HVAC help regarding pre heaters and there need.

[roopi]

Our home was a new build and is 3.5 years old now. I've never owned a home with a pre heater before so I'm not familiar with their need. As far as I know it pre heats fresh air before it hits the furnace. I believe the main reason this was installed is due to the over size hood fan we have but that is just a uneducated guess.

18 months ago the preheater caught fire and luckily we were home and caught it before it spread. The basement had filled with smoke but I was able to turn the furnace off which killed the power to the preheater.

The builder came back and replaced the unit assuming it was faulty. Two nights ago we started to smell burning plastic and again it was the preheater melting. There were no flames but still a scaring situation.

The builder is coming out again with the HVAC company and electrical company. As of now I told the builder I don't want a preheater in the home as my wife doesn't feel safe since this has happened twice.

The builder said he mentioned this to the HVAC company and they think we should have it as it could cause other issue by removing it. They will provide me with more info when they come out for a site visit but I'd like to be prepared before I speak with them.

Can anyone offer some advice on the need for a preheater or past experience with Thermolec Pre Heaters. Do I request a different preheater? Do I have it removed? Any info would be appreciated.

[R154]

1 can be chalked up to a production fault. 2 means there is a problem with the control wiring or more likely the voltage supplied.

Did the vendor tell you what failed? The core or the voltage regulator? Do you know how it was wired?

Very odd.

[roopi]

Originally posted by R154
1 can be chalked up to a production fault. 2 means there is a problem with the control wiring or more likely the voltage supplied.

Did the vendor tell you what failed? The core or the voltage regulator? Do you know how it was wired?

Very odd.

I never did follow up on why the original failed. My fault for sure. I'm meeting with them this week so I will definitely question that. When you ask do I know how it was wired what do you mean? I looked at the wiring documentation and it looks correct. As for power to it, it is on its own double breaker.

After the first fail they explained to me it only turns on when my hood fan is on level 4 (highest setting) however I didn't even run the hood fan the day of the second fail so it shouldn't have even been on that day. This is something I have already questioned but they haven't provided any answers yet until the site visit.

Some additional info the inside of the unit is labeled 'Thermolec Standard Fresh Air & Zone Heater 208 / 240'

[R154]

So it's a 3phase heater.

Control wiring is what goes between the heater processor and the aircon controller.

The electriciaan will be able to tell if they wired the heater backwards. It's odd that there isn't an overheat protection sensor/circuit. Sounds like the unit overheated.

[legendboy]

Any sort of heater with any kind of intertek, csa, ul, cul label on it should have a high limit switch integral.

[R154]

Right?

I wonder if it was wired 1ph 24p in stead of 3ph 240.

[Maxt]

Model #?
If this a thermo-air TER model, make sure the temperature sensor for the modulating control is on the air out side. The sensor has 2 possible mounting positions depending on which way its installed. If if the sensor is on the inlet, it will overheat. I never liked thermolec's solid state airflow sensor either, I always use an air proving switch with them as added safety, I had one of their larger heaters that kept coming on with only about 5% of the heaters rated airflow.

[Crazyjoker77]

Originally posted by R154
So it's a 3phase heater.

Control wiring is what goes between the heater processor and the aircon controller.

The electriciaan will be able to tell if they wired the heater backwards. It's odd that there isn't an overheat protection sensor/circuit. Sounds like the unit overheated.

Originally posted by R154
Right?

I wonder if it was wired 1ph 24p in stead of 3ph 240.

The fact that is says 208/240 says that its single phase not 3phase and that the OP's 2 pole breaker is correct.

There is no such thing in north America as 3ph 240. His heater can be either hooked up to a regular residential panel at 240 or use 2 hots from 120/208 3ph panel giving you single phase 208.

[R154]

I meant 3ph 208.

[frozenrice]

On the topic of whether or not you need the preheater, it's there like you said because of the capacity of your hoodfan.
When the capacity of your hoodfan exhaust exceeds over 600cfms, you need to balance the air being exhausted with adequate fresh air otherwise you end up with negative air pressure inside the house which can draw the exhaust air from your furnace exhaust back into the house (ie carbon monoxide). To do this the hoodfan is wired so the furnace kicks in to draw in the air. This process is known as a makeup air setup. When it's bitterly cold out like -30C, you don't want to circulate cold air through the house, so the heat exchanger on the furnace will kick in to do what it's supposed to do, heat the air. However, in order to burn natural gas, you need combustion air intake (separate system from the fresh air that circulates through the house). If the combustion air temperature is cold enough, it can cause damage to the heat exchanger in the form of condensation, which then in turns rusts out and could cause combustion issues such as O2. The reason for a preheater is to do exactly as it says, preheat the combustion air so that it is warmed up before hitting the heat exchanger on the furnace.

