could make a way to dump the wood in through the basement wall, like a coal shoot or something, but am not sure it would be worth it.

dave

 

[jebatty]

These high heat loads blow me away. Our house is heated with 35,000 btuh at -30F, which means around 15,000 btuh most of the winter.

 

[dogwood]

Dave, I live in SW Virginia, a little north of Roanoke in a decently insulated 3000 sq ft home. A few years back I ran a few heat loss calculations using different, mostly on-line available programs after my first heat loss calculation yielded an anomalous result. The subsequent results averaged at least 20,000 btus less than your 98000 btus. How big a home did you purchase? Where are you located in VA?. Is the home further north or at elevation? Did someone provide you that heat loss calculation or did you do your own? I wonder what program was used? That result does seem high, especially if you've had the home retrofitted with insulation.Virginia has a fairly mild climate so you might want to double check that result with another program before you make the big investment in a heating system. Slantfin used to have a good program that others on this site frequently recommended.

 

[Floydian]

These high heat loads blow me away. Our house is heated with 35,000 btuh at -30F, which means around 15,000 btuh most of the winter.

I agree Jim. If I had the high heat load that Dave here has I would be making some major energy retrofit plans. I'd aim for getting that heat load down to the point that a couple of mini splits and a wood stove would easily take care of things.

Noah

 

[98kx1927]

The home is a solid brick home, 3300sf, built in 1927. I'm working with a company out of Roanoke that specializes in retrofitting old brick homes. Being solid brick there are a lot of issues when trying to insulate the home, if you don't want to destroy the home in the process. I've a plan to spray the crawlspace, and attic with foam and other upgrades. Unfortunately, there isn't really anything that can be done with the walls without entirely gutting the house, which I'm not willing to do.

The heat loss prior to the retrofits is around 150kbtu/h and had a 225kbtu/h boiler in it. Reducing the heat loss from 150 to 98 was pretty good. This is also why I'm very interested in using wood to heat the home. I don't know what program they use.

It is about an hour NW of Roanoke outside Lexington.

Hopefully that answers most of the questions.

dave

 

[Ashful]

These high heat loads blow me away. Our house is heated with 35,000 btuh at -30F, which means around 15,000 btuh most of the winter.

A difference in perspective, I suppose. I was wondering why the OP's making a big deal about just 98 kBTU/h. Seems fairly low.

 

[Tennman]

I just gotta ask. By "solid brick" do you mean like the old factories from the 1800's, a brick wall about a foot thick up to the eves, no studs, just maybe something to attach the wallpaper or exposed brick on the inside?

 

[98kx1927]

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. 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.

dave

 

[Boil&Toil]

A difference in perspective, I suppose. I was wondering why the OP's making a big deal about just 98 kBTU/h. Seems fairly low.

Depends on the construction, of course. My recent ~2000 square foot shop building specs out to ~30KBTU/Hr at -20F design - could be better but I hate dark holes, so I'm wasting heat on having windows (192 sq ft), which are almost 6000 BTU/Hr of the design load. I'm particularly amused that the 10x10 overhead door is less heat loss (503) than the 3x7 man door(528), due to "what's commonly available" even though the man door is "insulated." The OHD is R17.5, the MD is R3.5...

In old construction, unless you want to butcher the building at a cost exceeding tearing it down and starting over, you spend a lot more heat on large areas of poor insulation you can't (practically) do much about. It's only when people head the same way in NEW construction that I think they are crazy. Well, that, and pouring a concrete slab without insulation and PEX, if there's the slimmest chance you or someone else might EVER want to heat the thing, even if you don't plan to right now.

 

[Tennman]

Cool. Probably a wealthy individual who built that structure in '27. Have fun. Old home require lots of love....