Heat two buildings with one boiler?

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New Member
Oct 2, 2019
Pequot Lakes, MN
I am looking at buying a used Hardy H4 owb. I would like to heat both my house and dettached garage with it, totalling about 3200 square feet. I am planning on running 1" pex to the house, for the garage I plan on using a 60k btu hanging heat exchanger. For the garage could I get away with 3/4" pex? And can I use a T off the pump on the boiler or should I use separate pumps? Thanks!
I would need to know distances in piping on the two loops but normally I'd use two pumps, flow rates stay higher with cheap smaller pumps. Garage may heat ok with 3/4” lines if it's a short distance.
Not sure how accurate an answer could be without knowing some heat loss numbers. And piping lengths. 'Get away with' is a pretty wide open term. 3/4" isn't really very capable. Even 1" may be quite limited when it comes to keeping a house warm in Minnesota.

Also anything underground needs to be good stuff. I.e., not cheap. Have you priced Thermopex or Logstor or the like?
I haven't decided if I'm going to use the foam in trench method or thermopex. The run to the house will be 65 feet, run to the garage about 75 feet. Also, is it worth the extra money to use pex-a and expansion fittings? I've been reading that with expansion fittings there is less restriction due to slightly larger internal diameter.
The losses incurred by using poor insulation on the tubing will be many orders of magnitude higher than any restriction due to the fittings.

A slight reduction in flow rate is just lowering the amount of heat the system can transfer from the boiler to the house. As long as the heat flow is still enough to support the demand from the house, it doesn't really matter. Tubing that is poorly insulated actively steals heat from the entire system which both lowers the amount of heat transferred to the house _and_ increases wood consumption, even when the house isn't calling for heat.
Just doing some math here, 3/4 is barely big enough to supply a 60,000 BTU heater at that distance. I'd do 1".