HVAC Upgrade for Old House
Hey there, everyone.
I’m a builder in NE Pennsylvania living in an 1860s Victorian and looking to upgrade the heating and cooling.
BACKGROUND: The house is a 3000 sq/ft Victorian with 10’ ceilings. The previous owner had cellulose blown into the attic and walls. On the south facing side of the home (lots of exposure to sun and wind) I replaced all the siding, insulated with rockwool, and installed Zip system for an air barrier. All other exterior walls appear to be clapboard applied directly to the studs, but from what I have seen there is little rot on the home. We had the exterior painted and did a lot of caulking and sealing around the clapboard.
The house currently uses an oil run boiler with steam radiators on the first floor and a mix of radiators and electric base on the second floor. The house is relatively comfortable in the winter (I still have some air sealing work to go), but I’d like to move to something more efficient and healthy.
OPTION 1: Convert steam radiators on first floor to hydronic run off a Navian propane boiler in the basement. This requires little damage on the first floor.
On the second floor I am considering a ducted mini split or heat pump air handler built into a bedroom closet. The attic is undconditioned and I would prefer to keep it this way. We could run the ducts up into the ceiling joists and have them buried in the existing cellulose.
option 2: ducted split or heat pump air handler in basement to run floor mounted registers on 1st floor. The 2nd floor would have a second split or handler system.
It is important to me that we do not run line sets all over the exterior, as the home is historical. This rules out the wall units. The interior is also in good shape, so I’d like to avoid demoing the original horse hair plaster as much as possible.
My biggest concern is whether or not the heat pumps could keep up with heating such a big, drafty home. I believe they could handle the second floor, as we hardly run any heat up here now, but the first floor calls for a lot of heat. Currently our oil bill is around $700-1000 every 6 weeks.
Any advice, equipment recommendations, and references to articles would be greatly appreciated. As a young remodeler/builder, I see this house as a long term experiment that I would like to represent my work ethos, so I want to make sure my decisions are well thought out.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Use this to determine the heat loss:
I think you're within heat pump range, but if not you have an existing boiler so just use that for the coldest days. Compared to a heat pump, all propane boilers are inefficient and don't provide AC. 1 heat pump per floor will probably be more convenient and resilient.
That is a huge house. The oil usage is not that bad for a house that size. Air seal and insulate as much as is practical. How are the windows? All of your ideas are very expensive. Spend you money on oil, enjoy the house, and move on when it gets to be too much. No matter what you do, it will always be a big old house with a substantial heating bill.
I should add that the boiler is old.
Currently, we have mediocre storms that I am working on updating. I don't think that the money spent on replacement windows would ever be worth it, and the original windows are beautiful.
There is a good chance that this is a house we would like to keep for a very long time. Replacing the oil system is not only for lower monthly bills but for the sake of lowering our environmental impact.
I encourage you to read Jon Harrod's six-part series on the topic of replacing fossil-fuel heating with a ducted heat pump system (links to the full series appear at the bottom of the page).
Do NOT install a propane Navien combi boiler or boiler! Their track record on exhaust-leaking heat exchangers leaking is abysmal, and propane pricing is highly volatile (not to mention the CO2 and PM2 emissions from burning propane.)
It is likely possible to efficiently heat the first floor just fine with a monobloc style air to water heat pumps using a mixture of radiant floor & /or panel rads. Only a room by room heat load analysis would tell you for sure. If you can keep the water temp requirements below 120F (under 110F is better) at design temp hydronic heat pumps can be great!
>"Currently, we have mediocre storms that I am working on updating. I don't think that the money spent on replacement windows would ever be worth it, and the original windows are beautiful."
That's right! A tight low-E storm window over a reasonably tight wood sashed double-hung is roughly comparable to the performance of a code-min replacement window, and is easier/cheaper to install.
Low-E glazing is key- even though it increases the upfront cost, the "payback" on energy cost is about half that of clear-glass storm windows, which should be well under 10 years (simple payback) if heating with propane & /or electricity, under 3 years if heating with resistance electric. The tightest storms in the industry WAS Harvey's Tru Channel, which comes with a hard coat low-E glazing option, but I don't seem to be able to find them on their current website(?). (Hopefully they are still being made!) Larson's low-E storms sold through box stores aren't bad, and have improved over the past decade. There are others.
While you still have access to the heating season oil fill up dates and amounts, run the fuel use-based heat load calculation (that Paul linked to in the original response), utilizing weather data from a nearby weatherstation. The methodology is explained in detail here:
That will only give you a block load for the whole house, but consider it an upper bound, since the old boiler probably isn't hitting it's nameplate efficiency on an as-used basis. That should give you greater confidence on your room by room load numbers using a Manual-J tool.
For sizing heat pumps I strongly recommend using the BuildBetterNW freebie tool over other free online load tools. It's fairly easy to use (even for newies), and uses default U-factors that are much less likely to overshoot reality.
(You have to sign up to gain access, but it's all free.)
That tool was created by a consortium of utilities as a means of combating oversizing problems that are rife in the HVAC contracting world. Oversizing a hot air gas furnace by 3x doesn't have much impact on operating cost or efficiency (only comfort), but oversizing a heat pump can be financial & comfort disaster.
Thank you for the thorough response. I am bringing in an energy consultant to do a manual j, thermal imaging, and probably a blower door test (that will be painful to witness).
I have been bouncing around different ideas and I feel that an air to water heat pump is likely out of my price range. I’m hoping that eventually the air to water units come down in price to something more attainable.
With that being said, I’ve been curious if it would be reasonable to convert my radiators from steam to water and use an electric boiler to run them? I would combine this with ductless splits and only run the boiler when necessary. I’ve heard they can be expensive to run, but I can’t imagine it being more than my current oil bills.
Thanks for your response.
I am now in the process of installing two ducted heat pump systems based on my sizing calculations on betterbuiltNW.
We are going with a 36k btu Mitsubishi condenser and a 3 ton Goodman air handler for the second floor and a 48k btu and 4 ton handler for downstairs. I’m working on building a closet into a guest room that will house the air handler and plenum on the second floor and then running ducts in the attic below our cellulose. The 1st floor system will run in the basement.
We also ordered new storms for the entire house. Once those are in we will likely have a blower door test done (ignorance is bliss, but we should probably know what is going on with air leakage).
Our next goals will be to spray foam one part of our roof (where an addition was added in the 40s and insulate the basement ceiling to prevent heat loss into the basement.
Long term, we are looking to put a PV array on the house as we have a ton of southern exposure.
As a young builder/remodeler, I’m determined to focus on carbon emissions and I figure my own house is a great starting point. Hopefully the bills will be less too since we were averaging $450 in heating if you average it over 12 months.