Heat Pump in 100 yr old home in DC?

[stephen298]

Hi – I am investigating the installation of a new HVAC system and ductwork in my home. The house is approx. 2700 sq. ft, 100 years old, and solid brick, with 10ft. ceilings, 4 levels (including basement), and is located in Washington, DC. The house also has original, “doghouse” style skylights above an open, 3 level “atrium” that the main staircase winds around, and in the 3rd floor bathroom as well. There is no insulation in the house, and the previous owners installed what appear to be builder-grade vinyl windows.

HVAC-Calc (with the predefined parameters for DC) says that the heat loss for the top 3 floors (1900 sq ft – the 800 sq. ft. basement will be conditioned separately) is approx. 126,000 BTU/h. Blowing insulation in the attic (I believe R-19, or 4-6.5 in, can be achieved) and installing new double-pane, low emittance windows brings the heat loss down to approx. 96,000 BTU/h. Is installing a heat pump feasible for this type of application? I had been looking at a duel fuel system - would an A/C unit paired with a high efficiency furnace provide better comfort and/or energy efficiency?

Next, should I ask the contractor to perform his own Manual J calculation, or will this calculation suffice (the square footage was taken from architectural drawings)?

Finally, in researching heating and cooling options, I have learned that houses such as mine were meant to “breathe”, while newer construction is built to be “tighter”. For example, the skylights have metal vents that can be opened and closed. Should the original skylights be replaced newer, sealed skylights? The house also has 3 fireplaces that are currently sealed. Is it realistic to expect to achieve the “best” category of air leakage (combustion air from outdoors, glass doors, dampers) when the fireplaces are opened?

Thanks in advance for your help. This site has been an invaluable resource!

Stephen

[dan sw fl]

Hi – I am investigating the installation of a new HVAC system and ductwork in my home. The house is approx. 2700 sq. ft, 100 years old, and solid brick, with 10ft. ceilings, 4 levels (including basement), and is located in Washington, DC. The house also has original, “doghouse” style skylights above an open, 3 level “atrium” that the main staircase winds around, and in the 3rd floor bathroom as well.

There is no insulation in the house, and the previous owners installed what appear to be builder-grade vinyl windows.

Blowing insulation in the attic (I believe R-19, or 4-6.5 in, can be achieved) and installing new double-pane, low emittance windows brings the heat loss down to approx. 96,000 BTU/h.

1. Is installing a heat pump feasible for this type of application? I had been looking at a duel fuel system - would an A/C unit paired with a high efficiency furnace provide better comfort and/or energy efficiency?

2. Next, should I ask the contractor to perform his own Manual J calculation, or will this calculation suffice (the square footage was taken from architectural drawings)?

3. Finally, in researching heating and cooling options, I have learned that houses such as mine were meant to “breathe”, while newer construction is built to be “tighter”.

Thanks in advance for your help. This site has been an invaluable resource!

Stephen

Stephen,

100 year old, 3 story Washignton DC residence is a
Very Complex HVAC application.

1. Yes, dual fuel would work with a higher than normal balance point.

2. Yes, you need a fully developed HVAC design, but I would not attempt this calculation myself ( even after already performing > 400 Manual J calcs for various regions of the U.S.) without a blower door test on an upgraded thermal envelope.

3. I understand that "Breathe" in this situation means out-of-control infiltration.
What will the wall upgrade involve?
Foam insulation?

[beenthere]

Those sky light vents were to help keep the place cool in summer, not needed on homes with A/C.

Any and all improvements you make now, keeps your heating and cooling cost down every year afterwards.

You should be able to find a good contractor somewhat close to you that has the experience to do your home. May not be from DC, but close.

Dual fuel would be ok for your home.
But as Dan points out, tends to have a higher balance point then newer homes.(70 years old)

[tigerdunes]

Stephen

I suggest that you have one of your quoting dealers to provide a Man J heat/cool load calculation in writing for you to compare against your results.
Those heating BTUs seem questionable considering the improvements you plan to make. What were your cooling BTUs?

