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[Heyjohnj]

Hello all! Thanks for letting me in!  I just purchased a P&M BL 2840, and this looks like the place to be!  I have a lot of questions.  I was wondering if there was a page somewhere or sticky thread that describes best practices for plumbing things up.  I'm not doing anything too complicated--DHW, radiant basement slab, and HX for upstairs forced air.  I am thinking I will do this off of one loop from the boiler?  I'm just not sure what all components I should have, and how to configure them.  Any advice greatly appreciated!

[mlappin]

Generally your going come from the boiler to your domestic hot water first, then from there to your furnace HX. You can use either a flat plate which is quite common or a sidearm on your water heater. Most plumb the flat plate into the cold side of the water heater, then the warmed water flows into the water heater and it acts like storage, this way you can leave it turned on and if your gone several days the water heater will keep the water warm, or you can just unplug it and turn a tap on for five minutes to get hot water again.

Some parts of the country installing flushing ports to clean the flat plate is common while in other parts their is no need, all depends on your water quality. Here without flushing ports eventually a flat plate will clog up.

When hooking the heat exchangers up, for a flat plate you want your boiler water flowing the opposite direction as your domestic water. If your domestic enters the top and exits the bottom, then you want your boiler water to enter the bottom and exit the top. Same concept in the furnace, the air should be exposed to the hottest water as it leaves the heat exchanger. If the air is entering from the bottom, then your water from the flat plate or side arm should enter the port of the furnace exchanger that will have it flowing thru the top first and exiting the bottom.

Most every thing else can be found in the Plumbing section for a basic install.

[wreckit87]

I have a job to finish Tuesday with the same setup. BL 2840 with a Grundfos 26-99, loop inside through two 20 plate exchangers (DHW and radiant floor) and an 18x18 A/W exchanger in the plenum. As Marty mentioned, you want cross flow on all exchangers and hottest water in contact with the hottest air. Thermostatic mixing valves both on the DHW (120* to avoid scalding) and radiant floor (100-ish*) for optimal efficiency. Have done many others the same way including my own at home and everything has worked well. Almost everything can be bought from Menards or whatever store is nearby, the exchangers I usually get from Outdoor Furnace Supply on ebay, they've got great products and prices. Good luck!

[Heyjohnj]

Thanks for the info/advice! I think I am slowly getting on track. I have a few more questions. I am looking to get a Grundfos 26-99. It will be about 70 feet from the boiler to the house. It seems that 1 1/4" is the proper size pipe? Do I have to keep everything 1 1/4" on the inside on the main loop? My plate exchanger for DHW would have to have 1 1/4" ports, right? I plan to go through the plate exchanger, then I also will have a 14x18 HX for my upstairs, and a manifold feeding eight 1/2" loops in my basement. Loops are less than 300'. Thanks!

[braveblaster]

When hooking the heat exchangers up, for a flat plate you want your boiler water flowing the opposite direction as your domestic water. If your domestic enters the top and exits the bottom, then you want your boiler water to enter the bottom and exit the top. Same concept in the furnace, the air should be exposed to the hottest water as it leaves the heat exchanger. If the air is entering from the bottom, then your water from the flat plate or side arm should enter the port of the furnace exchanger that will have it flowing thru the top first and exiting the bottom.

Could  you please expand on theory/reason behind this?

No doubting nor question it just trying to expand my knowledge, thanks!

[wreckit87]

You want the most heat output possible from any type of exchanger right? Let's start with a flat plate- your incoming boiler water let's say is 180 degrees but your domestic input is only 55 degrees. If they're in parallel flow, your hottest boiler water is in contact with the coldest domestic water. The domestic will leech heat from the boiler water, so when it leaves the plate, your boiler water is only let's say 150. If the boiler water is only 150 on that end of the plate, your domestic simply cannot be any higher than 150. Now counterflowed, that 150 degree boiler water on the output of the plate is in contact with the 55 degree domestic. Are you with me still? Think of this a a preheat of sorts. Now as the domestic travels through the plate, it picks up more and more heat because the boiler input is still at 180. So once the domestic is exiting the plate, it's in contact with 180 degree boiler water, so if flows are correct, you can essentially have 180 degree domestic to fill your tank with.

Same goes for the air to water exchanger in the furnace plenum. That boiler water entering the top (updraft furnace) of the coil cools on its way down through the coil because the air is leeching that heat. But at the top, said air is already "preheated" and the last fin the air sees is in contact with 180 water again so if the stars align you could have 180 degree air instead of 150. Know what I mean?

[E Yoder]

You want the most heat output possible from any type of exchanger right? Let's start with a flat plate- your incoming boiler water let's say is 180 degrees but your domestic input is only 55 degrees. If they're in parallel flow, your hottest boiler water is in contact with the coldest domestic water. The domestic will leech heat from the boiler water, so when it leaves the plate, your boiler water is only let's say 150. If the boiler water is only 150 on that end of the plate, your domestic simply cannot be any higher than 150. Now counterflowed, that 150 degree boiler water on the output of the plate is in contact with the 55 degree domestic. Are you with me still? Think of this a a preheat of sorts. Now as the domestic travels through the plate, it picks up more and more heat because the boiler input is still at 180. So once the domestic is exiting the plate, it's in contact with 180 degree boiler water, so if flows are correct, you can essentially have 180 degree domestic to fill your tank with.

Same goes for the air to water exchanger in the furnace plenum. That boiler water entering the top (updraft furnace) of the coil cools on its way down through the coil because the air is leeching that heat. But at the top, said air is already "preheated" and the last fin the air sees is in contact with 180 water again so if the stars align you could have 180 degree air instead of 150. Know what I mean?