David,

Have you look into power requirement for the electrical on demand water heater? It could be in excess of 100amps to get a 50F rise on 4gpm. That could require some major electrical upgrades. We installed a Rheem HPWH and have been very happy with the capacity and energy usage.

David,

Is there any reason why you wouldn’t be exploring the installation of inverter driven mini-split system(s)? It seems that you want to have additional stand-alone filtration in the home. The mini-split would benefit from this.

Mike

History:
In Tulsa OK — hot summers and a lot of humidity, cats and a dog in the house. Two people one working from home permanently.
Allergy problems of residents – lots of pollen/dust in Tulsa and the cats aren’t helping but they are too cute to rehome.
Inherited home 1600 sq ft — with an AC that was oversized because they wanted to convert the garage.
Vents under the house were leaky and even had holes.

Had some of the under home (crawlspace) feeds replaced
Sealed off the vents to and from the garage and then added another return in the house (next to the original) and added two overhead feeds to the two front rooms — because the contractor said otherwise the pressures would be too much.
Have a great collection of air filters in most rooms of the house
Have a small dehumidifier which works great (integrated pump) set at 55% and the air is set to dehumidify if it gets above 65%.
Added ecobee thermostat and sensors.
After the above — average bill dropped from $130 to around $100 even with added load of working from home.

I’m currently wondering if there is some reasonable way to get a better balanced system. The front rooms are important during the day and the back bedroom at night but its a small home and not zoned.

I have a Clean Comfort AE14-1620-51 which turns out is damaged but bought “new” at a yard sale rather cheaply. The neighbor and I are deciding how to reasonably deal with him forgetting to manage the damage to a replaceable unit. All together the unit is going to be about $200 + install costs.

The AC is a Trane, oversized (or so I’m told — before my time) and at least 10 years old.

My questions devolve to the following:

1. Clean Comfort air filter (yes/no) — or another brand?
2. Whole home dehumidifier? (yes/no) — SantaFe and which one?
3. There are times when the outside air is cooler than inside due to the Sun going down during the summer — opening windows is difficult to really vent and I’m wondering if we can get a system that will vent in using the AC ducts and just do it automatically.
4. AC replacement? I assume we are going to need to replace it. Should we go with a heat pump and a recommendation?

Financially, I want to tune the house for efficiency and comfort with as much “set and forget” as possible. Upfront costs are not a constraint as long as the return on investment pencils out.

Finally, not sure if it matters much but I’m getting solar for the roof, the solar will be more than our usage by design (EV in our future probably) and I happen to work for an installer. So, we are also looking to replace the gas water heater with an electric on-demand.

Allison,

Thanks for the article link. I think I have a plan. I’ll run a separate ERV duct up the AC supply duct just under the register. That way there should be very little effect when both systems operate. I’ll use a cape type BD damper on the ERV duct so that conditioned air doesn’t run backwards into the ERV when its not running. The dehumidifier will just operate in the basement for now to see if it will take care of the whole house before I invest in the whole house unit. Until I’m thinking about taking the dehumidifier discharge to the HPWH intake and then taking the HPWH discharge and dumping it through the floor below the refrigerator (then I’ll just need to synchronize them for simultaneous operation).

framistat, I focused on different types of ventilation systems here. There are many design details to address to have a ventilation system that functions well. Your problem with the intake is one. Other commenters have raised issues about ducting and where the RH readings are taken.

That’s unfortunate about your trouble with the Ultra-Aire 70H. I wonder why yours are failing so frequently. What have their warranty folks said about it?

I’ve also experienced leaking refrigerant in 70H units. Three in a row have failed. While the company has been honoring the warranty, it’s expensive to replace the unit every couple of years, even more expensive to have it recharged.

While considering alternatives, the current 70H is functioning only as a fresh air provider, with a separate dehumidifier operating in the basement. Being in upstate NY nearish Buffalo, humidity is high and fluctuates wildly.

Yeah, it can be tricky to put two positive pressure ducts together. Instead of a 90° tee, sending the dehu supply air into the AHU supply through a 45° takeoff so the air enters in the direction of the flow does work.

Ken Gehring of Therma-Stor, the manufacturer of Santa Fe/Ultra dehumidifiers, gave a talk at Building Science Summer Camp in 2016 on the reasoning behind dumping into the supply. You can download his slides here:

Lazy Air Conditioning, by Ken Gehring (pdf)

Your point about the venting dehu pulling both from its (re-circulating) return and its outside air-supply and therefore doing substantial mixing make sense. The 98H (just as an example) has a much larger return (10″ duct, I think) than the outside supply (6″ duct, I think), so I guess one is only seeing something in the realm of 40% outside air (6/16). Perhaps that was mostly a perception of feeling that the supply air during venting was quite humid 🙂

I know that there is some discussion on the location of the dehu supply when integrating with the AC ducting. FWIW, I discussed supply vs return mounting with my contractor and he was dead set against “supply to supply” on the basis that they’d had trouble with the pressure from the big AC blower outcompeting the blower on the dehu and meaning that the back-flow damper wouldn’t open fully, meaning less dehu air (aka higher static pressure in the dehu ducting) and whistling noises. Others don’t seem to have this issue (Corbin at Home Performance Channel tested and was satisfied that wouldn’t be a problem in his install). Just mentioning it because it doesn’t seem to come up in most discussions. Anyway, that’s how we ended up with a dehu supply to AC return configuration. We do appreciate not noticing the heated air from the dehu at all (we previously had a dedicated ducting system just for the dehu and even with careful placement the heated air was quite noticeable). We love having the dehu.