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Old 02-03-2018, 05:12 PM   #16
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Re: New construction and furnace question


Exterior will be some form of rigid insulation. when I re sided my current home with it, I believe we used 1/2" formular it made a massive difference. As far as 2 units goes, it is the norm around here. Every home built is doing it, I ran through my paperwork furnaces will be 90 afue I can always pay a little more for 95+. Lots of good information on here so far. I have a ton of reading to do. This is a HUGE thing to me and it has be done correctly. Finishing I can always do later, I can't re insulate or change my hvac after the fact. If I go the foam route it will cost me a kitchen island. As said I can just add it a year or 2 down the line.
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Old 02-03-2018, 05:48 PM   #17
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Re: New construction and furnace question


with exterior foam, if you put like 1.5 - 2", doing spray foam as well will be overkill.

just make sure they don't oversize doing two systems. you'll be surprised at how low the heat loss will be with good insulation, probably 70 000 btu/hr or less for whole house. unless u have high ceilings.

don't let them put two 60 or 80k btu input furnaces.
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I am not in the business of any trade I give advice on. I have non-professional hvac experience + good knowledge of theory. Attempt repairs at your own risk. Never jump out safeties - especially pressure switches - on a furnace for testing with fuel supply on; use a meter. Do not troubleshoot with live line voltage present unless there's no alternative.
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Old 02-03-2018, 06:41 PM   #18
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Re: New construction and furnace question


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Originally Posted by user_12345a View Post
An extra 5 to 10 grand at least plus double the repair and maintenance costs? vs maybe putting a gas fireplace somewhere for some emergency heat?
It shouldn't be anywhere near that when it's part of the planning stages. I'd expect just slightly above cost for the second unit. Don't forget that changing from the standard layout of tract housing will actually cost more even when it's less material. I dunno if this is applicable to the OP though. Even for a custom house, the ductwork is nearly the same for 1 or 2 systems. Very little extra material. (PS. I'm currently working on one with multiple sir handlers.)

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Originally Posted by user_12345a View Post
with exterior foam, if you put like 1.5 - 2", doing spray foam as well will be overkill.

just make sure they don't oversize doing two systems. you'll be surprised at how low the heat loss will be with good insulation, probably 70 000 btu/hr or less for whole house. unless u have high ceilings.

don't let them put two 60 or 80k btu input furnaces.
Extra insulation is always better. The question is, can you afford it. Even with diminishing returns, utility bills will only be going up from the present. They can spray in 2 passes. Second layer is done after the plumbing and electrical is done. (Some changes are required to accommodate the spray due to codes.)

(I've seen 4" on the walls, 8" on the ceiling, and 1.5" foam cladding on the same house. It all comes down to affordability.)

Cheers!
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Old 02-03-2018, 08:19 PM   #19
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Re: New construction and furnace question


insulation, it's something you pay for whether you buy it or you don't. It's like led light bulbs where even at $10 a pop it's cheaper to use them long term than not.

If there'll be a mortgage, the energy savings could cover the difference in payments - in that case, might as well get the insulation, when mortgage is payed off the insulation continues to save.

The same can't be said for fancy kitchens and bathrooms. People will put extra money into cosmetic stuff without thinking about it, but insulation is too expensive for some reason.

Putting a 1.5 to 2" layer on the exterior of the house, I imagine won't cost more than an extra 4 to 6 grand, the materials probably being half or less of the cost.

Exterior insulation is not like just using thicker batts; the greatest value is greatly reduced thermal bridging - the returns are significant.

Foam would cost more and if doing only 3 to 4" inches, not filling the whole cavity won't produce much of an improvement over standard batts.
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I am not in the business of any trade I give advice on. I have non-professional hvac experience + good knowledge of theory. Attempt repairs at your own risk. Never jump out safeties - especially pressure switches - on a furnace for testing with fuel supply on; use a meter. Do not troubleshoot with live line voltage present unless there's no alternative.

Last edited by user_12345a; 02-03-2018 at 08:23 PM.
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Old 02-04-2018, 07:37 AM   #20
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If possible I would try to avoid two systems. Sure it gives backup protection but with much more cost and chance for failures and increased maintenance. I would also go with the 95% efficiency which will allow for PVC chimney. If there is any way to keep ductwork inside heated space that would really help. Have you considered a dual fuel heat pump? Both air conditioning and heat with the built in gas furnace kicking in when the heat pump cant provide the heat required alone. I designed my new house system with exposed spiral duct
For its heat pump. Just got my Jan electric bill of $99 for heat, lights, hot water, cook stove, electric clothes dryer. House is in TN.
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Old 02-04-2018, 11:52 AM   #21
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Re: New construction and furnace question


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If possible I would try to avoid two systems. Sure it gives backup protection but with much more cost and chance for failures and increased maintenance. I would also go with the 95% efficiency which will allow for PVC chimney. If there is any way to keep ductwork inside heated space that would really help. Have you considered a dual fuel heat pump? Both air conditioning and heat with the built in gas furnace kicking in when the heat pump cant provide the heat required alone. I designed my new house system with exposed spiral duct
For its heat pump. Just got my Jan electric bill of $99 for heat, lights, hot water, cook stove, electric clothes dryer. House is in TN.
No chance im using heat pump or electric. rates are here 19.5 cents kw/hway way way way cheaper to heat with natural gas. I know 3 people with a heat pump all of them hate it. it blows cold air out for way to long before it gets warm.
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Old 02-04-2018, 12:00 PM   #22
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Re: New construction and furnace question


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No chance im using heat pump or electric. rates are here 19.5 cents kw/hway way way way cheaper to heat with natural gas. I know 3 people with a heat pump all of them hate it. it blows cold air out for way to long before it gets warm.
That’s a design issue. You should never “feel” the air. Heat pumps suffer a poor reputation for really no good reason.
More often then not they are poorly designed or used improperly.
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Old 02-04-2018, 01:39 PM   #23
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My rates are only 14 cents. I keep set on 70. I have never seen my 5kw electric back up come on. I do have over the top insulation and inside the heated space exposed commercial spiral ducts. Like the previous poster heat pumps have a undeserved bad rap.
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Old 02-04-2018, 02:58 PM   #24
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Re: New construction and furnace question


In new york area with natural gas available, dual fuel is probably not worth doing. if the furnace was going to be propane or oil it would make sense.

Even at a cop of 3, natural gas furnace would still come out ahead.

The fuel of choice for power plants now is gas so if the cost of gas goes up, so will electricity.

There's no escape from dependence on gas or oil or propane for heating thanks the "green" policies of politicians that have unintended consequences. coal and nuclear are too politically incorrect. we're going to be kicking ourselves when prices spike, there are supply issues, or both.
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Old 02-04-2018, 03:30 PM   #25
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The most politically correct energy policy is China. They installed more solar energy power generation last year than we have done in our entire history. Also installed more wind generation . In the future if we have to stoop so low we can just buy the technology from them. I am for coal as long as they keep the plants 100 miles downwind.
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