Radiant floor heat questions

Csmith1967

I built a wood fired boiler from a 250 gallon LP tank. I put a 40 gallon burn chamber in it and the boiler (or water heater as it does not boil) holds about 180 gallons of water. I fired it up and got the water up to 170 degrees consistently, and hit 180 a couple of times. I plan on running it about 155-160 degrees.

I purchased 1250' of 1/2 pex and two manifold sets, and two circulating pumps. House floor plan is 24x40 with 2x10 joists in the basement. I am going to run the pex in between the joists. Basement is wide open, no walls.

First question is what is maximum length of 1/2 pex loop I want to deal with?

Second. Circulating pumps. Do I want them to push water through the pex or pull it?

Third. I bought 1" pex to run from boiler into house and then for return line. Manifolds are going in basement so I don't have to go out to boiler to adjust valves to turn a zone up or down. So pump is going on the 1" line. I have pipe insulation to go on the 1" pex line so heat loss is minimal. And the 1" lines will only be about 35-40' long and all inside house. Nothing is exposed to outside. Boiler is in well insulated shed on side deck. Question: Is using the 1" pex to and from boiler better than having four 1/2 lines to and from boiler room?

I am on the Iowa/Missouri border. Top of Zone 5 and bottom of zone 4. Thanks for your input.

Craig-

Ironman

You need a lot more things to make it work correctly.

For starters, have you done an accurate heat loss calculation to determine how much heat the structure needs?

Second, are you planning on using good quality extruded aluminum heat transfer plates? Without them, you won't transfer enough heat to the structure to properly heat it.

Third, you need to have the floor separated from the boiler by a properly sized heat exchanger so the house side can be pressurized. This will entail some ancillary components, too.

Tubing wise, 1/2" pex should be kept to 250' per loop or less in order to use standard circulators and keep electric usage low. You also need to use O2 barrier heating pex, not the common plumbing pex that you find at the big box store.

You'll also need a mixing device to keep the SWT to the floor at 120* or less.

Regarding your wood boiler: it needs to have proper controls for safety and operation as well as a sufficiently sized relief valve. It should also have some form of dump zone in case it overheats.

WARNING: you're creating a potential bomb when building your own boiler and proper safety precautions should be taken. Everything should be designed around WORST CASE SENARIO, not NORMAL operation.

Csmith1967

Calm down Bob. It doesn't build any pressure. It is a water heater, not a boiler. Everyone just seems to call these things boilers. It is not and cannot be a bomb. Worst case scenario is I have a fire from the wood burning part, just like the risk with any wood burner. But I have installed fire sprinklers above it so no worries there. I also have heat barrier and metal floor pan in front to catch sparks, if any.

Safety is always first with me. I don't do anything dumb.

I've got everything covered for the most part. My biggest issue is where to put the pumps. If I use them to pull from water tank and push into system then they are running 180 degree water, potentially. If I put them on back end of circuits then they will be pulling 180 degree water into circuits/loops which gives the water some cooling off before it hits pump. I know from life that heat isn't the best thing on stuff so I figure the cooler the pumps run the better and longer.

My pumps are Stiebel Eltron Nonsubmersible Circulation Pump. 1/25hp.

I guess I should explain it is an open system. Simply sucks hot water from tank and dumps it back in, easy peasy. Nothing pressurized other than the minimum amount of pressure of the water moving through the lines. I don't have any antifreeze or coolant in the system. Just plain water.

So push or pull for the pumps? Does 180 degree heat matter on the Stiebel Eltron?

hot_rod

Since the heater is unpressurized keep that pump as low as possible, the water level above it is the only pressure to help prevent pump cavitation.
I’d second the use of a heat exchanger between boiler and radiant

google a Idronics 10 for more Piping ideas

hot_rod

https://www.google.com/search?q=idronics+10&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari

Csmith1967

thanks Bob. I am reading that pdf now.

