Cleaning Heat Exchanger

[Trevdor]

Hi! So I’ve been having trouble with my Hardy outdoor wood heater, can’t get the inside temp in the house above 66. With some help from you all I think I’ve eliminated that it could be air in the line or a problem with the heater itself. I think the next thing I’m going to try to do is clean the heat exchanger. We’ve been in the house 5 years and never cleaned it and I don’t believe it was ever cleaned by the previous owners. We have hard water so I’m wondering if that is what it is.

There is no easy way to get to the heat exchanger though, I’d have to remove a lot of the duct work. Is it possible to just remove the in and out water lines and pump something through it to clean it? Was thinking of using CLR or vinegar. Or would I be better off taking it all the way out and soaking it?

Thanks!

 

[maple1]

Yes it is possible to do the CLR thing. But I don't think a flow issue was completely ruled out. Or bad underground pipe.

 

[yooperdave]

Are you speaking of a water to air heat exchanger? (called a hot water coil) or a water to water heat exchanger?

I had an OWB for decades installed for a forced air system using the HWC and never had to clean the heat exchanger.....

Does that hardy have a heat exchanger on it that needs to have the ash cleaned out from it? Not in the fire box itself, mind you.

I thought some of those hardys had a plate that you took off and had to brush out the tubes?

 

[Trevdor]

Yeah, I’m still totally open to suggestions. I’m not sure how to test the flow, but we are only losing 2 degrees of water temp from the Hardy to inside. Then about 10-13 degrees over the heat exchanger or hot water coil. We are going from hot water to hot air so does that make it a hot water coil then? All this is new to me. My thinking was that with only losing 10 degrees of heat that we aren’t getting enough heat transfer, so maybe due to the hard water we have lime or calcium build up which is killing the efficiency of the

I don’t believe the Hardy H4 has a plate that needs brushed off, at least I hope it doesn’t! The only thing I clean ash out of is under the grates where the wood burns.

Thank you all for your time and suggestions.

 

[maple1]

The 10 degrees could be totally normal. It also depends on air flow through the exchanger.

I never saw temps posted on the other threads. How did you measure them and where? It's easy to get inaccurate ones. You also need to measure temps in and out of everything the water goes through.

 

[Trevdor]

Airflow has never been great as it’s a hundred year old house, but it seems like the same as in past years.

I used an infrared gun to test, which I think is pretty accurate, but I can strap a kitchen thermometer to them and see what that gives me. I tested outside coming out of the pump and inside going into and out of the heat coil / exchange.

 

[brenndatomu]

10-13 degrees over the heat exchanger or hot water coil.

Sounds low to me...I would think its gonna take 3 times that to heat the house well.

I used an infrared gun to test

Keep in mind, those are only completely accurate on smooth, flat black surfaces...you can either put some black electrical tape on the spot you are trying to test, or just spray some flat black paint on it.

 

[maple1]

Yes, IR guns can be difficult. Or mine is anyway. Definitely not good on shiney surfaces. I would be using a dual probe bbq thermometer with the probes under a bit of pipe insulation.

 

[yooperdave]

What is the temp of the supply side entering the "heat exchanger" (HWC) compared to the leaving temp?

 

[yooperdave]

What is the temp of the supply side entering the "heat exchanger" (HWC) compared to the leaving temp?

What I'm asking, is the supply temp at 150f for example and leaving 137f? I see above you already stated about 10-13 temp difference....

If you feel this is the source of the problem, there are a couple things you can do now.

Make sure your air filter for the furnace is clean.

Make sure the HWC is clean. It is possible that the outside of the HWC could be partially dirty/clogged and would require a good cleaning.

Understand that I am thinking that your HWC is like a radiator, right? It would look similar to this and probably in a horizontal position inside your plenum.

If this is your setup, and everything is clean, I think you should lower the speed on the blower motor which delivers the warm supply air to the house. By lowering the speed, it moves less air across the heat exchanger. This allows that air to absorb more heat from the HWC.

 

[maple1]

Airflow has never been great as it’s a hundred year old house, but it seems like the same as in past years.

