Purchased a used wood boiler, wondering if my plan sounds logical

[Kevin50]

I recently purchased a used Homesteader V 92 from Winkler, Manitoba. With it, I am also getting a hanging hydronic garage heater. The house and garage it's coming from are quite a bit bigger than mine. It is rated for 300k btu/hr. My current heat system is a propane boiler that heats my 2500sqft house, and does DHW through a boilermate tank. It is a baseboard heat system. That boiler has an input of 140k btu/hr and heating capacity of 122k btu/hr. My garage is 768sqft.

I am planning to use a plate exchanger to tie into the propane boiler supply in the house so that the propane doesn't need to fire up. Should I be able to run in series from that straight to the garage heater, then back out to the wood boiler return? One person I talked to said I might want to split it once I get into the house and have a separate loop to the garage. If I did it all in series, my total loop will be about 300 feet. The boiler is about 65' from the house, so I will be using thermopex (1"OD), buried 4-5' down, then running regular pex in my crawl space for the part under the house.

Main questions:
1. Should my plate exchanger be 140k btu/hr, or should I bump it up just to be safe?
2. Can I run both in series or would it be best to split once I get into the house? I think I'll have more than enough heat capacity, so I thought in series was fine but the one guy I talked to has me second guessing.

I'm really new to this, and I'm sure you may need more information to make a reasonable recommendation. Please ask what else you need, and I'll do my best to provide it. Any advice I can get will be greatly appreciate.

Thanks a lot,

Kevin

 

[Woodman1]

Most OWB's are grossly over rated with their advertised btu rating. Rule of thumb would be 50%. You will struggle to move much more than 80k/hour through a 1" pex line without a delta t beyond 20. That was what I did with my old OWB. I never saw any condensation in it from a low return temp, but be aware the possibility and resulting boiler damage without return protection. Will it work? Probably, I think most standard OWB are set up as you described. Will it be right? Probably not. And yes, I would go with at least a 140,000 flat plate.

 

[Kevin50]

Most OWB's are grossly over rated with their advertised btu rating. Rule of thumb would be 50%. You will struggle to move much more than 80k/hour through a 1" pex line without a delta t beyond 20. That was what I did with my old OWB. I never saw any condensation in it from a low return temp, but be aware the possibility and resulting boiler damage without return protection. Will it work? Probably, I think most standard OWB are set up as you described. Will it be right? Probably not. And yes, I would go with at least a 140,000 flat plate.

Thanks for the quick feedback. In order to keep my return temp from dropping too much, what would you recommend? A higher capacity pump? Larger diameter pex? Or something completely different?

 

[maple1]

Most times, boiler return temp protection is done at the boiler - a short bypass loop that sends enough supply right back to the return to keep boiler return above 140 when mixed with load return. Can use a thermostatic valve or a separate bypass loop pump controlled by return temp.

You might have to post more info for more answers to your questions. A total layout of everything with distances between everything, for starters.

 

[Kevin50]

Most times, boiler return temp protection is done at the boiler - a short bypass loop that sends enough supply right back to the return to keep boiler return above 140 when mixed with load return. Can use a thermostatic valve or a separate bypass loop pump controlled by return temp.

You might have to post more info for more answers to your questions. A total layout of everything with distances between everything, for starters.

I tried to get some information posted sooner, but have been swamped with other stuff since I got out of work today, and now I'm running it if time for the day. I attached a quick sketch of the layout with approximate distances. The pex outside will be buried 4-5' and the wood boiler location is maybe 2' lower than the ground at the house foundation so there will be a slight rise. Once in the house, the pex with be level in the crate except going up through the floor to the boiler, then back down to the crawl and it to the garage where it will go up the the heater, then back out to the wood boiler return.

After drawing it out, it looks like I'm actually around 230 for total loop, but with elevation changes of a few feet I think it would be safe to say 250-275 still. I'd rather be conservative than cut it too close.

Outdoor wood boiler: B
Propane boiler: P
Garage heater: H

Thanks again, most of this is new to me, so I appreciate the feedback and patience with questions.

 

[E Yoder]

I'd do a primary loop catching the propane boiler, a secondary with its own pump using close tees to the garage heater. This would allow smaller cheaper pumps which are less than half the cost of the bigger ones.
Just my 2¢.

 

[Kevin50]

Based on my sketch above, where would I want the split to the secondary loop?

 

[E Yoder]

I would pump the main loop through the flat plate heating the propane boiler, then plumb in a tee-valve-tee on the return and pump a secondary loop to the garage from the tees.
The valve is to help purge the first time.