Extra Heat

Hello all,
I have been burning coal in my Harman P61 pellet stove for about a month and a half now and all seems well. I know I will not get the full BTU's from this stove because it was built to burn pellets and is rated at 61000 btus on a hi fire rate. I assume I am getting somewhere around 40000 btus based on the older 44 Magnum's design. I have built a W shaped hot water coil out of 1'' dia. sched 40 stainless tubing that is approx. 5 feet long. I also have 2 heat exchangers, 3 cores deep with 6 passes of 3/8 copper tube and aluminum fins approx 8''X10'' surface area on each one. I am planning to mount the coil vertically along the back of the stove in front of the fire brick to facilitate easier cleaning of the stove. I would like to mount either one or both of the ht exch. in the air handler of my heat pump/cent air system and use the fan on its lowest setting to supply warm air to the house. I know I will need to install an exp tank in the system, and plan on using ball valves to help regulate flow and a T&P relief valve for safety. I would like to use PEX for this install but have never used it before,and have read that the max temp for safe use is 200 deg F. Just thought I would run my plans by you all to see if I missed anything. This site is a wealth of info. and I thank you.
Bill

The Pex I've seen is rated 180 and 190*. Also, no Pex within 18" of the stove. I'm running undeground pex and discovered my boiler cn easily make 220* and a bit above. I installed a mixing valve to ensure the Pes never see's over 180. You sound quite inventive.... got pictures?

Make sure there's no way to shut valves and put the pressure relief valve out of the loop. Some people put two relief valves, one on the tank & one very near the coil in the stove.

All right,
No pics as of yet but another fly in the ointment. As I was picking up my circ. pump today the plumber asked what I was doing so I described my system to him. His biggest concern was my lack of volume of water. I am guessing less than 5 gallons total. He has suggested that I may want to get ahold of an old 30 gal. hot water tank to use as sort of a dump zone. Plumb the return from the heat exch. into the tank, then back into the coil in the stove. He even suggested going with a length of tube and fin baseboard, about 8 ft. should do it,also plumbed from the return of the heat exch. But still suggested a larger volume of water. Now I'm questioning my design. I thought that the less water to heat the better,but I realize this might not be the case for this homemader. The heat exchanger's (I have 2 exactly the same) were used in an aftercooler capacity,reducing air temps from 325* to 180* using "tower water" at approx 60* plumbed with 3/8" i.d. hose at about 30psi. Effectively air to water. So I thought my "delta T" would be O.K. using them as water to air, plumbed with 3/4" pipe at approx. 12psi. Am I wrong?
Bill

I'd think that as long as you can get rid of the BTUs as fast as they are made then you'd be OK with a low volume of water. You'll know real fast!

Problem is, if you suck the heat out of the water in the heat exchanger, it may not be able to recover fast enough which circulating thru the stove, that why he is talking volume, If you get a 20-30 degree drop, your stove may not be able to make that up in the short pipe in the stove, then you have slow it down to absorb the heat, kinda of a vicious circle.

that is why boilers have the 20-30 gallon capacity so it can regulate the heat better. it all depends on how fast your stove can heat it up and how much you need to put into your plenum and the BTU rating of the heat exchanger. A lot of factors, you would need to do a BTU calc to see what is going in and going out, based on flows, etc....