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1870s rowhouse rehab energy efficiency – radiators and radiant heat?

humbleadobe | Posted in Energy Efficiency and Durability on

I’m looking for feedback on heating and cooling (and energy efficiency) for a large, three story brick, italianate 1870’s row house (with low-sloping flat roof) – it’s attached to the neighboring brick house on the south, with a few feet between houses with the neighbor to the north). This is a big (4000 sq. ft), brick, main street structure with massive walls and many average sized (15′ x 15′) rooms that can’t be opened-up too much because of the existing structure. The building is basically already set up to have three studio apartments in the front of the building and a separate 3 story “townhouse” for the rear of the building (includes basement, 1st, 2nd at rear) – with side-by-side, central staircases dividing a long row house front/ back.

My basic heating / cooling plan (after gutting down to existing structure and leaving most of the walls) is to use

-an efficient natural gas boiler (suggestions?)
-PEX tubing going out to each individual radiator to adjust heat ?(suggestions?)
– refurbished cast iron hot water radiators (definitely)
– in-floor radiant heat throughout the basement floor (probably)

SHOULD I run the basement hydronic radiant heat (in concrete) off the same natural gas boiler heating the cast iron radiators? HOW?

Should I use any specific type of insulation or barrier in the sub-floor spaces? Should I use new-insulation over every original exterior wall and re-drywall over? I would be replacing the roof and having some skylights, cool roof of some type, and new insulation for the crawl spaces (suggestions on insulation?) I would be rehabbing the existing historic windows and adding simple storm windows

I would put on a minimal depth/ weight green roof and try to naturally ventilate above the existing stairwells with a basic solar chimney (to get natural ventilation and air movement as much as possible)

I would provide a central AC unit to each living area with an exposed air duct – (how should I design air output / intake?) The area gets hot and especially humid and stagnant and will not be appealing without air conditioning

I also need to replace the electric boxes (where it comes into the building) should I plan to re-wire the apartments that have modern wiring? (if it’s from the 70s?)

does this sound reasonable and cost-effective? I’m new at this – i realize most of the energy savings will come from window and door leaks, insulation, and not having an asphalt roof in full sun

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  1. GBA Editor
    Martin Holladay | | #1

    Humble Adobe,
    Any heating contractor who specializes in hydronic (hot water) heating systems should be able to advise you on your hydronic system.

    When it comes to insulation:

    1. Here is a link to an article that provides advice on basement wall insulation: How to Insulate a Basement Wall

    2. Here is a link to an article that provides advice on insulating brick walls in older buildings: Insulating Old Brick Buildings.

    3. Here is a link to an article that provides advice on insulating low-slope roofs: Insulating Low-Slope Residential Roofs.

  2. humbleadobe | | #2

    Thanks Martin; previous renovation added basic 2 x 4's and styrofoam type insulation on some of the long exterior wall - the brick is in decent shape, in Wheeling, WV near Pittsburgh (lots of wet, plenty of freeze / thaw) - the whole opportunity of the building is that the timber frame and brick has survived 150 years - ALSO - it's not that cold here and it's getting warmer every year so after reading that article - heating and drying the brick (and having it breathe) is way more valuable to me than insulation (which would also add lots of re-finishing costs I could avoid - as budget is a primary concern - gorgeous building in a place with very low real estate value).

  3. Expert Member
    Dana Dorsett | | #3

    Don't hand the project to a hydronic designer without having an aggressive Manual-J load calculation performed by a qualified third party, on the "after insulation & air sealing" condition of the building. Contractors tend to oversize the boilers (usually by quite a lot- even 3x oversizing is all too common), which cuts into both comfort and efficiency (or even the longevity of the boiler), as well as adding to the up-front cost. See:

    Refurbed high volume cast iron rads work great at low temperatures, and add significant thermal mass to the system which helps limit the short-cycling issues. This is particularly important if you are micro-zoning. Tweakable radiator thermostats can help adjust the room-by-room temperature balance, but aren't always adaptable to antiques. Sizing the equivalent direct radiation (EDR) proportionally to the room loads and going with fewer zones with more radiation is going to be cheaper and easier to implement (= harder to screw up) than micro zoning on a room-by-room basis.

    Depending on the load numbers you may be able to get there using a tank type hot water heater combi rather than a boiler. A tank type water heater is inherently self-buffering, which makes it nearly short-cycle proof in micro-zoned situations.