I've thought about the heat exchanger. I actually bought the copper tubing to build one myself to immerse in my tank. But then I have to worry about sealed system, pressure, etc.. Figured it was easier for me to use hi temp marine paint inside my boiler tank and just change my water if it gets dirty/rusty. Nothing exposed for it to get contaminated with.

I'm going to try it the way I have it and if it works for what I want then I'm good. I have a custom wood shop so plenty of wood to burn, for free

Any thoughts on the 1" supply lines versus 4 loops into house?

Csmith1967

Reading the pdf I will now refer to my heater as an "outdoor wood furnace" and not a boiler. No more confusion.

hot_rod

A safer description😜. There are some listed, pressurized outdoor wood boilers available, Homemade devices are usually best described as wood furnaces. For insurance reasons also

Voyager

http://s3.supplyhouse.com/manuals/1322593642270/68976_PROD_FILE.pdf

Zman

(1)-1" is better than (4)-1/2".
It would help if you posted a drawing an the pump curve for your circs.

Zman

How are you planning on controlling the wood furnace temperature? With wood, it is very easy to turn it into a boiler.

Csmith1967

Zman, the burn chamber, even if fully loaded, won't push enough heat to boil 180 gallons of water. I tried. Most I got was 181 degrees, and that was only for 3-4 minutes. Peaked out and dropped back to 170 within 15 minutes and stayed there for about five hours. I figure on loading the burn chamber in the morning and before bedtime. Two burns a day to heat house up. Still have electric furnace as backup. If it gets real cold, -20 or below then furnace might kick in. Or if we are gone furnace is set on 60 and will kick in when fire burns out and house cools off. The two pumps I have can be used with solar backup battery bank and inverter as well, so if we lose power in winter I still have house heat.

My wood furnace has an open top, so even if it did boil it would just release steam into my boiler shed. There is no way for it to build up any steam pressure.

Thanks for the link to the GPM flow chart.

GroundUp

No aquastat or temp controller, no automated damper or draft inducer, no mixing valve, no heat exchanger, no problem?

Your load is going to vary throughout the day with outdoor temp and sunshine, so your preliminary testing is best forgotten. Add an aquastat or Ranco type temp controller as well as a solenoid operated damper plate to shut down the draft between calls for heat, so it can regulate itself with varying heat loads. You say there is no way for contaminants to get in, yet later say the top is wide open. We call that an atmospheric system and you WILL get crap in it. Be sure to test and treat the water annually.

As for the circ location, with an atmospheric system you will want it as close to the boiler as possible and pushing toward the load. Every inch of pipe upstream of the circ adds friction that the circ needs to overcome with atmospheric pressure AKA gravity to avoid cavitation.

As for the piping question, max 250 ft loops of 1/2" and I would go with the 1" mains over home runs. Say you have 5 total loops of 250ft split over 2 zones (2 and 3 loops, perhaps), each pump can run on low speed. My thought would be to put one 3 way thermostatic mixing valve on the boiler supply line and build a small manifold on the outlet to split the flow between the 2 zone circs, as they need to pull through the mixer to work properly. Your floors will not appreciate much more than 120 degree water, depending how you install the tubing (plates or suspended).

Keep a close eye on your delta T with a full heat call and make absolutely sure the return to the boiler does not fall below 135 degrees. This may require you to set your boiler temp above 150 as you've mentioned. Lower than 135 will cause both thermal shock to the steel, due to poor mixing within the water jacket running low temp emitters, as well as flue condensation which will have you chasing leaks until you finally scrap it.

Csmith1967

Wide open means it is unsealed. It does have a lid over it so any "crap" will be minimal. Dust that may sneak in. It's wide open in the sense that it isn't sealed so as to build up pressure from steam/boiling. I built a ball valve drain on the bottom front so I can empty and flush the tank as needed. Water is $3.50/1000 gallons here so it costs me less than 75 cents to flush and fill.

I do appreciate the professional pointers here. I know a home built system isn't what most of you want to discuss, but I do appreciate your time. Thanks for the insights.

I will keep all of you posted on the progress.

Craig-