Looking for a wood boiler to heat my 11000 sq ft shop and 6000 sq ft home .... the basement and shop has pex in the floor already for Infloor and both levels of the house are currently forced air electric, and will have to have a heat exchanger added.
My direct experience with boilers that may fit your heated space needs includes:
1) A Froling FHG-L50 (170,000 btuh with 1600 gallon storage tank) heating a poorly insulated 6000 sq ft residential/visitor center, with two hot water to air plenum heat exchangers, also domestic hot water.
2) A Garn WHS 3200 (tested by me to provide 500,000 btuh continuous output for up to about 18 hours), 3200 gallon integrated storage, supplying hot water heat (with the Wood Gun) mostly through fan-coil units and domestic hot water for a 56000 sq ft residential/educational center.
3) A Wood Gun E500 (tested by me to provide 500,000 btuh continuous output), 4000 gallon external storage, supplying hot water heat (with the Garn) as indicated in (2).
4) The Garn and Wood Gun effectively share their storage capacity, resulting in 7200 gallons of available storage.
5) All boilers require well seasoned wood. Froling smaller splits, 4-6" plus some larger, 28-20" length. Garn and Wood Gun will accept smaller and larger splits, 24" length for ease of handling. Keep in mind that larger splits can take more than one spring-fall period to season.
Alll these boilers meet 100% of space heating and a very high % of domestic hot water heating needs through the coldest winter MN has to offer -- average January -10F to +5F would be the coldest month, with periods during the winter with temperatures plunging much lower, even into the -40'sF. Average wood consumption of about 100 full cords each winter, mixed hardwoods and pine.
For your needs the Froling by itself would work well to heat the house. It is both easy and a charm to operate. It requires storage, and I believe 1000 gallon is a reasonable minimum, the 1600 gallon is excellent to provide hours of heat between needed firings. With proper plumbing it will provide low temp for in-floor pex + higher temp for the water to air plenum heat exchanger.
I thing either the referenced Garn or the Wood Gun within my experience are too large for your needs. Smaller capacity models probably would work well for you. I have no information to suggest that smaller versions would operate any differently than the larger versions. Both are very good boilers. I would not recommend a Wood Gun without storage, although it is advertised to work without storage. Storage allows the Wood Gun to excel in performance by eliminating all idling and restart issues. The Garn has integrated storage.
The Garn is very easy to use, is intended for a batch burn operation, and excels in meeting needs for water temps of 140F and below, although it can meet needs for higher temp water. This is because the Garn can perform a batch burn to heat its integrated storage to a much higher temperature, then be allowed to burn out and reduce coals to ash, and to use the storage to meet heating needs until another batch burn is required. I don't get too concerned as to whether or not the Garn is a "true" gasification boiler because it is very efficient, probably qualifies as gasification, and is about as smoke free as a cordwood boiler can be. Based on quantify of ash/dead coals remaining after a batch burn (which need to be regularly removed), I don't believe the Garn is as efficient as the Wood Gun
The Wood Gun also is very easy to use and with adequate storage performs equally as well as the Garn, and would operate in a similar manner to the Garn, the exception being that the Wood Gun reduces the wood to fine ash as it burns, ash residue is collected in an ash barrel, and the Wood Gun can be operated continuously if needed. An advantage of the Wood Gun (or other gasification boiler with storage) over the Garn, if this is important, is that the Wood Gun can provide very hot water (160-185F) directly from the boiler even if the external storage is not first heated to this temperature, while the Garn generally must first heat its integrated storage to provide the very hot water. This is dependent on the amount of mixing that occurs in the Garn tank during the batch burn.
The amount of storage you have will dictate how long you will be able to provide needed heat between boiler burns. This is mostly about the math in calculating heat demand and stored btu's. Cordwood boilers need to be regularly fueled and if they cannot be tended during absences, a backup heat plan will be needed. In this regard, since it appears that you now have heating capacity installed, I would believe that your existing heating can be your backup and you shouldn't have to add another backup system.
If you want much more detailed test burn information on the Wood Gun E500 and the Garn WHS3200, send me a PM and I will provide you with the links to that information. Best of success on you biomass heating venture.