I used an infrared gun to test, which I think is pretty accurate, but I can strap a kitchen thermometer to them and see what that gives me. I tested outside coming out of the pump and inside going into and out of the heat coil / exchange.

What I was referring to is airflow through the exchanger, which isn't related to the age of the house. Which could decrease over time from dust/dirt on the hx fins, or dirty air filter, or some kind of fan issue.

But it still all comes back to and starts with accurate temp measuring everywhere first to try to see how the hot water is or isn't doing. Then go from there.

 

[Trevdor]

I tried to get temp readings this morning, but the thermometer we have wasn’t ideal. I’ll pick up a different one today and try again.

I was also able to open my vents a bit to at least look at the heat exchanger. It is a bit dusty, but doesn’t look to bad I guess. Could I use some compressed air to blow what dust is on it off? The air filters were changed not to long ago, I’ll admit that I’m not very good at remembering to change them regularly though.

 

[yooperdave]

Are you able to select a slower blower motor speed? The coil doesn't look dirty from what I can see. It should be positioned so that no air can bypass around the edges of it; the air has to pass through the coil.

 

[Trevdor]

I can’t change the blower speed as far as I know, but I could be wrong. It’s an old system tied into a fuel oil system as a backup. I’ll have to double check at lunch if air can get around the heat exchanger.

Thank you all again for the help.

 

[brenndatomu]

It’s an old system tied into a fuel oil system as a backup.

I bet its an old belt driven blower with an adjustable pulley on the motor...if its a direct drive the motor likely has 3-4 different speed taps...either way its not the simplest thing to change if your aren't familiar with it...

 

[yooperdave]

What temp is your OWB set to?

When did you begin to notice the house wouldn't get warmer than 66? Did it coincide with some colder temps in your region? I

Is it possible to turn up the temp of the OWB?

I would run mine (central boiler) at 165 until we got a cold snap of below zero for a few weeks. Then, I would bump it up by 10-12 degrees.

 

[yooperdave]

Is this the first year with this heating setup or the first year with the residence?

 

[brenndatomu]

I would run mine (central boiler) at 165 until we got a cold snap of below zero for a few weeks. Then, I would bump it up by 10-12 degrees.

I think 180* is pretty common when it gets real cold, no?

 

[yooperdave]

I think 180* is pretty common when it gets real cold, no?

Yes.

 

[maple1]

Is this the first year with this heating setup or the first year with the residence?

I think from memory of the other thread, it's been in service a few years.

 

[yooperdave]

I think from memory of the other thread, it's been in service a few years.

I wonder if the heat load on the house changed? Maybe it got colder there all of a sudden? What kind of shape is the house in? Older? Insulation amounts? Lots of variables......

 

[Trevdor]

Thank you all for all your replies! Sorry I started another thread, didn’t think it would blow up like this, but I appreciate it.

It’s a 100 year old farm house, we’ve been here 5 years and have had to do minor repairs on the wood heater like replace the pump and aquastat. This is the first time this specific problem has presented itself. We used our fuel oil system up until a couple of weeks ago when the temperature really dropped and we started the wood burner.

I got a meat thermometer and just to test when I put the water thermostat at 160 and measure the water temp when the fan cut off it was 153 on the meat thermometer and 155 on the infra red, that was coming right out of the pump. It was just a couple degrees lower than that inside, and then a 10-13 degree drop to over the heat exchanger. Normally I’ve had the water temp set at 170.

Tomorrow is actually going to be a warm day, if I was going to do anything to the heat exchanger / coil, doing it then would probably be best. Do you all think it’s worth trying at this point?

 

[maple1]

So 150 +/- going into the HX? That's not really very hot. Almost sounds like you just need to turn the temp on the boiler up. I would not tear into the HX. Certainly not yet anyway.

 

[maple1]

What is the temp of the return water at the boiler just before it goes back into it? When supply coming out of it is 153?

 

[Trevdor]

What is the temp of the return water at the boiler just before it goes back into it? When supply coming out of it is 153?

I only had it at 160 to test it. I bumped it back up to 170 and the water temp was measuring 169 coming out of pump. 167 going into heat exchanger in the house. 155 coming out of it, and 153 back at the wood heater going back in.