There are a few options you can go with:
1) Ask for a different brand/kind of preheater/set up if you keep your current hoodfan.

2) Remove the preheater, but along with that you'd have to downgrade your hoodfan to a smaller capacity.

[roopi]

Originally posted by Maxt
Model #?
If this a thermo-air TER model, make sure the temperature sensor for the modulating control is on the air out side. The sensor has 2 possible mounting positions depending on which way its installed. If if the sensor is on the inlet, it will overheat. I never liked thermolec's solid state airflow sensor either, I always use an air proving switch with them as added safety, I had one of their larger heaters that kept coming on with only about 5% of the heaters rated airflow.

It is the Thermolec FC-TER-8-3208 so yes it is the model/type you are referring to. I did find the link below explaining what you are referring to about the sensor and I will be checking it tonight to see how it was setup.

http://www.thermolec.com/_documentat...ril%202007.pdf

Also looking at this documentation it is showing the default air flow is from right to left. In my home the air flows from left to right so I'm wondering if they changed the setting for this when installing. Again I'll check this tonight. There are a couple pictures below from both units that failed but I'm not sure if it is set correctly from the pictures I have with me.

First Unit that failed:



Second Unit that failed:

[roopi]

Originally posted by frozenrice
On the topic of whether or not you need the preheater, it's there like you said because of the capacity of your hoodfan.
When the capacity of your hoodfan exhaust exceeds over 600cfms, you need to balance the air being exhausted with adequate fresh air otherwise you end up with negative air pressure inside the house which can draw the exhaust air from your furnace exhaust back into the house (ie carbon monoxide). To do this the hoodfan is wired so the furnace kicks in to draw in the air. This process is known as a makeup air setup. When it's bitterly cold out like -30C, you don't want to circulate cold air through the house, so the heat exchanger on the furnace will kick in to do what it's supposed to do, heat the air. However, in order to burn natural gas, you need combustion air intake (separate system from the fresh air that circulates through the house). If the combustion air temperature is cold enough, it can cause damage to the heat exchanger in the form of condensation, which then in turns rusts out and could cause combustion issues such as O2. The reason for a preheater is to do exactly as it says, preheat the combustion air so that it is warmed up before hitting the heat exchanger on the furnace.

There are a few options you can go with:
1) Ask for a different brand/kind of preheater/set up if you keep your current hoodfan.

2) Remove the preheater, but along with that you'd have to downgrade your hoodfan to a smaller capacity.

I appreciate the explanation. I don't want to downgrade the hood fan. So I will see what my options are regarding a different brand or any other options to keep the current setup.

My guess is that something was setup/installed incorrectly which is causing this issue. I'll see what I can determine tonight when looking at it again.

[Maxt]

Here's something goofy, the Ter3208 is rated to draw 14.4 amps and be on a 20 amp breaker, while the spec sheet for the D21-T controller says the controller is only good for 12.5 amps.

http://www.thermolec.com/_documentat...20specs240.pdf

They make a unit specifically for 240v that is different, I do believe Calgary residential is 240v, I don't live there, so I can't say for sure, but if so the heater should be a TER-3240 which has lower amp rating of 12.5. Usually stuff is rated 208/240, but something is different if they are offering voltage specific models.

[roopi]

Originally posted by Maxt
Here's something goofy, the Ter3208 is rated to draw 14.4 amps and be on a 20 amp breaker, while the spec sheet for the D21-T controller says the controller is only good for 12.5 amps.

http://www.thermolec.com/_documentat...20specs240.pdf

They make a unit specifically for 240v that is different, I do believe Calgary residential is 240v, I don't live there, so I can't say for sure, but if so the heater should be a TER-3240 which has lower amp rating of 12.5. Usually stuff is rated 208/240, but something is different if they are offering voltage specific models.

This is over my head but I'll bring this up with the electrician on Thursday I guess.

In addition I did check the location of the temperature sensor and it is correct.

[legendboy]

Originally posted by Maxt
Here's something goofy, the Ter3208 is rated to draw 14.4 amps and be on a 20 amp breaker, while the spec sheet for the D21-T controller says the controller is only good for 12.5 amps.

http://www.thermolec.com/_documentat...20specs240.pdf

They make a unit specifically for 240v that is different, I do believe Calgary residential is 240v, I don't live there, so I can't say for sure, but if so the heater should be a TER-3240 which has lower amp rating of 12.5. Usually stuff is rated 208/240, but something is different if they are offering voltage specific models.

