Ventilation/ductwork retrofit considerations
Recommendations on adding provisions for ventilation to an old house? As of right now, we have only windows and a chimney. No ductwork, registers, or transfer grates.
Within the next 18 months, we should have:
– added kitchen/bathroom exhaust fans
– replaced 2 unvented gas heaters with several ductless mini-splits
– wrapped the house (walls/roof) with a self-adhered WRB
– encapsulated/air-sealed the basement, ala Joe Lstiburek
(https://www.buildingscience.com/documents/insights/bsi-041-rubble-foundations)
Assuming that we’ll want an HRV/ERV, it will presumably require ductwork to support it. At ~1000 sq ft on the first floor, and ~700 sq feet on the second floor, the house is compact. The to-be-encapsulated basement will be available for mechanicals. The mini-attic could also be available, if we air-seal and insulate over the roof deck. Suggestions welcome!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Kitchen and bath fans could be useful if anyone would ever turn them on.
I like the mini split part of your plan especially if you are cutting off the gas main and going 100% electric.
I do not see doing the WRB unless the old siding has failed to the point that it must be replaced. I see no way you will ever recover the costs in energy savings without adding insulation.
Do you have a rubble stone foundation?
Have you attached the low hanging fruit, like air sealing the ceiling and attic insulation?
In my opinion short of gutting the house to the studs and replacing the windows and doors, there is little chance that the house will be tight enough to require an EVR. You can add it if you get a blower door test under 1 ACH 50 or your winter time indoor humidity is somehow over 55%.
Hi Walta,
We're still in the process of purchasing the house, so absolutely nothing has been done yet. My full description of the task at hand: https://www.greenbuildingadvisor.com/question/old-home-renovation-order-of-operations
As for insulation, there's almost nothing in the walls, and the attic is completely un-insulated except for dust and bat droppings. So the plan is to air-seal/insulate/re-clad in one swoop. As you gather, it's on a rubble/fieldstone foundation with a dirt floor. Site drainage is quite good, but we'll all be happier when the basement has been encapsulated and the house has been WRB-wrapped.
ERV/HRV guidance noted. Any recommendations for managing within-the-house circulation of air? (especially to/from the bedrooms) Even if it's not necessary, I guess I'd also feel better designing in a chase for future ductwork (should that blower door test ever come in under 1 ACH 50). Thanks!
Even if you are just doing basic renovation to the house without much attention to air sealing, the chances are the house will be more than tight enough to need mechanical ventillation. Since the air leaks in the house can be anywhere, they will not necessarly be where you want them (ie bedrooms), so mechanical ventillation is a good idea. If you are in cold enough climate and HRV/ERV might be worth the cost.
If your area has high humidity and you need the mini splits for cooling, your best bet is to have at least one ducted mini split to feed the bedrooms. Wall mounts in hallways can work but you need to leave the doors open otherwise the bedroom temperature goes up a fair bit. Whatever you do, make sure to keep all your ductwork (both heat/cool and ventillation) out of any unconditioned space.
Generally for a two story with mostly open main floor, you can have a single central wall mount unit on the main floor and a ducted unit for upstairs. These should be on their own outdoor units (you don't want a multi split).
Depending on your final insulation and window sizes, you might need a bit of supplemental heat around the perimeter of the main floor. This can be a bit of electric floor heat or baseboard/panel heaters.
I just wanted to second the likely need for mechanical ventilation despite it being a leaky old house.
The leaky old house that I live in is 10ACH50, and the bedrooms regularly get in the 1400 (or higher) range without active ventilation. Other parts of the house do fine due to the aforementioned leafiness, but like Akos said, there’s not a great way to choose where those leaks are.
Agree with last few comments that you will need ventilation. I’m working on a very similar house as this. 1600 sq ft 1.5 level with only one bath, no duct work . I gutted the oil, gas and went with manual j/s guided ductless. We essentially had no room for ducts but I think this was also my lack of knowledge and poor hvac company experiences. After measuring CO2 levels with bedrooms >2k I purchased a CERV2 and doing the duct work myself. Finding a chase will be the most challenging part. Ducting a mini split to the bedrooms will be the ideal situation and I wish I had done that. Fresh air could be tied into this duct work or have separate duct work. Also I would consider a whole home dehumidifier like aprilaire/Santa Fe which I’ve also added and has made a huge difference in our comfort since the high SEER newer mini splits are awful at dehumidying.
I’d be interested to hear about the WRB and whether you’d do this yourself.