Seton stove said:
I'm having problems getting a large slab to heat up using a Seton 300...his biggest I believe?
Running 3/4" line Pex 150' in a 4" flex line that's uninsulated except for 2-4" of rigid over the top...all above groundwater.
At the manifold in the warehouse (uninsulated), I'm tapping into 7/500' 1/2" lines and seem to only be getting 2 to 2-1/2 gallons of flow total.
Temp is around 170 degrees leaving the heat exchanger near the stove and 130 at the end of the 150' run...the return is down around 100 degrees.
2 questions on the 3/4" supply/return lines...
Should I upsize to 1" or 1-1/4"?
Should I use insulated PEX (if I upsize), or spray foam (If I retrench)...(has anyone tried those small cans or containers of spray foam?...Is there a special density or ? when purchasing it?
Fred Seton has suggested I install a mixing valve between the heat exchanger and the pump going to the warehouse to keep the return temp up. Does this sound correct?
Regards, Scotty
PS...I'll be posting about my "MAJOR" creosote problems along with some pics that will have you smiling.
Let's start at the beginning. The first question you have to ask in any situation is what is the heat loss of the structure. From there you can determine flow rates required which will tell you tubing size, loop length, and circulator selection. From there you have to look at the type of equipment and heat emitter being used to select the right control set up.
Here's some rules of thumb: rough but generally accepted as safe
The following flow rates will all develop about 6' of head per 100' of the corresponding tubing size.
Using a 20* drop you can figure that each gpm is good for 10,000 BTU of heat transfer.
1/2" = 2 gpm
3/4" = 4 gpm
1" = 8 gpm
1-1/4"= 15 gpm
1-1/2" = 22gpm
2" = 45gpm
Note that the 6' of head is PER 100' of tubing length. Taco or Grundfos' website will have specs detailing the performance curve of the circ you're using.
Loop lengths recommended for good performance without resorting to ultra high head circs in a slab heating application (IE) 009/0011/26-99
1/2" 300'
5/8" 400'
3/4" 550'
Each of those will give you about 1-1.3gpm per loop or using the 20* drop, 10,000 - 13,000 btu per loop.
A well insulated cement slab in a building with normal heat loss will require no more than 120* water and usually it will be closer to 100-110*.
Now back to your system............
I'm assuming that your building is about 3,500 sq ft based on the 7-500' loops. 30 btu's / sq ft. (WAG) would equal about 105,000 btu heatloss. This translates to roughly 10-11 gpm flow required.
From that you can see your main loop out to the building should be 1-1/4". A 007 Taco or a 15-58 Grundfos will provide all the push you need to get the water there and back.
In the shop you have loops that are overly long so the temp drop is going to be higher than you would like due to reduced flow rates. In a warehouse application the excessive temp variation in the loop probably isn't a big deal other than you'll probably have to use a high head circ. (009)
Seeing as you have no storage you'll have to limit flow or temp drop in order to keep water temps up in the boiler above the creosote threshold. Then in the warehouse you could use a straight thermostatic mix vavle to limit the temp going out to the slab .
A cement slab can drain enormous amounts of heat whil coming up to heating temps. Far more than the actual heating load per hour would normally be. Picking up a load like that with no storage or backup means you have to rely totally on the output of the boiler. If the pickup load is greater than the boiler output you'll find that the boiler temp will just plummet and stay there. Hence the need for a mixing device in order to protect the boiler from condensing temps.
Tell us how you're system is piped exactly. What model circ do you have on the 3/4" lines and what model is running the warehouse floor?
Are you using a thermostatic mix valve to drop the temp going to the slab?