Furnace / HVAC in older homes

[sdho]

I know a lot of people have older single-family homes here.

Recently purchased a 1950 house that, for whatever unfortunate reason, was built with a gravity furnace (already kind of a dated technology then). The furnace is original to the house, is half rusted out, contains asbestos, and costs a fortune to run. And because the basement and attic were finished later, it doesn't serve half the house -- those areas are heated by yet-more-expensive electric baseboard.

Looking at replacing the whole shoot and match with a new forced air furnace and AC. Looking at about $16,000 for the new setup, plus $1,500 for the asbestos removal. (Got bids from 3 companies, all in the same range)

Anyone done this in an older house? Was it worth it? Experience with alternatives like heat pumps/split systems?

[Mikey]

Not sure on the gravity furnace upgrade part, but just swapping out our 1950's forced air furnace and adding AC ran close to $7500 twelve years ago, and that was with me personally running the ductwork to the second floor and basement ahead of time. I can tell you the electric and gas bills in the winter dropped over $100 a month each.

Try to spring for a dual stage or modulating furnace with a matching two-stage thermostat. They run at a lower BTU most of the time, taming down the "too hot - too cold" cycle, but have the umph to kick into high gear when you want really increase the temp, like right when you wake up. The two stage thermostat (with matching wiring) is key, otherwise the furnace will run in low gear for 10 minutes, then automatically kick into high gear, even if you don't really want it to

[sdho]

Thanks for advice. The HVAC guy also told me about the two-stage being advantageous, especially for older house with not-ideal register locations. Was planning to go for that (but was a little unsure if it was worth it or just another way to get the project cost up!). That total package costs includes the OEM thermostat for the two-stage furnace.

Right now peak utility bills are $250/mo for gas, $300/mo for electricity -- obviously other things playing into those costs, but the heating needs are clearly what cause the costs to spike seasonally. Efficiency gain for central AC would probably be more of a wash, but I'd have the whole house covered, rather than being 65 in one room and 90 in another. Great to hear that even going to new forced air made a good difference.

Was it worth the fuss to cover the upstairs and basement? Did you also have baseboard before?

[Mikey]

We did have baseboards upstairs (the house was actually from 1900 and had been converted into a up/down duplex in the fifties, so the upstairs was separate until the owner before us re-combined them). Depending on how much the ductwork costs, it's probably worth knocking your electric bill in half in the winter. For us, having our bedroom on the second floor connected to the central air was VERY important - it got nasty-hot up there and our window unit was running almost constantly when it hit 85 or more. Assuming you have a 1-1/2 story post-war house, the ductwork could make the second floor more usable.

I didn't originally put ducts in the basement - it was only half finished and there was enough heat radiating out of the ductwork from the old furnace to heat it almost too well. Dropping from a 1950's 100,000 BTU to a modern 40,000 / 60,000 BTU furnace cooled things down, so I eventually added in a few ducts down there

[mplsjaromir]

Two recommendations.

Unless you are getting a Heat Pump system don't bother with a high SEER system. There are not enough cooling hours here to make it worthwhile.

Multistage heating only makes sense if you have zoning. A new furnace with an EC motor that can run low speed constant fan will keep mix the air well enough. No furnace will fix bad duct work.

[Anondson]

A new furnace with an EC motor that can run low speed constant fan will keep mix the air well enough. No furnace will fix bad duct work.

I feel like I can confirm this. Our post-war 1 1/2 story’s upper floor had always been hot in summer and cool in winter. We needed to install a third supply to our upstairs. With closed cell insulation later, our second floor finally is the same temps as the rest of the house.

[sdho]

Multistage heating only makes sense if you have zoning. A new furnace with an EC motor that can run low speed constant fan will keep mix the air well enough. No furnace will fix bad duct work.

Surprised to hear this, both given Mikey's experience and other people I've talked to who have done the two-stage. The high-SEER thing was less for efficiency, more for getting the two-stage. (which was not available on less-efficient furnace)

Have you installed this in your own place?

