New gas furnace for big old house

[abcs]

Greetings, and thank you in advance for your assistance.

We own a pretty big 1901 "Princess Anne" (late Victorian) single family, about 3800 sq ft if you include the very unfinished basement, close to 3000 for the 3 living floors, high ceilings, lots of windows. We currently have a 10 year old, 148,500 BTU, 85% oil furnace. 10 years ago I myself ran a heat loss program, carefully measuring and entering every detail, and came up with 127,000.

We would like to replace our system with natural gas, which is already coming into the house for our water heater and cooktop only. We live in New England and heating with oil has become horrendously expensive. We would like, ideally, a highly efficient (at least 95%) direct vent, two stage, variable speed system.

Cost is NOT the issue. Two problems, for which I am requesting advice:

First of all, efficient gas furnaces simply do not come as big as oil furnaces. We have gotten several estimates, and nobody seems to know what to do about this. The alternatives seem to be either a 133,000 BTU single stage, non-variable-speed system, OR a 120,000 BTU variable speed 2 stage system, which appears to be as big as they come. Those who recommend the latter insist it will be big enough, due to high efficiency. I just don't know. Which would you do? Any alternatives? (I know there is also the possibility of twinning two smaller furnaces, but if I am not mistaken that precludes the variable speed option anyway - so might as well just get the 133,000 single stage - right?)

One reason I really want the variable speed motor is that I think it will heat my house more evenly. The upstairs never gets as warm as the first floor, which is where the thermostat is. The system comes on full speed, warms up the foyer and the thermostat turns off the system. I think variable speed would help.

Second problem, which wasn't mentioned by anyone until the 4th estimate: presently our furnace and water heater vent into the chimney. I am now told that removing the new direct-vent furnace from the chimney will necessitate either a new expensive chimney liner for the water heater, OR a new power-vented water heater (it may be a problem to find a good place to vent it). The water heater is very old and we don't mind replacing it, but I'm not sure what steps we have to take and why the first several contractors failed to mention this. (We have been told lining the chimney for a regular water heater will cost several hundred dollars - or several thousand!)

Thank you again for any guidance on these two issues.

[tipsrfine]

If cost is not an issue, why not look into putting some money into tightening up your home & improveing its insulation levels? Could be that you could get your heating load significantly reduced, and improve overall comfort.

[abcs]

If cost is not an issue, why not look into putting some money into tightening up your home & improveing its insulation levels? Could be that you could get your heating load significantly reduced, and improve overall comfort.

Thanks, we've done quite a bit of weatherization - had an audit and followed through on most of the recommendations. By the way, let me clarify - I said "cost is not THE issue," not "cost is not AN issue." We are not wealthy. But oil is so expensive that we expect to recoup the cost of a new gas furnace fairly soon, and we want it as efficient as possible. We still have to make decisions and the problems I have delineated above are confusing us.

[tipsrfine]

You say your heat load calc you performed 10 years ago came up with ?127,000, but then you've had quite a bit of weatherization performed? That weatherization should have reduced your heat load, so maybe you should do another one to see what size you need now.

[motoguy128]

I thought it's called "Queen Anne". All the normal Victorian traits (assymetrical, ornate woodwork including "Gingerbread" on the outside trim. Usually dark wood work. Basically, the house says "look at me", bright contrasting color schemes) but Queen Anne have turrits of varying styles.

FWIM, 3800sqft isn't that big for that period. We have a bunch that are 4000-5000sqft in my town with one really, really awesome queen anne that a 600sqft, 6 bedrooms. It looks like a castle!

120k doesn't sound that far off for that size space.

Did you consider splitting it into two systems, one for upstairs bedrooms and one for the main floor and basement? That's how mine is set up on my old home and I love it. Upstairs usually need less, so you could go 45 of 60k upstairs and 60 or 80k downstairs.

For hot water, personally I have the same issue and ended up going with a Navien "A" model tankless and installed some recirculation return loops to give me nearly instant hot water at most of my sinks and shower. But you need to have copper or PEX piping. Never recirulate with galavanized or iron water pipes. THe unit has been troublefree for 3 months and at 300k BTU, I don't think I can even supply it enough water hardly to reach max capacity. No real change in my bills overall. The recirculation loop probably balanced out any savings I got from the effciency and standby losses. But I'm saving water overall. I see some savings in winter when the recirculation losses are "free heat" in the home and water temps are lower so unit effciency is higher and we take longer hotter showers.

Along those same lines, you might also consider a conventional furnace for the downstairs and get a combi boiler for hot water and for a upstairs air handler or even multiple air handlers depending on your floor plan. That wuld give you the best comfort and leave you with only 2 appliances.

[2old2rock]

2 systems is the best in your situation.
You'll need to find a very good contractor that can explain all the options clearly.

[beenthere]

I'd redo that load calc, or at least look at it again, and make sure nothing was missed.

You could have the first and second floor duct work separated and get 2 smaller furnaces. That would allow you to get VS blowers on one or both of them. Would also eliminate your reason for wanting a VS blower.

[abcs]

[QUOTE=motoguy128;13985791]I thought it's called "Queen Anne". All the normal Victorian traits (assymetrical, ornate woodwork including "Gingerbread" on the outside trim. Usually dark wood work. Basically, the house says "look at me", bright contrasting color schemes) but Queen Anne have turrits of varying styles.


The real high Victorian style is Queen Anne. Some people use "Princess Anne" to refer to a later, Edwardian transitional house like mine, which has many of the features of a Victorian but also a bit of Colonial Revival. We do have a 3-story turret and lots of odd-shaped rooms.

Splitting into two systems would be very complicated without redoing the ductwork. So, does 120,000 in a 95% efficient furnace not seem too undersized? Is a two-stage, variable speed system better enough to be worth going for the smaller size, or are we better off with the single-stage, larger furnace?

I could redo the heat load calc. I am kind of astonished that not one contractor wanted to do one, and only one even went around the whole house eyeballing every room. They're all basing their estimates on the size of the present furnace and what I tell them is the square footage of the house.

[BaldLoonie]

The Allied brands have a 2 stage variable speed blower 95% with output right at your heat loss. Since it is based on a Lennox furnace, they may as well.

[motoguy128]

DO you have any supplemental heat sources you use like a direct vent fireplace? You could plan on using that in the coldest weather, and a 120k BTU would work just fine.

Depending on the ductwork layout and access you can install a zone system. On a zone system, you can often use a slightly undersized furnace since both spaces usually won't need maximum capacity at the same time. Some zones system are also modulating os you can zone individual rooms.