Boiler piping help

[Alysdad]

Ok so here is the problem, I have a free boiler given by friend it's a pennco 70kbtu my problem is I want to use it to run low temp radiant floor loops. I can't figure out what the best way to plumb this would be. I'VE looked at heat xchangers but can't meet the required gpm on radiant side. I've looked at a primary secondary loop but my load is low. I have 7 300' 1/2" pex loops. There is three thermostats which I've realized would be a mistake trying to achieve a min gpm. So far the only thing that seems would allow me to match the gpm on the boiler regardless of load would be a primary secondary with closely spaced tees or a injection pump with bypass. I have been reading for 2 weeks now trying to figure this out. What I have learned is low load low flow systems are tough to design.

 

[frodo]

run your calculations using 3/4 instead of 1/2'' see what that does for you

 

[Alysdad]

Changing to 3/4" would double the gpm at same delta t but I have 1/2"

 

[frodo]

see what using all 3/4 pipe from boiler to zones and 1/2 tubing for infloor will give you.

if it does not work out..return the 1/2'' and get 3/4

 

[Alysdad]

Well I bought a house that had the pex installed already they are 1/2" home runs I am think about just throwing a few baseboards I have laying around under the house to increase load and obviously efficiency and expense. Or switch the boiler out to something more on point with a low temp system requiring at very least 2.7 gpm and at max 5.4 gpm I'm only supplementing heat with this system there will also be mini split heat systems in nearly all the rooms the house was built in 1880 so I ought it with hopes to change it but after getting prices I figured I may as well use what's here. I lift homes and am not good with boiler plumbing, thanks for your input frodo

 

[Alysdad]

Well I may end up with just purchasing a new heat source. PROBABLY a hybrid tankless like the Rinnai rh180. Let me know what you think if u get a chance to see it, max btu load is 70k btu hr but I have other heat source as well

 

[frodo]

Well I may end up with just purchasing a new heat source. PROBABLY a hybrid tankless like the Rinnai rh180. Let me know what you think if u get a chance to see it, max btu load is 70k btu hr but I have other heat source as well

if you buy a new boiler, call manufacture tech department, give them your data, they will tell you which boiler is right for your system