Bad Install of ERV in Attic
bsawers
| Posted in Mechanicals on
In 2014 (before we bought this house) a HRV/ERV was installed in the attic. But, it was installed wrong since the exhaust and air intake are located inside the attic. The obvious solution is two holes in my roof. Before I do that, I would like an expert opinion. So far, I haven’t been able to find an HVAC tech with any experience. The house is located in Maryland, very close to both DC and Virginia. Any suggestions for local expertise would be very much appreciated.
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We use WH Metcalfe for ERVs. They should be able to offer some guidance.
Can you post a few pics of the unit, and your attic? Does it have gable end walls?
Given the install scenario, my guess is that there are other issues as well that you'll need some experience on site to address.
Since you mentioned holes in you roof, I'll point out that typically intakes are avoided in your roof especially with asphalt shingles. I believe they offgas when they get hot and you don't want to suck that air into your house. Shoot for a gable end.
Thanks the recommendation. I will call WH Metcalfe.
To DennisWood and stevedavis, I have included a picture, I don't know if any capture the installation. Unfortunately, the roof is hipped, so there's no gable to avoid the shingles.
Despite the ridge vents, eave vents, and insulation, this attic overheats in summer. Just now, it was warmer than I'd prefer.
The purpose of attic ventilation isn't to keep the attic cool, it's to keep moisture from accumulating.
Since my HVAC is located inside the attic, I'd like to keep it cooler in summer. Also, I imagine the cooling load for the second floor will be lower if it's not overheated inside the attic.
Ventilation is not the way to do that. You want to get insulation between the HVAC equipment and unconditioned space. You can either insulate and condition the entire attic, or build an insulated enclosure just around the HVAC equipment.
And this ERV fresh air intake is pulling air from your attic space? Yikes.
You’ll want to also look at options for relocating the unit itself into conditioned space, or creating one in your existing attic space.
Relocating would solve the other problem which I think it condensation-related. I have seen no evidence of a problem yet but I believe it's a potential problem with unconditioned attic installations.
When I asked for advice on insulating the entire attic to bring the entire space within the building envelope, I was told it was a bad idea. Right now, the attic is supposed vent, but you can tell from the interior temperature that too little air is moving.
On a hot day, an unconditioned attic like that would easily be in the 120F range, likely more. I'm no expert on building code in Maryland, but I'd guess that the entire HVAC setup would be a fail there as it would here. Without knowing what the building layout is, it may very well be more cost effective to convert that attic to a conditioned space, vs redoing all the mechanical up there.
More venting won't fix the issue. With an un-vented approach (spray foaming the roof deck + ignition barrier), there would be no vents at all, and you'd be making the attic part of the conditioned house. If I had to guess, I'd say your AC costs must be high?
The house has two HVAC systems. One of the systems is located in the attic and it certainly cannot be moved. I believe the HRV/ERV might be movable.
Instead of spray foaming the roof deck, what do people think of insulating on top of the sheathing? My first choice is a double-roof, where air can flow between the two layers. But, I have been told that's very expensive, if not too novel for anyone to agree to build it.
Insulating over the sheathing is legit, when you're reroofing.
Another approach is to build a "dog house" inside the attic for the HVAC equipment.
There are quite a few articles here on insulating over roof sheathing, and it would give you the option of using Rockwool for a less carbon intense approach.
Dennis,
With all respect, I would check your facts on saying Rockwool is greener than foam board. Efficiency Vermont published a study you can find at this link below which clearly states it has a higher carbon cost than polyiso and EPS. It does beat out XPS though; even the HFO-based XPS is pretty nasty stuff.
Heating up slag to 3000 degF takes a lot of energy. I have no idea where the rumors of Rockwool being green originated from. Probably just some good marketing on their part. One of those pet peeves for me, sorry for ranting here.
https://www.efficiencyvermont.com/Media/Default/docs/white-papers/The_High_GHG_Price_Tag_on_Residential_Building_Materials.pdf
(See Table 1 on Page 9, GWP* column)
Good point Matthew...like many, I get caught up on the XPS numbers.
For the record, I think insulating your roof deck (where a vented attic exists) make zero sense from both the cost and risk viewpoint. Creating a conditioned "dog house" makes more sense, however it increases the risk that things like HRV filters are not regularly removed and cleaned if say a ladder is required to access it. Even with units installed at eye level in a furnace room, I've seen a few that had near zero flow because they were never opened to clean :-(
I called WH Metcalfe who said they only do new construction, so they recommended CroppMetcalfe.
The CroppMetcalfe tech thought the installation was fine, except that the intake and exhaust were reversed. The intake is supposed to join the ductwork closer to the air handler than the exhaust. He seemed to think that an intake terminating 18 inches from a turbine vent was fine. He was concerned about the drain hose freezing, but insisted the loop was correct. Lastly, he thought it was fine that the entire HVAC system was located inside an unconditioned attic.
I asked him about adding a sytem for the basement and main floor (two zone, different system). But, the furnace and water heater exhaust right where the intake would go. He didn't seem to know anything about systems that rely on their own ductwork, like Zehnder.
The HRV/ERV hasn't been used in a year. I was going to try it for a little while, even though I am concerned about bringing air from the attic into the house.
If the tech is wrong about HVAC systems in unconditioned attics, one option is insulating the attic (either foam inside or rockwool outside) and sealing the eave vents, aside from a few that could be used for the HRV/ERV intake and exhaust.
Any thoughts?
"Lastly, he thought it was fine that the entire HVAC system was located inside an unconditioned attic."
To me this suggests he's just your typical run-of-the-mill HVAC tech using rules of thumb. Probably also thinks it's fine to size an HVAC according to the 1 ton per 500 sq ft rule. "Well, everybody else does it, so this is fine."