I recommend a Carrier Infinity Hybrid system or Bryant Evolution Hybrid system. ANd have dealer make a complete inspection of your ductwork system for type, size, condition, supplies/returns, insulation properties,etc.
Dealer may be able to offer suggestions on tightening up your home.

IMO

[beenthere]

Be prepered to pay for it.
Thats not something that is provided for free by most. Since we don't do them for the competition to use against use.

[stephen298]

Stephen,

100 year old, 3 story Washignton DC residence is a
Very Complex HVAC application.

1. Yes, dual fuel would work with a higher than normal balance point.

2. Yes, you need a fully developed HVAC design, but I would not attempt this calculation myself ( even after already performing > 400 Manual J calcs for various regions of the U.S.) without a blower door test on an upgraded thermal envelope.

3. I understand that "Breathe" in this situation means out-of-control infiltration.
What will the wall upgrade involve?
Foam insulation?

Thanks Dan. My responses below:

1. I suppose I could calculate the heat loss over a range of outdoor temps to see what the balance point would be, then determine the payback period for the incremental cost of the heat pump combined with running it for a shorter period of time?

2. Thanks. It sounds like installing new windows and blowing in the attic insulation first (in addition to doing the blower test) would be recommended, rather than relying on the reduction in heat loss projected by HVAC Calc (or a Manual J)?

3. My home appears to be constructed in the manner described here:

http://www.askthebuilder.com/610_How...ick_Home.shtml

I don't think insulating the walls is an option for me, unless I were to frame new walls in front of them and fill with insulation.

[beenthere]

Unless your OD temps drop below -30F, your heatloss is linear.
Atleast at night time when there is no solar gain.

So 0 BTU loss at 65°F, and your 96,000 BTU after insulation at your OD design temp is all you need for the homes heatloss. But you need the BTU outputs of the heat pump. To graph your balance thermal balance point.

[stephen298]

Stephen

I suggest that you have one of your quoting dealers to provide a Man J heat/cool load calculation in writing for you to compare against your results.
Those heating BTUs seem questionable considering the improvements you plan to make. What were your cooling BTUs?

I recommend a Carrier Infinity Hybrid system or Bryant Evolution Hybrid system. ANd have dealer make a complete inspection of your ductwork system for type, size, condition, supplies/returns, insulation properties,etc.
Dealer may be able to offer suggestions on tightening up your home.

IMO

Thanks tigerdunes. I will ask the dealer to provide a Manual J as well.

The heat gain was calculated at approx. 50,700 BTU/h based on existing characteristics, and approx. 39,200 BTU/h after new windows and R-19 in the attic.

I am leaning heavily towards the Infinity system. Based on what I've read, I would like to go with a 2-stage recip since its low stage will perform better at humidity control compared to a 2-stage scroll. While it appears that pairing a HE furnace with a heat pump is discouraged, I think I would go with a HE if I end up getting a heat pump given the amount of heat loss in the home.

[dan sw fl]

With TWO 3-ton heat pumps,
the thermal balance point would be about 35'F

[aaCharley]

You don't mention what the heating system is now.

However, the solid brick / block masonary wall is really not too bad. It should combine for a pretty good thermal mass and not allow much infiltration through the walls. If it were me, I would probably not spend the money or go through the trouble to squirt the insulation behind the plaster. It would screw things up pretty good if you every wanted to try to run some wiring. Putting some into the attic is pretty effective and not too much cost.

As to the windows, I would be careful to consider the change in the historical character of the building that will come about from the window change. A great deal of the heat loss can be stopped with simply making sure that there is a good seal around the doors and window frames you have now. Sure, new windows will allow less heat loss. But with some fairly high costs in $$$$ and loss of character. Considering the costs of housing there, is it really important to save the last $150 a year on the energy bill by replacing windows?

Even distribution of the heat and air in a four story home will be a challenge. Heat pump is pretty darned efficient and particularly for the Washington, DC climate. Using gas for the back up will make sure that the home is comfortable in the worst cold weather. Good luck with your project.