The $800 Resistor Pack

Back in 1999 I had a house built. That wound up being an extremely stressful time in my life, as we’d also just moved to the Nevada City area, and my wife was pregnant. Word on the job site was that several sub-contractors bet the under for our marriage surviving, but that which does not kill us makes us stronger.

Once the house was actually done, life became much better. And we’ve been very, very happy with our house. Other than one thing. As that famous bard once wrote, “The first thing we do, let’s kill all the HVAC companies”.

I’ve got a panel house, built from SIPs – structural insulated panels. Very efficient, and very air-tight. The two kind of go hand-in-hand. Which means we need make-up air, a steady stream of fresh goodness from the outside so our dog’s fart doesn’t stink up the place for two weeks. Plus you can get sick house disease, where carpet chemicals, mold, and diapers can make you physically ill if you don’t get enough fresh air on a regular basis.

But when you bring fresh air in, old air has to go out. And this old air is air that we’ve carefully, painfully heated (or cooled) using natural gas or electricity. So venting air is essentially throwing good money and precious energy out the window – kind of like running the A/C with the front door open.

Enter something call an air-to-air heat exchanger, or heat recovery ventilator (HRV). This forces the air we’re venting to flow next to the air we’re pulling in, so that some of the energy we’ve expended to heat or cool the air inside the house gets transfered to the fresh air being pulled in from the outside.

So far, all good. Sounds like a great idea. And in theory it is. But then there’s reality:

  1. We wanted a 220 CFM (cubit feet/minute) HRV unit with 74% efficiency and a 320 watt power draw. The efficiency tells you how much of the potential energy is extracted from the inside air on its way out. The watts tell you how much power is needed to run the fans that pull and push the air through the system.
  2. What we got was a Carrier HRV model VC5BAB027000. This is a 200 CFM HRV unit with 68% efficiency that draws 500 watts. Unfortunately the general contractor signed off on this change, without talking to me or the engineer who did the energy calcs and drafted the original recommendation.
  3. After calculating the electrical cost of running the unit during the fall/winter, when compared to the cost of using gas to heat the air, we’re breaking even for half the year. And that doesn’t include the cost of the unit. If we were just basing it on energy cost, then you’d still have to factor in the energy required to build the unit, which is huge when it involves metal fabrication.
  4. Oh, and this unit had been discontinued two years before we had it installed. So the spare part situation was already heading downhill (see below) by the time we first switched it on.
  5. When I was trying to do the calculations for energy savings (above), I contacted Carrier to get the full specifications. Nope, can’t do that. I’m not a certified Carrier dealer. Now that just feels wrong. If I bought the unit, why is it OK for a company to refuse to send me information that I need to correctly operate it? This bugged me so much that I worked my way up through Carrier to the office of the president, but then the customer defense system proved too strong, and I was forced to admit defeat.
  6. Then the unit stopped working. About two years after the five year warranty expired. Nice. What failed were two relays on the circuit board. I’ve included the photo below, so you can understand why it makes sense for Carrier to charge $812 for a replacement. I mean, the relays alone are almost $3.

Carrier HRV Board

Now I’m not an electrical engineer, so perhaps my reasoning is off, but it looks to me like this board has got about 12 resistors, 13 diodes, 10 capacitors, three relays, two ICs, and a transformer. Total cost would be in the range of $5 – $10. Heck, I even looked up the price for the relays – $1.29 full retail per.

What’s interesting (as in the Chinese curse of “may you live in interesting times”) is that for parts distributors that have this in stock, it was $280, then $350, but now if you want it from Carrier it’s $812. Seems pretty clear that they’ve got a limited supply of these boards left, and the price heads up as boards get sold. Which, from a pure economic model makes sense, but from a customer loyalty perspective is dead wrong.

I’m in the midst of a startup ( so my free time is virtually non-existent, but I’m still tempted to buy the two relays and try to replace them myself. There’s no way in hell I’m going to pay $812 for that board, so the other option is to throw away this $2400 unit and replace it with something new. The only bright spot is that I can get a more efficient model, with the air flow that I want, for about $1100 plus installation.

Anyway, a friend said that the fundamental problem is that HVAC companies are in the business of selling sheet metal, but they don’t want anybody to figure that out. So they create a closed network of dealers, restrict the flow of information, and pray each night that they don’t get hit with a consumer rights class action lawsuit.