I feel like I can confirm this. Our post-war 1 1/2 story’s upper floor had always been hot in summer and cool in winter. We needed to install a third supply to our upstairs. With closed cell insulation later, our second floor finally is the same temps as the rest of the house.

Oof. My main issue with additional registers upstairs is the disruption to main floor to make space for them. Even two + one return is kind of an imposition. (first HVAC guy actually recommended just a single supply, which seemed dubious) Do you have multi-stage or single-stage?

[sdho]

I may as well be specific here. Total cost I am looking at is $18,500.

$1,500 is for asbestos removal of existing furnace
$17,000 is for new furnace (96% furnace, 17-SEER AC), duct work, and new water heater. They recommended switching out the existing water heater for a side-venting model so I could abandon existing chimney and use it for ductwork to second floor.

I would save $3,500 if I went to single-stage 92% furnace and 13 SEER AC. I would also get $1000 less in rebates from manufacturer and energy companies.

So, when all is said and done, is it worth $2,500 to get to 96%/17-SEER and 2-stage? I feel pretty strongly leaning toward "yes"

[mplsjaromir]

The house I bought had a two stage furnace installed and just runs on second stage, first stage never hooked up. Typical to 80% of installations.

If you like the furnace, coil and condenser match up you should definitely go for it. I just wouldn't expect to notice much difference from a multistage furnace in your particular situation. Sounds like you will have relatively clean slate so there is no reason to get it as good as possible at one time.

[sdho]

Update: got the furnace as described. Works *great* for first floor and basement, but AC barely makes a dent upstairs. Which, I guess I knew was a likely risk, but a little disappointing. One thing that I think is making the problem even worse is that they installed a self-adjusting "Cor" thermostat, that adjusts the fan speed, but doesn't allow the user to control it. So the main-floor thermostat gets to a content temperature and sets the fan to low, and I have no ability to override it and set fan to a high speed like I could with a conventional furnace.

Probably just going to subsidize the upstairs with a window AC this year. Maybe a ductless unit next year? The roof is fully exposed to sun and it's just 6" of fiberglass batt insulation, so I'm not sure how much of a difference even a zoning retrofit would make. I guess I wish I'd realized that before spending the money to run ducts upstairs.

[seanrichardryan]

Sounds like a balancing issue. We used to close basement and first floor vents in summer to send all ac up to 2nd.

[sdho]

Tried that one. There are dampers by the plenum trunk for most, and I have adjusted everything downstairs way down. There is one vent without a damper or an adjustable register... I will get a new register for that and try shutting that down too. HVAC company is sending out a tech tomorrow to see if there's anything I can do about fan speed.

[sdho]

Alright, they disabled my low circulating speed, so it's just medium or high now, and shut off even more to force more air upstairs. Eager for another hot day to try it out.

[mattaudio]

Sounds familiar. Things that have helped:

1. Being able to run my furnace fan on low 24/7 regardless of heating/cooling cycle. Having this low current of air seems to balance things out really well.

2. Better attic insulation! If anyone has a half story and is getting a new roof, spend a little extra money to bump up beyond your existing roof decking. I added 2" of XPS foam (removes the thermal bridging of joists too), added 2x4 stringers to create a continuous soffit and ridge vent, then new roof deck and roof. Of course get a structural engineer to sign off on it, and you'll need to adjust your fascia. But so worth it!

3. Seasonally shutting off different registers.

[sdho]

Insulation is definitely something I want to look at in the long term. I didn't actually realize you could add more insulation to the outside surface. But right now, the roof is only 8 years old, and I really love the interior finish, so I wouldn't want to wreck that to do spray foam (even if cost were no object). I expect the "trigger" would either be a new roof or a more major reconfiguration of the space that requires changes to roofline/ceiling.

Today was great -- not very hot, but sun was full exposure and things kept up fine. Looks like we'll have some hot ones to give it a truer test this weekend.

[kiliff75]

We have a 1 1/2 story bungalow that gets full sunlight throughout the day, and it gets quite hot in the converted attic. We are getting a new metal roof that is less reflective (and stores less heat than an asphalt roof) with spray foam insulation under the roof deck...we'll see shortly if that makes the upper-level more comfortable!