Options for good IAQ in older home-first install of HVAC
I'm amazed at the depth of information and insight here. I'm hoping y'all can give me some advice.
My wife and I are buying our first house, in Washington DC. It's a 1918 American Foursquare (Craftsman, Arts & Crafts). About 850 square feet on each of the first and second floors, maybe 400 square feet on the third floor, and then a 800 square foot basement. The basement flooded in the past, but out inspector assures us that regrading so the land slopes away from the house, a swale, and reworking the gutters will take care of that.
We're installing hvac for the first time. Our general contractor recommends a high-velocity AC system (along with the existing radiator heat), which makes sense to us. He's saying that either we could do a dual zone, with the basement and first floor on one zone, and the 2d and 3rd floors on the other, or a single zone for he 1st, 2d and 3rd floors.
If you have any thoughts on high-velocity AC generally, or the one zone versus two zone, I'd appreciate hearing them, but that's not the main reason I'm writing.
Because we're concerned about moisture in the basement, our contractor was making noises about installing a heat recovery ventilation system. Looking at that, it basically looks like a heat exchanger to me, which seems more likely to add maintenance hassles than to significantly reduce energy costs (especially after cost of installationg). What do you think? Any thoughts on HRV generally?
More importantly, after looking at what I've seen on hvac-talk, what makes sense to me is to install an whole-house dehumidifier, acting on both fresh air intake, and on the return air, so that we can keep RH below 50%. Also, that way, we can run the dehumidifier when the weather's right and not run the AC, which should save on energy costs. Any thoughts on a whole-house dehumidifier versus an HRV, or a whole-house dehumidifier in addition to an HRV?
Also, do you know which whole house humidifiers use a standard filter, as opposed to a custom one?
Finally, can you recommend any good AC contractors in the Washington, DC area? I don't know who our general contract works with, and I'd like to have some options.
Thank you, very much.
Very perceptive! During cold windy winter weather, your home will get enough natural fresh air ventilation. Yet during calm moderate temperatures, you will benefit from fresh air ventilation. Using a whole house ventilating dehumidifier is the most practical method of being able to providing upto merv 14 air filtering for both the fresh air and house air. This will also assure <50%RH throughout the home during damp cool weather. This requires a return from the open part of the house and a 6" fresh air return to the WH dehu. The dehu supplies goes to the three living areas of the homes and a small supply to the basement. Consider the possible addition of humidifier to dehu loop for winter humidification if needed. The fresh air ventilation should be provided when the home is occupied and the weather moderate.
Originally Posted by vorkosigan1
Regarding the a/c, high pressure is ok. Avoid any ducts in an unheated attic space which can have winter condensation problems.
I suggest that you consider the Ultra-Aire 105H is the optimum WHV dehumidifier. They are one of the sponors of this web site.
Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
Use +Merv 10 air filter. -Don't forget the "Golden Rule"
1. Get a second house inspector.
2. Your basement will get some water infiltration at some point, and it will be cold and humid all the time. I strongly suggest discharging most or all of the output of the dehu in the basement if you want to use it at all. I know it's not TB's favorite configuration but I've tried various ones, and this has worked best for my house. It has evened out the temperatures on the various floors, preventing mold and discouraging insects in the basement.
3. An ERV still requires a dehu, just a smaller one. It's about the same cost of ownership (including operating costs) to get an ERV + med. efficiency dehu, or a large high efficiency dehu. The ERV only helps on the dehumidification costs of fresh air, and doesn't help dehumidify a basement.
4. An HRV doesn't help you with humidity control.
5. Basement and first floor have extremely different conditioning needs. I suggest not putting them in the same zone unless you follow my suggestion to discharge the dehu in the basement.
as already mentioned by others, the HRV unit is not designed to take out the humidity in basement. plus you also need to somehow get the makeup air from your house above for heat recovery but unlike normally the pre-treated outside air will go back into the same space, this pre-treated outside air is to be supplied to basement leaving the house in a relative negative pressure. depends on how big the air flow you're talking about, this will increase the infiltration rate to your room above basement which you do not what.
i'd have thought a standalone dehum system for basement or at least an exhaust ventilation with makup air to create cross flow would be more suitable.
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