Good Day

[heaterman]

The circulator is a Grundos three speed. On hi I think it's pushing 11 gallons a minute. I thought about trying a larger one, but have not yet. When I say the boiler is working hard, it runs for long periords. It does catch up, but mainly when the garage is not calling. The retailer thinks I need to remove the heat exchanger, pipe the boiler directly into the loop and run everything at atmospheric. The boiler does have 310 gallons of storeage, so this makes scense. The plumber says that this will void the warranty on my new, New York Thermals propane boiler.

I would heartily agree with your plumber. Leave the HX in place.

Your problem is that the slab is capable of dragging more heat out of the system than the CB is able to replace on a relatively sudden basis. I watched a 3500 sq ft slab drain the heat from a CB7260 so fast that the fire was just nicely ramping up before the boiler protection valve (Termovar) kicked in and started bypassing the slab. I believe that unit is rated at over twice the capacity of yours IIRC and it was over an hour before the water temp in the CB started to stabilize.

 

[Noggah]

I think this is accurate. I am guessing that the slab has about 25 gallons of water at about 55 degrees that it is dumping into the system when it calls for heat. It pulls the stove water down about 20 degrees, but it stills gases fine. It just takes quite a while for it to catch up. I think that if I had some hot water in reserve when the garage kicks in it would alleviate this problem because it would not be such a shock. The stove would still have to run longer to heat the storeage, but the system inside would not get pulled down all at once. Right now if its cold I have to turn down the garage down until the house is up to temp, then turn it back up.

 

[heaterman]

I think this is accurate. I am guessing that the slab has about 25 gallons of water at about 55 degrees that it is dumping into the system when it calls for heat. It pulls the stove water down about 20 degrees, but it stills gases fine. It just takes quite a while for it to catch up. I think that if I had some hot water in reserve when the garage kicks in it would alleviate this problem because it would not be such a shock. The stove would still have to run longer to heat the storage, but the system inside would not get pulled down all at once. Right now if its cold I have to turn down the garage down until the house is up to temp, then turn it back up.

Exactly. You have to fight mass with mass if you're going to do it head on.

 

[Noggah]

Thanks for your insight. I think I'm on the right path. Go Big or Go Home.

 

[SmokeEater]

Manufacturer rating is 250k btu/hr. The feed and return for the boiler is 1in pex inside 4in corrigated pipe filled with spray foam. This seems pretty efficient. I lose about 5-8 degrees between the stove and house, 75 feet of pipe. I think being able to charge the storeage when the garage isn't calling would even out the highs and lows

If you could pump at 4 GPM in the 1" (flow charts say that's about max for 1") then even with a 30 degree delta T you would only move about 110,000 btus per hour. Your 2400 can make double that, so if the 1" can't carry the heat your boiler is going to idle some (maybe a lot!).

 

[Noggah]

Thank you to everyone that has posted to this string. It has been very helpful and given me things to look at and hopefully build a better mouse trap. I appreciate the help.