An HVAC in an unconditioned attic is only "fine" if your definition of fine is "common." But in terms of efficiency and comfort, it's about the worst place to put one.
It's possible the guy could be extremely competent with ERVs, but what you've described does not inspire much confidence.
..and an ERV intake pulling air from a hot attic makes absolutely no sense..
The only time insulating the roof makes sense is if you want to use the attic for living space or storage.
The best would have been not to install any equipment there but that ship has sailed. The best you can do now is to improve the existing setup.
First step from the picture, it looks like the air handler is not insulated. This a big heat loss in the winter time and condensation risk in the summer. The air handler should be wrapped with insualtion (not reflective bubble wrap).
The HRV drain in an unconditioned attic is an issue in colder climate, I'm in zone 5 and it won't work here. You are in warmer climate and it might be OK there but still a risk. The simplest would be to see if you can swap the HRV core for and ERV, this would avoid the need for a drain. If this can't happen, you can wrap in the drain in insulation which hopefully will keep it warm enough not to freeze.
The HRV intake should absolutely not be from the attic. The simplest is to run to the soffit and install an intake there. The exhaust can go to the turbine vent but really it should also be run to another soffit vent about 6' away from the intake.
Once this is all done, find somebody that with a duct blaster and test all the ducting for leakage and seal it up.
P.S. During duct blaster testing, the HRV intake and exhaust are leak paths, the tech might need to disconnect these and cap them temporarily.
The air handler is not insulated. Wrap makes me think that the insulation would extend below the air handler. Or am I just insulating the three exposed sides? If I shouldn't reflective bubble wrap, what's a good product or approach?
For relocating the intake to the soffit, what's the best way to terminate the intake? I assume there needs to be a sealed connection, otherwise I will be drawing from the soffit-adjacent insulation rather than the center of the attic like now.
The drain has a loop, which I'm not sure I understand. The tech said it was necessary to provide a trap, but the drain just empties into the basin underneath the air handler. What's the need for a trap?
The loop is there to keep water in the line. The resting water level in the loop should be just above where the two drains T into one. This keeps higher pressure on one side of the core from "backing" up via the drain hose to the low pressure side of the core. If you don't have the loop, water can back up in the HRV drain pan.
Relocating the intake to the soffit means connecting the intake duct to a soffit hood installed external to your soffit. They look like this: https://www.primexvents.com/product-details/sv28-soffit-intake-and-exhaust-vent/
I would be connecting the exhaust up as well, to another soffit vent, at least 10 feet away if that works for y0u.
If that is a fuel burner than it generally can't be insulated. If it is a heat pump it can be insulated with duct wrap (shiny foil on the outside and fiberglass on the inside) or with foil faced rigid insulation. The insulation should be put in a such a way as you can still access the unit for service. You do want all the sides wrapped and taped up to air seal.
Insulating the air handler is less important than air sealing all your ducts, duct blaster is what you want to focus on.
Heat tape on the HRV drain can work but you have to also install heat tape on all the sections in the attic that lead to your plumbing drain. If the HRV dumps into the drip tray than it would also mean heat tape on the drain of the tray and maybe even the tray itself. A properly set up and running HRV will make a lot of condensate in the winter time at least up here in the north.
The loop has always been dry. I have never seen water in the drain. Is that a problem?
The tech recommended heat tape on the drain line, but I don't know how much to credit his judgment since he thought terminating the intake inside the attic was fine.
Thanks for the link. I don't know how well that will fit. We have a very shallow overhang, so the soffits are quite small.
There would only be condensate in that line if the unit is running (is it?) and exchanging air through the core with a temp deference sufficient to exceed the dew point of the supply or exhaust air. If you are pulling air in via a warm/hot attic the core may actually be warming, not cooling, stale (moist air) from inside your home so you would not be seeing condensate. On a hot humid day, some condensate would also be generated as you cool that air over the core.
What make and model is that HRV? Have you pulled the filters and cleaned them?
It's a Honeywell VNT5150E 1000.
I cleaned the filters when we bought the house. The filters were filthy. I doubt the previous owner knew about the HRV since it wasn't listed on the disclosures, which mentioned only one air handler, not two. I just cleaned them again, but they were nearly clean since the system has been off for most of a year.
Ah, so an ERV, not an HRV. That drain will likely never see moisture in your setup. A frozen core is quite unlikely in your climate zone (where a defrost cycle might result in some water in the drain) and moisture would be exchanged in the core normally…so no condensate to worry about.
Today, I had the ductwork cleaned. The HVAC tech switched the intake and exhaust to correct the original installation that placed the exhaust closer to the air handler than the intake. The immediate result was a dump of dust since the direction of air flow was reversed. What had been the return was now the supply.
The duct cleaners found black spots in the air handler located in the unconditioned attic. He said the problem was worse with heat pumps than gas heat.
Going forward, I assume the condensation problem will be reduced by insulated the air handler while relocating the ERV intake to the soffits. But, I would appreciate confirmation.
If the air handler is going to be insulated, will the manner of installation matter? One recommendation was an insulated enclosure over the air handler. The alternative was duct wrap or foil-faced rigid insulation.
@bsawers-
How old is your house? How tight or leaky is it? Have you done a blower door test.
Do you even need a ERV at this time?
The house was built in 1955 with a gut reno in 2014 after foreclosure and fire. I had a blower door test done and the recommendation was that the house would benefit from an ERV, especially if I did any of the air sealing or insulation proposed. If I understood the blower door test results, the house wasn't sealed so tightly that an ERV was strictly necessary, but it was within the range of benefiting.
As a separate motivation, I lived in a house with Lunos and it was the best smelling house I have ever lived in despite poor outside air quality (diesel and woodsmoke). When first entering this current house, I often notice a smell, not terrible, but clearly not fresh.