View Full Version : HVAC for Historical Home
06-15-2007, 06:02 PM
I just closed today on an old house in northwest Ohio. I know as much about HVAC as the Government knows about saving money.
The house has a very old forced air furnace with ductwork only to the lower level. The furnace is on it's last leg. (old, rusty, poor ductwork, etc.)
We built in the home loan to get a new system. We've had two estimates but neither so far has really impressed us. I'd first like to know what kind of questions I should be asking, as far as the basics. I've done some reading on the internet but I still have no idea what I'm talking about.
Here are the basics on the home. It was built in 1866. It's triple brick walls and it has insulation which appears recent in the attic. There's no ductwork in the upstairs at all. This is what I was considering.
I wanted to split the system up. Put a furnace & A/C for the upstairs and one for the downstairs. That way we could limit what we do upstairs during the day where the bedrooms are located.
I wanted at least a 2 stage system, variable speed, and I would like a dual fuel system. One of those heat pumps that will kick over to propane when it gets too cold.
What could I do to save some money that wouldn't sacrafice quality, what kind of questions should I ask, and what other advice can you give? I know I'd like the whole house humidifier for Ohio winters. What about an air quality unit? Am I on the right track here???
Thanks for any responses.
06-16-2007, 10:46 AM
I too have an old home (built 1889), but not necessarily historic. When I purchased the home two years ago I assumed that since it had been renovated that it was in good shape with regards to the comfort systems and the cost to keep the home heated and cooled. Ha!!
After the first winter I knew I needed to figure out where all my energy was going. Old homes are normally very, very loose and thus there is a lot of air infiltration. In the winter that means lots of cold air and during the summer lots of moist air coming into the home. Insulation alone does not resolve infiltration.
After much research I have decided on and started having the worst areas re-insulated with spray foam insulation. This resolves three things all in one: insulates, stops infiltration (at least where the foam is applied), and provides a vapor barrier. I have had the attic done (cathedralized) and next I will have the crawl space closed off and sealed with spray foam (plus new sealed ground cover vapor barrier and de-humidifier). After this has been done I will then have a blower door test done that will identify additional gross contributors to infiltration and heat loss/gain.
The systems in my home are an oil fired hot air furnace with a net output of 96,000 BTU on the first floor and a 3 ton (36,000 BTU) heat pump on the second floor. Also, to cool the first floor, there is a 2.5 ton air conditioner.
I have run a load calculation (software downloaded from this site) to determine what impact the changes I am instituting will have on energy consumption. The before and after is rather significant. Instead of the 5.5 tons of cooling that I currently have I will need 3.5 tons and the heat requirement is about 68,000 BTUs – substantially less than the current heating capacity of the 96k furnace plus the 3 ton heat pump. Therefore, all my systems will be replaced.
I have also done a lot of research on the efficiency of different systems. Ground source geo-thermal heat pumps are near the top but way out of range for my budget. Propane provides only about 92,000 BTU’s per gallon while fuel oil provides about 140,000. In my area, the cost per gallon of propane and fuel oil is about the same so the cost per BTU is much less for fuel oil than propane.
On a duel fuel setup where a heat pump is your primary heat source it will have to be stopped at about 35* and the secondary heat source will then take over the heating needs. I wasn’t impressed with this setup since heat pumps still provide a fair amount of heat at 35* and even down to single digit outdoor temps can provide about one third of the nominal amount (i.e.: a 3 Ton stills puts out about 12,000 - 13,000BTU’s at 7*) and at a COP of about 2.0 (i.e.: putting out twice as many BTU’s as it is consuming in BTU’s). This is still fairly efficient. Of course, that is influenced by the cost of electricity.
So the route I am taking is to use oil as a supplemental heat source when the heat pump can’t carry the heating load. But, instead of the using a force air furnace that would require a hard switch over from the heat pump, I will use a hot water coil installed in the duct to supplement the heat pump - not replace it as the heat provider, when the outdoor temps drop below 35*. The water will be heated with a boiler (lots of improvements in this area with electronic controls and such) and provide for our domestic hot water needs and supplement the heat pumps when that is needed. The water temp will automatically go up as the outdoor temps drop and thus I won’t be keeping water hot when it is not needed.
With the higher BTU output of oil, the efficiency of a boiler system combined with a hot water coil, and the fact that it can be used to “supplement” the heat pump(s), I believe it is a cost effective way of heating our old home. During the summer the two heat pumps (both will be multi-staged with variable speed blower and comprehensive control systems) will provide for cooling needs. I may also install a whole house de-humidifier.
There are a number of ways to retrofit equipment in an old home. That is best determined by contractors on site that can see and work within the limitations your home requires.
I hope this helps.
You are on the right track,two stage,variable speed ,IAQ,etc..
Two stories really needs two systems or a Zoning system.If there is space to run ducts from the first floor to the second,zoning would be my choice.
You need a Contractor that will do ALL the calculations/engineering that is required.
Manuals J,S,D and T, all from www.acca.org
That a look on that site for QI,Quality Installation,free download ,it will tell you what a QI should include!
Take a look at Carrier's Infinity,dual fuel,very slick system.
06-16-2007, 06:10 PM
Ditto Dash's comments. Please also note that Bryant products have the same "Hybrid Heat" as the Carrier products. Same company afterall. Having said that however, almost all companies have some sort of dual fuel controls. Also, the 92,000 and 140,000 Btu contents of the two fuels are gross amounts. You need to multiply by some efficiency constant to get the actual output from the fuel and the furnace or boiler might also arrive at a different output.
Geothermal should not necessarily be ruled out. If you have to put in a fully ducted system and are thinking of high end equipment, I think you might be surprised to learn that the costs of the ducts and equipment usually aren't that much different for geo. The only difference is the earth coupling. In our state, Massachusetts, there are loans available a anywhere from 0% to 3% with a 7-year term for geo installs. You can also get those loans for other high efficiencye equipment.
06-16-2007, 10:16 PM
The nicest sytems I've helped put in Historic homes were chilled water with fan coils in the ceilings of closets. Up front this is expensive, but since unused space is in set back saving can be great. For a DX sytem you could put the upstairs unit in the attic. Put two over flow pans under the unit, first one will drip where you will easily notice it, second one will shut the unit down. Don't use a float on this one, use water detection probes. They have wood look grills that are made of fibreglass, also moulding that goes up next to the ceiling that is a hiddened diffuser.
06-16-2007, 10:20 PM
utility closet on first floor --
a) large enuf for air handler w/ furn
b) chase from bsmt to 1st & to 2nd --
drop ceiling in halls for ductwork to distribute air
insulate attic first!!
fill gaps around window frames & doors
add storm windows inside at sides which must be kept historic --
storms protect main window, help with infiltration, add extra layer against robbers --
consider furring & insulating inside walls on 2nd -- at least main bdrm & bath
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