Help Me Size Boiler and Storage

[bryankloos]

Hey Guys,

As you may know from previous posts I'm seriously considering the addition of a wood boiler to help with heating. We just purchased the house this last summer and this is our first winter. I installed a PE Summit which has been heating the house fairly well (non-ideal layout, compensated with fans/vents) with the exception of the really cold days (below say 15F). That said, the PE leaves some rooms colder that I would like. We run the oil burner as backup during the cold snaps.

After much research I am interested in installing a wood gasification boiler with storage. I like the Froling with lamda control as I like technology with bells and whistles. I was leaning towards building pressurized storage out of 2 500 gal LP tanks but this is not absolute.

Before I plan anything further, I would like to ask for help sizing a system and make sure I am on the correct path.

I have not yet done any real heat loss calculations, as well, I am lost as to how to do so. What I can tell you are some specifics about the house:

3200 ft2 Colonial built in 1976
Oil fired hydronic with slant fin baseboard
5 heat zones (1x2nd floor, 2xfirst floor, 1 basement finished room, 1xDHW)
Decent exterior insulation
Older single pane windows
The previous owner burned about 1100 gallons of oil last year though I was told by my oil company to expect to burn more towards 1500 given the size of the house, ouch). Either the previous owner kept the heat very low or the insulation is decent?

What else can I do to help with the sizing...

Thanks for the help and experience. This is a great forum with great people!

Bryan

 

[Mojoe]

Did the house come with "storm"/combination windows to put over those single pane windows in the winter? If not, and maybe even so, I'd consider new windows as they are such a major heat loss and would be a major factor in figuring your heating requirements.

 

[bryankloos]

The house does have storm windows and to be honest, the windows are not too drafty. That said, I do plan on upgrading to replacement windows down the road...

 

[Mojoe]

bryan, I'm not an expert like many who are on here, I'm also in the planning stages of a DIY boiler set up. Your existing oil fired boiler has a BTU rating that will give you some ballpark info. I built my place and have always used wood exclusively so I don't have any hard numbers. I've been using wood furnaces [hot air] but I want to combine a centrally located wood boiler with solar hot water and a lot of storage to heat 3 buildings and do some snow melting, too, if there's any extra heat. Where are you planning on locating your boiler?

 

[bryankloos]

The boiler will sit next to the oil boiler which will serve as backup, both in the basement.
The current boiler puts out 140 MBH.

 

[maple1]

I already did, in post 5 of your other thread:

https://www.hearth.com/talk/threads/i-want-a-wood-boiler-now-what.122701/#post-1644715

 

[Fred61]

The house does have storm windows and to be honest, the windows are not too drafty. That said, I do plan on upgrading to replacement windows down the road...

Even with no infiltration (drafty) your single pane windows cause a huge heat load. Your heating input must be enough to overcome the higher radiation coming from the glass and secondly your window acts as a convector of cold air similar to a baseboard convector for heat only the flow is from the top down as opposed to from the bottom up with the heaters. The more layers of glass or other materials such as the polymer in Low e windows between the outside and the inside reduce the inside surface temperature of the glass and the difference is huge both on the heating side and on the comfort side.

If you don't replace the windows you should fashion some sort of moveable insulation that can be put in place at night or any time the window is not needed for light or gawking.

 

[bryankloos]

I already did, in post 5 of your other thread:

Thanks maple, I now recall seeing this.

Looks like the FHG L 40 would be the best option, as I doubt I would need the 170K MBH of the 50...?


We have insulated drapes over the windows which are closed at night. I know, a Band-Aid for a bullet wound. I hope to get the windows addressed not this summer but the next (2015).

 

[Mojoe]

Even though you plan on putting yours inside, some units do provide for using outside air for combustion. Combustion air is an often overlooked but major factor. All that air exiting your chimney/exhaust has to come from somewhere - inside, heated - and is replaced with outside, unheated. Without supplying your unit with outside, preferably preheated, combustion air, you will cause a lot of cold air to be drawn in as replacement. Just a thought.

 

[Bad Wolf]

Bryan, I have a similar set up. 3000 sq.ft colonial, with a room over the garage, 1986 construction, 2x6 walls, double pane windows (Andersons) hydronic heat. I used to burn right around 1100 gallons/yr.

I now have a TARM Excel 2000 rated at 102,500 BTU/hr wood, 120,000 BTU/hr oil. I have 4 heating zones and one zone for the hot tub. I have an unpressurized 1200 gallon tank for storage. I also have a coil in the tank for my DHW.

So far it has kept me toasty warm. Of course a couple of weeks ago when it was 8 below I had to keep it running 24/7 for a few days. Depending on the weather I usually fill it in the morning (runs for 4 hrs) and again at night. Actual burn time varies accornding to the temp. I try to get the tank up to 175 before I let the fire go out.

I have been burning around 7-8 cords/yrs but as I said thats my DHW in the summer too. In the last 6 years I've burned about 100 gallons of oil.

If you're ever up my way (Colchester) give me a shout and I'll show you my system.

 

[flyingcow]

Two thoughts. Won't help you size your boiler but,

1500 gals of oil will be equal about 10 cord of wood, hopefully less. Maybe as low as 8.5 cord. Rough estimate.

We've put shrink plastic on the inside of our windows. It helps. Take a little bit of time and use the hair dryer to tighten it, not really noticeable.

A semi wild guess on storage. 1000 gals plus. Actually, that was 3 thoughts.

 

[henfruit]

If you like the Froling, take a look at the Vigas. The same type operating systems for about 30% less cost.

 

[velvetfoot]

Does Vigas have the remote control thing, or whatever it is, working? Like doing stuff (monitoring) from a computer?

 

[henfruit]

It is in the works.

 

[bryankloos]

Guys,

What are the pros and cons of pressurized versus non-pressurized storage in this application?

 

[flyingcow]

My biggest reason for unpressurized was the tank. The tank was something i could put together in the basement. And also I knew the reputation of the tank manufacturer. I really liked his HX's that he sold. They perform very well. Seemed like a good fit.

Sorry, i can't give you pro's and con's. A bit over my head, but this application worked so i bought it.

 

[Coal Reaper]

There is some loss with regards to rate of heat tranfsfer through heat exchangers. Not to be confused with loss in overall efficiency. In your case if your boiler was pressurized (and it may not be) and your heat distribution side is pressurized then you would have anunpressurized vessel inbetween them, storage. Now you have two heat exchanges through three mediums. As you get closer to full charge it becomes harder to match the temperature from one fluid to the next. You may have 5-10* drop between exchangers/coils. Flow rate becomes very important.
Unpressurized storage can be erected in rooms where pressure vessels couldnt fit through a door. Depending on the lining material you may be limited in max temp.
Pressurized storage requires expensive expansion tanks. I have $1000 in expansion tanks for my 1000gallon storage.
Unpressurized tend to not be very high. Vertical pressurized allows great stratification

i feel like there should be more pros for unpressurized...

 

[bryankloos]

Thanks guys, this is all very clear.
Given my boiler and distribution is pressurized, it would then seem logical to keep the entire system pressurized.
That said, for 500 gallon LP tanks, I will need to remove a door to the jambs, but I did want to replace with something insulated regardless... Two birds with one stone.