[adisb]

I just got a few estimates for my 792sq ft ranch on a crawl space and some say they would install a 70K BTU furnace and a 2 ton AC, others say they would install a 50K BTU and a 1.5 ton AC. One of them said that they will cut 4 10x6 heat supplies in the ductwork in the crawl space to condition (Heat) the space for the winter - a waste in my mind but they argued that it will keep the pipes from freezing.

The house is built in 1954 but I will have all new windows installed so, heat loss through the windows will be minimal.

Based on my readings on-line, a 45k BTU furnace and 1.5 ton AC should be sufficient??? Why oversize to 70K BTU and have the systems cycle on and off a lot?? I am in Michigan.

Any thoughts would be appreciated. Thank you in advance.

 

[dac122]

I agree 70K BTU sounds high, but without a load calc I cannot be sure. Did anyone do a load calc, aka Manual J? That is the only way to be sure.

Why are they considering conditioning that crawl space? Have you had freezing pipes in the past? There are more economical ways to prevent freezing pipes.

 

[Scuba_Dave]

My last house was built in 1905 - crawl space under
The floor was insulated
The outside walls of the crawl space were not insulated or even sealed 100%
I insulated the pipes in the basement
I also ran a heat tape on the main feed pipe for added safety

The furnace was located in the basement as were the insulated heating ducts
I never had a frozen pipe

My house before additions is around 1700 sq ft w/2nd floor
My manual J indicated I needed around 68k BTU heating

Ask to see the manual J calc they did
Do they know you are installing new windows?
Are the old windows single pain

 

[adisb]

I agree 70K BTU sounds high, but without a load calc I cannot be sure. Did anyone do a load calc, aka Manual J? That is the only way to be sure.

Why are they considering conditioning that crawl space? Have you had freezing pipes in the past? There are more economical ways to prevent freezing pipes.

Thanks for your quick response. There were no issues of pipes cracking in the winter (the pipes are not insulated but I plan on buying the foam insulation and insulate the pipes).

Also, none of the contractors have performed a load calc. They all responded that it is a typical ranch/crawl/etc and that they know from experience what system would be adequate.

 

[adisb]

My last house was built in 1905 - crawl space under
The floor was insulated
The outside walls of the crawl space were not insulated or even sealed 100%
I insulated the pipes in the basement
I also ran a heat tape on the main feed pipe for added safety

The furnace was located in the basement as were the insulated heating ducts
I never had a frozen pipe

My house before additions is around 1700 sq ft w/2nd floor
My manual J indicated I needed around 68k BTU heating

Ask to see the manual J calc they did
Do they know you are installing new windows?
Are the old windows single pain

Yes, the old windows are single pane (wood) very poor quality; now I will have double pane Low E argon gas windows which should make a big difference in the heat loss issues.

I will insulate the pipes and that should suffice to prevent the pipes from cracking - they did not crack in the past.

 

[Home Air Direct]

Sorry: I wrote the below before seeing you were in MI.

It is obvious that a load calc needs to be done, but I think a big missing piece of the puzzle is "Where" you live. If you live in Orlando - vs - Detroit, both cooling units could be viable answers. In the same, the furnaces could both be utilized (though the 70k seems a little big for either, unless you have wind blowing through your house).

45K is as small as you can go with most conventional furnaces, so even if the load calc says smaller, that will be your choice.

One of the problems is that one of the contractors may do the load calc and the answer will still be 2 of those 4 pieces of equipment, and the contractor might feel it is a waste of his time when he was right in the first place, but the reality is that you own your money and you have all the power in the decision, and if you want a load calc before deciding, the contractor should respect that or move on.

Good Luck

 

[Yoyizit]

If you get enough bids, you can probably tell what you really need. To get 5 bids you may need to call 10 or 15 contractors.

.........a...bcd...e.........f
$0....1.....2.....3.....4.....5
........^relative price^

Bids a and f are probably outliers, and bcd seems to be the true price of doing your job in your zip code, today.

Incompetence and/or greed may cancel out to some extent with this method.

How many therms do you usually use per winter and cooling kwh in the summer?
1 Therm of energy can be had from approx. 0.71 gal of fuel oil, 100 cubic feet of natural gas, 1.1 gal of propane, 29 kwh of elec heat, 8.4 kwh of heat pump heat (COP = 3.5) and 4.2 kwh of heat pump heat (COP = 6.9)

My oversized furnace is only on 1/4th of the time in a cold winter.
At 4800 BTU per Heating Degree Day for your house size, this link along with your nearest city
http://www.degreedays.net/
will give you a rough idea of how many BTUs you need.

 

[adisb]

If you get enough bids, you can probably tell what you really need. To get 5 bids you may need to call 10 or 15 contractors.

.........a...bcd...e.........f
$0....1.....2.....3.....4.....5
........^relative price^

Bids a and f are probably outliers, and bcd seems to be the true price of doing your job in your zip code, today.

Incompetence and/or greed may cancel out to some extent with this method.

How many therms do you usually use per winter and cooling kwh in the summer?
1 Therm of energy can be had from approx. 0.71 gal of fuel oil, 100 cubic feet of natural gas, 1.1 gal of propane, 29 kwh of elec heat, 8.4 kwh of heat pump heat (COP = 3.5) and 4.2 kwh of heat pump heat (COP = 6.9)

My oversized furnace is only on 1/4th of the time in a cold winter.
At 4800 BTU per Heating Degree Day for your house size, this link along with your nearest city
http://www.degreedays.net/
will give you a rough idea of how many BTUs you need.

thanks for your input ! to answer your question - I have no knowledge about prior usage since I have bought the house just after the winter season ended (Michigan). I have narrowed it down to 80% 45/50K BTU (still have to verify that this is the correct size; but for 792 sqft I cannot believe I need 70K BTU) and a a 1.5 Ton AC unit.

There are 4 contractors within the same price range installing the following and I an having a hard time deciding which one to pick based on the brand:

1. Carrier
2. Payne
3. Rheem
4. Comfortmaker

Any recommendations on which one would be a better unit?

 

[Yoyizit]

There are 4 contractors within the same price range

If the prices don't visibly clump together
you might get one or two more bids or
try to decide based on the references of the contractors, or
warranty length, or
the prices of critical parts, like the controller board (which you can find by calling HVAC supply houses). These boards tend to be delicate and expensive.

Michigan is not particularly prone to lightning strikes (see Fig. 8.1 in the link below)
http://books.google.com/books?id=SY...ahqMEB&sa=X&oi=book_result&ct=result&resnum=3
but you may want to invest in surge protection, perhaps just for your HVAC stuff.

"All major HVAC manufacturer's make systems under different brand names. Ruud is manufactured by Rheem and is considered to be of above average reliability. Trane is manufactured by American Standard (the parent company) and is considered to be higher reliability.

Looking at a report on HVAC reliability published by a leading consumer reporting organization, here were the top rankings:

1. American Standard
2. Rheem
3. Trane
4. Ruud
5. Bryant
6. Carrier"