6 Responses to The $800 Resistor Pack

  1. kkrugler says:

    Update – the original HVAC company agreed to get me the board at their cost, which was still a bit under $300. I installed it, and everything seems to be working OK – other than the fact that it was running continuously. But then my wife figured out that one of our HVAC controllers had the fan set to “on” instead of “auto”…wish I’d checked that before I started crawling around under the house.

  2. Steve Lewis says:

    Hi, Accidently ran into your post re HRV’s. Just tonight I was looking at mine as it has not been working for several years and I just had not F/U’d up on it. The damn thing is about 10 years old and in brand new condition, but has not been working for past 8 yrs. Quite a coincidnece…I designed and built a SIP house of about 4ooo sq ft and like it very much. BTW,I live in Chesapeake, VA. I want to get this unit fixed if possible, but your situation with Carrier doesnt sound good. I went to check it myself tonight. It’s getting power, etc. but came to pretty much a dead end due to electronic circuit board. Was just looking on carrier site and for local factory reps. May call one in a day or two…need to find out what is wrong before I can do anything. May be an easy fix. Am eventually going to sell this house and am designing my next SIP house which will be even better than this one. If you can offer any advice re HRV or just want to discuss SIP contact me at Regards, Steve

  3. kkrugler says:

    Hi Steve,

    One bit of advice, at least if you’ve got a two-story SIP house, is to ensure that (a) you have a two zone system, and (b) you can configure the HVAC controller to ensure that the fans are running some reasonable percentage of the time (e.g. at least a 15% duty cycle).

    If you don’t do this, then the air in house tends to stratify. The situation we were running into during the summer was that the A/C wouldn’t run during the day, but suddenly at midnight it would start up. Which was very confusing, since the area we live in has low night-time temperatures (e.g. 50°F) in the summer, even if it reached 100°F during the day.

    After some head scratching and measurements, eventually it became clear what was going on. The SIP house is like a well-insulated ice chest that’s left out in the sun. During the day it warms up slowly, which is great. But eventually, because it’s so well insulated, the energy (heat) that’s accumulated inside the house during the day won’t escape quickly when the outside temperature has dropped. This energy eventually flows up to the second floor as warm air, and the temperature finally gets high enough to trigger some A/C activity.

    A whole-house fan would help here, but due to allergies that’s not an option for us. So I wound up doing two things.

    First, I bought an AirCycler, which is a 3rd party unit that attaches between the HVAC thermostat and the HVAC controller. It can be programmed to ensure that the fan runs at least X% of the time. Using this, I could keep the house air mixed so that we didn’t wind up with all the warmer air upstairs (where our bedrooms are located) at night.

    Second, I changed the timing of the thermostats to really cool the house at night, down to 55°F. This was fairly efficient, since the outside temperature is so low then as well, which means the condensor for the A/C doesn’t have to work as hard. By pre-cooling the thermal mass of the house, we could get through most days without any A/C during the day, until we started the cooling cycle again at around 10PM.

    Hope this helps,

    — Ken

  4. Gary VDW says:


    I have the same HRV, I had it put in back in 1998, it quit working 2 months ago. I pulled the curcuit board off and found the same as you- relays appeared burned and non-working. In my case, the relays did work, they had lost contact with the board conductivity strips. I could see the burn marks where the relays were soldered on the board. Took it to my barn, tried to repair the solder joints but that didn’t take. So I soldered a jumper wire between the two points and it took right off working fine. I also called my local Carrier dealer, cost for new board was $750. For that much, I can get a few relays from Radio Shack and have a working unit for $5 and a little solder know-how. Really dusted me to know how Carrier backed up it’s product. I have Carrier A/C, that is working well, but this board issue has left a sour taste in my mouth for Carrier equipment. Thanks for your original post, hope things are going well for you now.

    Richland, MI

  5. brent says:

    You’ve got it all wrong. I own a PPV system in NZ. The airflow in was via filtered air from the heated roofspace on days where solar energy made it warmer than the house 8/10 and it dumps it in raising my house by about 3-4%C by the time I get home. Then I just add a degree or two to top up with a basic heater. Simple and cheap. 1st winter used I saved $575 over previous year in heating costs in a colder winter – proving then, that they do wrok.

  6. kkrugler says:

    Hi Brent,

    Not sure what you’re referring to when you say “You’ve got it all wrong.” From what I can tell, you’re talking about how to heat your house during the winter. And yes, my HRV does reduce my gas heating cost, but the electrical charges are higher than the savings, so the net outcome is that it winds up costing me money during the winter.

    During the summer it’s a slight win, since I’m paying for electricity to cool the air w/my A/C system.

    — Ken

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