    Stagnant humid air is about ventilation, not air conditioning/cooling. A recirculating ducted ventilation system should be able to help distribute dry, conditioned air throughout the building with it's own (small) duct system, as well as delivering fresh outdoor air, which may relieve the need for ducted air-conditioning to every room. Combining air conditioning with ventilation is usually a bad compromise, since ventilation rates would then track to the duty-cycle of the AC, which is NOT what you want to do. Ventilation air is needed even when there is no heating or cooling load, and when the latent cooling load (humidity) is high or heating load is high it's better to lower, not increase the ventilation rates.

  4. humbleadobe | | #4

    Thanks Dana - the article is very helpful, If I could have a tank system, that might actually be brilliant - as the philosophy for the design is to heat a huge brick structure everywhere at a low level (also why I would put radiant heat over the whole basement - and to create a comfy garden level floor at the rear half of basement) I wasn't planning on micro-zoning so much, but I'm trying to avoid the common phenomenon I've seen in older buildings with radiators where one apartment is 10 degrees hotter/ colder - I would need a way to adjust the heat on a living space (3 one story units in the front of the building, 1 three story unit (potentially a half-open ceiling over the basement there) - so I guess I could save a lot of hassle by hooking up 2-3 radiators for each living space to the same feed. Stagnant humid air is about cultural norms and public perception among people that aren't architects - anybody who rents or buys the building in the future is going to want "central air" - I also like electric cars ;-) . Oh, I wasn't talking about air conditioning in every room - the whole idea is to take advantage of the high ceilings and historic design - but just as you say, I need some modern ventilation to list it - I'm talking about one exposed duct and one return per living space - not per room (but we're talking about 500 sq. foot studios in the front - the only thing is having separate units to divide utilities and maintain separate air zones (the building was divided into apartments like 100 years ago maybe so this is really about simplification and taking advantage of the structure as it is - no , no - I'm talking about natural ventilation over the 40ft. stairwells - which would work well in this building - BUT I would still need to have central air for the summer months because it's kind of gross and humid without it. Let me phrase the question this way - is there a good way to combine natural ventilation with a minimal ducted system - so that you could DEHUMIDIFY and COOL the air 5 degrees in the summer (because I'm already talking about a big brick building with a shade tree and a cool roof, and it's not going to get too hot anyway - AND (for american marketing and comfort reasons - I'm serious that I will still need to have central air conditioning or nobody in this area will be interested in my brilliant natural ventilation design other than me - strictly about cultural perception (and 5 degrees cooler and less humidity during the summer months - in which the humidity is thick, hazy air, smells from the ohio river (serious jungle humidity)

  5. humbleadobe | | #5

    Concerning cooling and efficient ventilation (taking advantage of being on a riverfront hillside with rear of building being tall and facing a shade tree and summer wind - as the builders did in 1870) I think I'm suggesting FAN ASSISTED natural ventilation (or a serious solar chimney design) - and, in the summer months - there would be some ability to turn the ventilation system to Air Conditioning within each of the four living spaces - and pay for air conditioning individually (so that the building is designed to stay ventilated and cool - but the option for central air exists for modern American cultural norms and dehumidification).

  6. humbleadobe | | #6

    the huge stairwells (which take up the entire center 15 x 20ft. space will easily stay cool - they aren't too warm as is with no windows open, no air, and a black tar roof overhead - but will also function as 40 ft. stack effect ventilation from the basement to the roof - which seems like it has so much potential to naturally ventilate it would be extremely worthwhile (also, going from garden level rear shade to hot urban full sun rooftop space - so it's already like a 20 degree temperature difference in general

  7. Expert Member
    Dana Dorsett | | #7

    The air volumes needed for cooling using a night time ventilation scheme are orders of magnitude higher than you would use for everyday ventilation. A "whole house fan" useful for nightime ventilation is typically several hundred to over 1000 cfm, whereas for normal continuous ventilation runs 10-25 cfm. Using the same system to do both doesn't work.

    In humid climates nighttime ventilation schemes don't work well- it can be useful for the sensible load (temperature) but is working against you on the latent load (humidity.) When the outdoor dew point is north of 60F, forget about it- it'll just make it sticky or clammy feeling- a lower temperature, but not higher comfort.

    A 500' studio can be air conditioned with a half-ton or 3/4 ton mini-split heat pump (or strictly cooling mini-split), but for a minimalist ducted more centralized system you may be able to do it with a 1 ton or 1.5 ton Fujitsu xxRLFCD modulating slim-ducted unit per floor. Sizing it for the actual load is still important, and getting the duct design right is critical for keeping all apartments cool without freezing some apartments, roasting some others. With tall rooms and three floors it will have to be zoned at least by floor to get any sort of temperature balance. So pay attention to the Manual-J for cooling loads too.

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