Have you seen many residential units fail like the ones in the pictures?

This looks like pretty scary damage to me I have been dealing with CCI forever, i'd be making some calls if it were me. Something not right for it to catch fire instead of just tripping OL or OC. I'm not even sure a proving switch would have done any good here??

OP your high limit is located just below the white ceramic components.

[Maxt]

Originally posted by legendboy


Have you seen many residential units fail like the ones in the pictures?

This looks like pretty scary damage to me I have been dealing with CCI forever, i'd be making some calls if it were me. Something not right for it to catch fire instead of just tripping OL or OC. I'm not even sure a proving switch would have done any good here??

OP your high limit is located just below the white ceramic components.

I've seen commercial duct heaters all burnt on the element side, adding the air proving switch put a stop to some repeated limit trips and element burn ups... The airflow sensor they use will bring on the heater with a wisp of air moving.
This particular situation though, looks like the control can't handle the full load amps the heater is drawing, and its just plain all out weird that Thermolec, by their own literature, is over taxing their own control.

[roopi]

I had a site visit with the builder, HVAC installer, and electrician yesterday.

From questioning the HVAC installer on how/when this unit works he explained to me that when the preheater senses air flow it turns on. It should sense airflow when the hood fan is on its highest setting since this is when the interlock opens up for the makeup air.

Questioning the electrician he said the wiring for the unit is correct. If there was an issue with the wiring there would have been damage to the main power wires coming into the unit and not the area that is melted.

So the first the time the unit caught on fire we had just finished cooking dinner and we were using the hood fan. On the second occasion the hood fan was not used. I don't think it had been turned on for days. So the unit does have constant power to it and the only thing I could think of is that it is sensing air flow when the furnace is turning on/off causing the preheater to keep turning on and off. There is enough airflow to turn it on but not enough to keep the unit cool?

So looking at my current setup, between the preheater and furnace is an inline fan that turns on with the hood fan. If they wire the preheater to only receive power when the inline fan turns on I think I shouldn't have this problem with the preheater since it takes out the need for the airflow sensor controlling the unit.

[Crazyjoker77]

Originally posted by roopi
I had a site visit with the builder, HVAC installer, and electrician yesterday.

From questioning the HVAC installer on how/when this unit works he explained to me that when the preheater senses air flow it turns on. It should sense airflow when the hood fan is on its highest setting since this is when the interlock opens up for the makeup air.

Questioning the electrician he said the wiring for the unit is correct. If there was an issue with the wiring there would have been damage to the main power wires coming into the unit and not the area that is melted.

So the first the time the unit caught on fire we had just finished cooking dinner and we were using the hood fan. On the second occasion the hood fan was not used. I don't think it had been turned on for days. So the unit does have constant power to it and the only thing I could think of is that it is sensing air flow when the furnace is turning on/off causing the preheater to keep turning on and off. There is enough airflow to turn it on but not enough to keep the unit cool?

So looking at my current setup, between the preheater and furnace is an inline fan that turns on with the hood fan. If they wire the preheater to only receive power when the inline fan turns on I think I shouldn't have this problem with the preheater since it takes out the need for the airflow sensor controlling the unit.

I'm with Maxt on this one.

Even in worse case scenario of both inlet and outlet blocked and the controls stuck to full heat the unit shouldn't burst into flames. The high limit should trip long before anything gets to a combustion temp.

The issue seems to be with the controller itself (d21-T) which the high limit doesn't monitor. Its either as maxt says its under rated for the power of the heating element(s) or its just a bad batch of controllers.

In picture 1 the unit only has a single element but in picture 2 it has 2 so they changed it with a different model #

Is this thing stamped CSA approved?

After a quick read of the manual airflow really doesn't matter as it ramps down the heat with airflow and maintains a constant discharge temp. Hence the need for the fancy controller and air sensor instead of a simple relay and sail switch and of course failing that the high limit will trip before anything gets hot enough to catch fire. changing the interlock systems isn't going to help.

[jeffh]

Where does the preheater piping hook up to inside your home after the inlet from outside? I assume it is hooked up directly to your furnaces return air line. And if so, if your furnace blower ever tufns on, then it would consequently pull air through the electric preheater. Also, if you turn on any bath fan or the hood fan at a lower setting, it may still trip the electric heaters flow sensor, if they are as touchy as maxt says they are. The heater could be turning on too often and during undesirable flow rates.

[legendboy]

anything from thermolec will be csa/intertek

who is the mechanical doing your hvac?