H2O-Air Heat Exchanger Installation

My water-to-air heat exchanger arrived and I am getting ready to install it but I could use some advice. I removed the plenum from the furnace and the heat exchanger sits nicely on top of the furnace, I was going to use some 1/4" bolts to hold it in place but I was worried that a gasket or strips of insulation or silicone or something might be necessary to prevent squeaks or it possibly shifting. What is the normal procedure for installing these things? Also, do I hook the supply from the boiler to the top or the bottom pipe of the heat exchanger or does it not matter? Thanks for the help! The only problem I didn't anticipate is the pipes coming off the heat exchanger come very close to the cold air return duct. I can either drill holes in the cold air return and run the pipes straight through the duct or solder on 90 degree elbows and divert the pipes around the ducts. Diverting them means two more bends but I'm not sure it will hurt anything besides the slight extra expense of the pipe and fittings.

Can you scan a drawing or post pics? We really need this for posterity. I don't see a problem with the pipe through the return air duct. You should be able to get some sticky back foam (Refrigeration tape? check it's high temp limits, some are like a soft foil) at the hardware if you think it might squeek, I was thinking whistle myself. I doubt if it will matter much which way you plumb it, but normally the two flows are from the opposite directions with exchangers. Heat flows down cold flows up sort of thing. I would cruise the outdoor boiler websites, some of them have some very detailed info on this. My biggest concern is the temp switch at the top of the furnace and how it will get the heat from your coil to make everthing work well. You have plenty of time to sort things out, take your time.

I wouldn't worry about the piping, whatever works best or is easiest. Adding an extra 90* shouldn't make much difference since you have a short distance to the boiler and not many ells in the system.

As for the mounting of the exchanger, I'd use some self-stick foam seal to seal around the outside to prevent air getting around the exchanger [if this is possible]. As for squeeks etc, I really don't know. Hopefully a member or two who have done these installs can help.

Greg L

some pictures

I would plumb the hot water in at the top. You could maybe get some sweat street elbows and clear the cold air duct? It looks like you have about 6" of clearance from your furnace, the street turns from the lip of the fitting it is installed in and would only add about an 1 1/2" to whats there now. They might give you the clearance you need. I also would put in a set of ball shutoff valves as close to the exchanger as is convienient. That would reduce the amount of heat lost to the coal boiler if you run off your furnace for a while.

Nice pictures. While it's a little late now it would have been interesting to measure the furnace blower current before the install and compare it to the current after the heat exchanger install. A before/after measurement would give and indication on how much additional load is placed on the furnace blower by the increased air flow resistance of the coil. I wish I would have though of it earlier. Come to think of it three measurements would be useful. Open as it is now (no load), original install (duct load) and with heat coil (duct + coil load). Just thinking like an engineer, wanting data.

I thought about that, I have a clamp on inductive ammeter for my Fluke somewhere around here, if I can find it I'll do some testing.

The coil doesnt look secured, he probably could get two measurments right now easy. Remove the coil and run the blower and read the amp draw. Replace the coil and run it and read it again. At least you will know the change in load. The duct should not add much, but like you say the data is priceless.
I will take a guess that it won't add more than 5-10% of the draw he has presently (1/2 an amp at the most?). If it gets close to the motors max rating, I would step up to a little higher HP motor. They only run about $60-80 even for a 3/4 HP. I doubt it will be needed though.

e.alleg, what is the HP on your blower motor?

It says 3/4hp, it's direct drive so I scrapped my plans for a different size pulley system. There is a large capacitor also mounted next to the fan, it's about as big as an old style round ignition coil or a can of red-bull. The label on the furnace says "max pressure .50 WC", I'm hoping the coil doesn't trigger this sensor to shut anything down. I'm glad I took all the covers off, the fan was covered in dust and will get a good cleaning. If it can't handle it then It'll be a good upgrade to buy a 2 or 3 speed fan motor.

This has got to be one of the first water coil installs described on this forum. At lease to this level of detail. Another useful before/after measurement would be duct pressure. I suspect the extra resistance of the coil will reduce the duct pressure causing a reduced air flow especially at the distant ends of duct runs. A manometer measurement would be ideal, but even a subjective toilet paper ribbon as a flow indicator would be useful. I know all suggestions are a little late, but there's always next time.

That is a big motor, I doubt it will have any trouble.

Today I tested out the coil installation on the furnace/blower side. Compared to no coil (original configuration) the airflow out of the farthest duct is reduced by about 1/3 to 1/2 if I were to guess. The good news is the house is much quieter when the fan is running, before the air blasting out made considerable noise, now it just blows up pretty smooth. I ran the propane furnace and not the coal boiler, all the heated air had to flow through the cold coil filled with 50 degree water. The air coming out of the ducts was luke-warm as expected, as a backup when the coil is hot I suspect the air will be much hotter and I also suspect the flow to increase once the coil is warm as gravity will be helping. On the coldest of days I am worried that there won't be enough airflow to offset the heat loss, we'll see what happens. I'm hoping the increased duct temperature will offset the reduced flow, if it gets realllly cold (extended periods of below zero) I might raise the boiler temperature to 210 or so. If I was to guess, I'd say the original furnace supplied 1800CFM @ 120-150 degrees, I suspect the coal boiler to produce duct temps in the 150-180 degree range at 1000 cfm. The basement should be much warmer which should help out everything.

Yanche wrote:This has got to be one of the first water coil installs described on this forum. At lease to this level of detail.

I've used this system for 4 years and it works very nicley. My heat exchanger is in the return but the net result is the same. I use tempered water and run the blower motor constantly. It's a very even, comfortable system.

As it gets really cold something you can try is running your furance fan longer, at lower speeds. The coal is always burning, keeping it long and steady might work for you.

Now if your coal boiler's BTUs are rated near what your propain furance is... you shouldn't have any problems. When a stoker is roaring, feeding steady... they really make some heat.

e.alleg wrote:The basement should be much warmer which should help out everything.

This alone will change the character of your heated home. There will be more even temps and less drafts. You may have a little fine tuning, but you have arrived!
You have spent too much time worrying about this, in a month you will be grinning ear to ear.

A set of shut off valves at the coil will prevent the coil from carring away heat to the coal boiler when it is down and you run your propane boiler.